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Musings of an Energy Nerd

Martin’s Ten Rules of Roof Design

For the best performance, build a simple roof shape over a vented unconditioned attic

A simple gable roof works in all climates. The house at the top is in Finland; the one at the bottom is in Thailand.
Image Credit: Image #1: Top: Ezioman; bottom: Geoffrey Wheeler
View Gallery 12 images

Lots of things can go wrong with roofs: bad flashing can cause leaks, a poorly designed valley can turn into a slow-moving glacier, and misplaced gutters can do more harm than good. Experienced roofers see a lot of stupid roofs.

Soon after I dropped out of college in 1974, I got my first construction job. I was hired by Edward J. Thornton Roofing Company in Newtonville, Massachusetts. The company paid me $3.50 an hour. For the next 12 months, I installed countless bundles of asphalt shingles and mopped acres of tar-and-gravel roofs with hot asphalt. Every now and then, I also helped Ed, the company’s sheet-metal worker, to install copper valleys and copper-lined cedar gutters on slate roofs.

Most of the time, I was installing asphalt shingles, back in the days before nail guns and portable compressors. We used heavy wooden extension ladders. My staging consisted of 2×12 planks laid on hardwood shingle brackets; each bracket was secured to the roof with three 16d nails. We never had any fall protection.

My tools were simple: a 16-oz. straight-claw Estwing hammer, a Stanley utility knife, a cat’s paw, a chalkline, a measuring tape, a pair of metal snips, and a cotton nail bag. My tool box was so light that I was able to commute to the roofing shop on my bicycle; I strapped my tool box and my lunch box on the rack over the rear wheel. (Fortunately, my boss delivered the ladders, staging, and shingles to the job site.)

I really enjoyed shingling. I still remember the satisfaction I experienced every time I nailed the last few cap shingles on the end of a ridge — especially when the weather was sunny.

Once a roofer, always a roofer. I still shake my head when I drive by a house and see a classic, obvious mistake, like a brick chimney in the middle of a valley. But my eye also catches errors that others miss, like a shingle roof with a badly woven valley between roofs with different slopes. (When the roofer isn’t paying attention, these woven valleys tend to drift to one side.)

I also hate to see asphalt shingle roofs where the slots don’t line up, or a roof without drip-edge at the rakes, or badly planned shingle courses. (A classic error happens when a ridge isn’t parallel to the eave; an inexperienced roofer is surprised by the discrepancy at the end of the job, and the lack of parallelism shows. An experienced roofer snaps lines to gradually correct the problem over 10 or 12 courses.)

I have strong opinions about roofs. Without apology, I hereby present my opinions.

1. Avoid valleys

If you are designing the roof of a new house, try to design a roof without any valleys. Valleys concentrate water and often clog with ice. It’s far more common to have leaks or ice dam problems near valleys than in the middle of a simple sloped roof.

Many valleys exist because of a designer’s conceit rather than necessity. Often, these valleys trace back to the mistaken belief that a chopped-up, complicated, multi-plane roof looks better than a simple gable. It doesn’t.

2. Just say no to dormers and skylights

There’s no reason for a new house to have a dormer. When I see a dormer, I conclude that the designer or the architect made a mistake. They didn’t include enough interior space, and the homeowner was forced to cut a hole in the roof because the ceiling was too low to stand up.

If you want to build a multi-story house, that’s fine. If you want two floors, build two floors. If you want three floors, build three floors. Then build a roof over the top floor. This roof shouldn’t have any deliberate holes in it. The “no holes” rule covers both dormers and skylights.

3. An unconditioned vented attic is better than an insulated roof

It makes more sense to put insulation on the attic floor than to try to insulate a sloped roof, for several reasons:

  • Rafters usually aren’t deep enough to hold a thick layer of insulation; on the other hand, it’s usually easy to add a deep layer of insulation to the attic floor. Insulating the attic floor is also cheaper.
  • If you leave your rafter bays uninsulated, it will be easier to locate roof leaks.
  • It’s easier to air seal the attic floor than a cathedral ceiling.
  • Damp roof sheathing will dry out quicker if it faces an attic than if it is part of a cathedral ceiling.

4. The best roof shape is a simple gable or hipped roof

In a cold climate, the ideal roof is a simple gable. Since gables don’t have any valleys or hips, they are easy to vent. It’s a straight shot from the soffits to the ridge. That’s good.

Chopped-up roofs with a variety of intersecting planes are hard to frame, hard to keep watertight, and hard to vent. Every nook and cranny creates somewhere for pine needles and ice to accumulate. You don’t want any nooks and crannies on your roof.

In a hot climate, a hipped roof makes more sense than a gable, because a hipped roof makes it easier to provide shade on all four sides of the house. In a hot climate, shade is good. Fortunately, people in hot climates rarely have to worry about ice dams — in Florida, it doesn’t really matter if you choose a roof shape that is hard to vent.

In all climates, make overhangs generous. (Roof overhangs help shade south-facing windows in summer, and help keep siding dry on all orientations. Remember: every exterior door needs to be protected by a roof overhang or its own roof.)

If you’re building a gable roof, don’t forget the rake overhangs; most rake overhangs are too stingy. If necessary, frame the rake overhang with full-depth ladder-style outriggers.

5. Don’t reduce the slope of your roof halfway between the ridge and the eave

A good roof plane has a consistent slope from the ridge to the eave. A roof that changes slope at midpoint is disturbing. Especially disturbing is a steep roof that suddenly switches to a shallow pitch (for example, when a porch with a shallow-pitched roof is affixed to a house with a steep roof). Such roofs hold snow and are susceptible to leaks.

6. Asphalt felt makes more sense than synthetic roofing underlayment

Unless you plan to leave your roofing underlayment exposed to the weather for several weeks, there’s no reason to buy synthetic roofing underlayment, a product that costs much more than old-fashioned asphalt felt. I like to use #30 felt, which is heavier than #15 felt.

Besides being more expensive than asphalt felt, most brands of synthetic roof underlayment are vapor-impermeable, so they don’t allow the roof sheathing to dry to the exterior. According to the manufacturers of synthetic roofing underlayment, these products should never be used on unvented roof assemblies.

7. Plumbing vent pipes should penetrate the roof near the ridge

Like chimneys, plumbing vents should penetrate a roof near the ridge rather than near the eave, for two reasons:

  • While ridges are dry, eaves are wet. Eaves see much more water over the course of a year than ridges, so any defect near an eave will leak more water than a defect near a ridge.
  • If you live up north, snow and ice can tear your plumbing vent right off your roof, especially if it is located near your eave. It’s much safer higher up the roof.

In a house with a vented unconditioned attic, it’s easy to install a couple of 45° ells in the vent pipe so that the pipe penetrates the roof near the ridge. The same approach is also possible in a house with a cathedral ceiling, although the rafter bay in which the vent pipe is run will not be as well insulated as the other rafter bays.

8. Choose metal roofing or asphalt shingles

I’m just expressing my opinion here. Clay tiles and slate are expensive. Concrete tiles are fragile and tricky to walk on.

Cedar shingles are beautiful, but they are time-consuming to install and (because of their flammability) are illegal in some jurisdictions. Imitation slate and imitation wood shingles look like they belong on a Howard Johnson’s restaurant.

EPDM and roll roofing, if visible, are ugly.

My favorite type of roofing is ordinary through-fastened steel roofing. It’s available in a wide variety of colors and can be ordered cut to any length. It goes on fast, lasts a very long time, and is recyclable. It costs less than standing-seam metal roofing.

My second favorite type of roofing is good old-fashioned asphalt shingles. They have their downsides, of course — they are made from petroleum, are susceptible to algae, and don’t last very long. But they are affordable, easy to install, integrate well with all types of flashing, and adapt easily to new penetrations or changes to the roof. Asphalt shingle roofing is easier to repair than other types of roofing.

In most areas of the country, it makes sense to order algae-resistant shingles. Otherwise, install a galvanized steel or copper ridge cap; leachate from the ridge cap will keep your shingles algae-free.

9. Get flashing details right

Step flashing should be generously sized; the vertical leg should be at least 6 inches high, although 8 inches is better. Remember, you aren’t going to be bringing your siding down to the roof, so at least 3 inches of step flashing will remain visible under your siding. Each piece of flashing should be bent from a piece of sheet metal measuring at least 8 inches by 12 inches; crease the flashing so that it has two 6-inch-wide legs.

Each piece of step flashing only gets one nail into the roof. Never nail step flashing to the wall — that only complicates the job of replacing the step flashing in the future. If your step flashing begins at the eave, don’t forget to install kick-out flashing at the eave.

When I install step flashing on an asphalt shingle roof, I like to install a sideways course of cedar shingles under the step flashing, installed at 90° to the usual shingle orientation, with the butt end of each cedar shingle facing the sidewall and the tapered edge blending into the field of the roof. (The cedar shingles are later hidden by the asphalt shingle roofing.) These imperceptible shims direct water away from the vulnerable sidewall flashing, and lighten the load of water that the kickout flashing has to deal with.

Chimneys always get two types of flashing to allow the roof to settle without breaking the flashing. I was taught to flash chimneys with 16-ounce copper flashing and lead counterflashing. These days, however, many roofers are avoiding lead because of its toxicity; it’s possible to counterflash chimneys with copper instead of lead, but the copper isn’t as flexible.

Unless the chimney bisects a ridge, every chimney needs a cricket. Make the cricket oversized, so that the two cricket valleys terminate away from the chimney.

Installers of steel roofing often do a sloppy job with flashing. When I install steel roofing, I always plan carefully for any roof penetrations like vent pipes, chimneys, or skylights. Ideally, you want to lap the steel panels at the penetration. One sheet of metal roofing runs from the eave to a few inches above the penetration; then the penetration is flashed. Then a second sheet of metal roofing is installed from the ridge down to a few inches below the penetration, so that the steel roofing laps at the penetration.

10. Anticipate ice dams

If you’re building in a climate that gets snowy winters, your roof should include details to minimize the likelihood of ice dams:

  • Frame your roof with raised-heel trusses.
  • Make sure your ceiling is as airtight as possible.
  • Install a very deep layer of insulation on your attic floor. The insulation needs to cover the top plates of the home’s exterior walls.
  • Make sure there is adequate blocking between your trusses to keep the insulation from spilling into the soffit and to prevent wind-washing.
  • Install ventilation baffles to maintain a ventilation channel from your soffit to the attic.
  • Install two or more courses of self-adhering rubber roof membrane, so that the membrane extends from the eave to a point at least 3 feet higher than the plane of your exterior wall.
  • If possible, make sure your roof has no valleys.
  • If possible, don’t install gutters; if gutters are necessary, make sure that they are installed below the plane of the roofing so they won’t prevent ice from sliding off the roof.

A preemptive comment directed at indignant designers

At this point, many readers are itching to comment on my arbitrary rules. Before firing off an e-mail or posting a comment in all caps, however, you should hear me out.

  • Yes, I know that it isn’t that hard to install roofing and flashing details that keep valleys and dormers leak-free.
  • Yes, I know that my worries about ice dams and roof glaciers only apply in certain climates.
  • Yes, I know that skylights can provide welcome daylighting to dark interior spaces.
  • Yes, I know that many home buyers think that dormers are charming.
  • Yes, I know one reason that designers include dormers is because zoning height restrictions preclude unconditioned attics.
  • Yes, I know that design imperatives sometimes prevent chimneys from penetrating the roof at the ridge.

I have provided design rules from the perspective of a roofer. These rules, of course, are not set in stone, but they are useful principles to keep in mind. Break the rules if you must, but break them consciously, and only for good reasons.

If there is any takeaway to this list of rules, it’s this: Designers who gussy up their roofs with flourishes and do-dads are often insecure. Apparently, they think that a few more Christmas ornaments will wow their clients. In contrast, classic Japanese and Shaker designers had the self-confidence and restraint to recognize that there is no shame in choosing simple, elegant shapes. In my opinion, these Zen or Shaker principles should govern roof design.

Last week’s blog: “Books on Insulation and Energy-Efficient Building.”

95 Comments

  1. Doug McEvers | | #1

    All roof and little else
    Martin,

    I really like your list, I see so many homes with a super complicated roof design and wonder why? Simplify the roof and spend the money saved on insulation and comfort features.

  2. Lucas Durand - 7A | | #2

    Ices dams
    Martin,
    I have a through fastener type steel roof on 1x4 strapping, half-lapped 15# felt and 1/2" plywood over an unconditioned attic.

    I have been struggling with whether or not to install "snow guards" around the perimeter of the roof.
    This seems a bit like installing an "ice dam" - incresing the risk of a leak.

    I take your point about locating gutters lower on the facia to avoid having them torn off.

    But what about the possibility of injury from avalanche?
    I wouldn't want to be standing under the eave if 12 inches of snow suddenly broke loose and came careening down.

    Because the steel panels are back-vented I think it helps create avalanche scenarios...
    Also because the steel is back-vented, I think the felt has excellent drying potential so maybe snow guards are low-risk...

    What do you think?

  3. User avater GBA Editor
    Martin Holladay | | #3

    Response to Lucas Durand
    Lucas,
    Snow guards are sometimes the best solution to the issue you raise.

    My own preference: if possible, entry doors should be located on the gable side of the house. Let the snow slide when it wants to.

  4. Andrew Henry | | #4

    I wish I knew then...
    Martin,

    Good post! I have a regrettably complex roof that I backed myself into because of the desire to add to the size of our house while keeping the very small original structure. It would have been far easier and cheaper to tear down (deconstruct) the original structure and build a house that would be easy to maintain, and also more resilient to weather and future energy constraints.

    Looks cool though, if you don't know any better! Unfortunately I do know better, but most people don't. We all want our fairy tale castles.

    Andrew

  5. User avater GBA Editor
    Martin Holladay | | #5

    Response to Keith
    Keith,
    You're right, of course. I've always been in favor of 12/12 roofs -- they look best, and you can use your speed square to cut the rafters angles -- all cuts are 45°. The ridge is a 90° angle, and the rake trim angles are easy too.

  6. Keith Gustafson | | #6

    re
    I've got one, how about a minimum 4 pitch roof. Mine is 3/12 and 2/12 and leaked like a sieve. I ended up with asphalt and EPDM respectively, all the interesting/green/cool alternatives would not warranty down that low, for good reason. With a lot of neurotic attention to detail, it is watertight, but steeper roofs shed water better. My neighbor has an A frame that is losing quite a few shingles, and does not leak[except for where they made a shallow pitch addition on the back]

    RE: glaciers
    My first winter with the rubber, giant 4 foot glaciers would slowly slide off the roof and fall with huge impact on the deck. I bonded strips of walking pad to the bottom edge and it works perfectly, no slides. The textured surface allows water to pass easily, it actually melts the dam from the bottom. May not be relevant on a steeper pitch, but it does prevent holes in the roof from mounting snow guards

  7. John Brooks | | #7

    12/12 looks best?
    Now that sounds arbitrary to me.....
    Is 12/12 really optimum for shedding snow?
    I am just asking cause we don't get that much snow in Texas
    If 8/12 or 9/12 will do thejob...why waste all that extra material and make the house that much taller.
    The speed square can be used for pitches other than 12
    does it really save that much time to cut rafters at 45 degrees?

    around here there is a markup on roofing when the pitch goes above 8/12
    12/12 is not-so-safe for the roofers

  8. User avater GBA Editor
    Martin Holladay | | #8

    Just an opinion, John
    John,
    As I stated in my blog, "I have strong opinions about roofs. Without apology, I hereby present my opinions."

    In Vermont, 12/12 roofs are traditional. They shed water well, even when using primitive roofing like hand-made wooden shingles. I have seen light through old wooden shingles (standing in the attic) in a house with a 12/12 roof, and the roof didn't leak when it rained.

    Steep roofs are forgiving; shallow pitched roofs are not.

  9. John Brooks | | #9

    but your not building with handmade shingles
    what is the optimum roof pitch in Vermont for shedding snow with a metal roof?
    how about asphalt?
    do shingle installers really prefer to work on a 12/12 pitch roof???

  10. User avater GBA Editor
    Martin Holladay | | #10

    Response to John
    John,
    I'm a roofer. Steep roofs shed water better than shallow-pitched roofs, even when the roofing is wearing out and the flashing has a few minor defects. I like the way steep roofs look, so that's the way I design and build the houses I have designed and built.

    If you don't like the looks of a 12/12 roof, and you don't like to work on a steep roof, you are free to build a roof with any pitch you want.

    I don't know what you mean by "the optimum roof pitch in Vermont for shedding snow with a metal roof." My roof has a 12/12 pitch and metal roofing, and it holds snow all winter, until sometime in late March. I guess if you wanted the snow to slide off faster than 5 or 6 months, you would have to make it steeper.

  11. Lucas Durand - 7A | | #11

    Holding snow on the roof...

    My roof has a 12/12 pitch and metal roofing, and it holds snow all winter, until sometime in late March.

    Martin,
    Is there strapping (ventilation) under your metal?
    What kind of fastening schedule did you follow?

  12. Lucas Durand - 7A | | #12

    Response to John
    John,
    I think 6/12 is about maximum before the rules change a bit.
    At 6/12 my hammer will just stay put on plywood.

  13. User avater GBA Editor
    Martin Holladay | | #13

    Response to Lucas
    Lucas,
    The metal panels are screwed to 1x3s, 24 inches on center, installed parallel to the ridge. So there is air between the roofing and the asphalt felt.

    My memory is that each 36-inch wide panel has four screws into each 1x3 -- but I can't verify that because my roof holds snow. I'd have to get up there with a broom, and I don't feel like that right now.

  14. Jim Hassi | | #14

    Reducing Algae & Moss - Not allowed!
    Martin -

    You wrote:
    "Otherwise, install a galvanized steel or copper ridge cap; leachate from the ridge cap will keep your shingles algae-free."

    While I live in mossy roof country and disagree with the policy because of the life cycle of the asphalt roof (water quality vs. useful life of the product) I am compelled to point out that the practice of using copper or galvanized strips to reduce moss are not allowed in most of Washington's Lakesideca programs, including our local HBA's Built Green program. This is due to the metal's leachates entering the storm water/surface water.

  15. Aaron Vander Meulen | | #15

    Great list, can't argue with
    Great list, can't argue with any of it. If one were to make a list of rules for building, the KISS principle should be #1. I wish I had a picture of the house I just looked at for a friends daughter. Pitched roof hacked onto a sloped flat roof, OSB soffit (guess how that looks) and the kickers, no drip edge or gable overhang. Rule #11, If you don't know what you're doing, don't!

    One question, I understand the pitch change as you described it, feel different about a Gambrel roof? I realize it's a form of cathedral ceiling, but it would be better, right?

  16. User avater GBA Editor
    Martin Holladay | | #16

    Response to Aaron
    Aaron,
    I can live with a gambrel, although it's not my favorite. It's certainly better than the type of roof in the photo accompanying Rule #5.

  17. User avater GBA Editor
    Martin Holladay | | #17

    Response to Jim Hassi
    Jim,
    Does this green building program allow builders to install a galvanized steel roof or a copper roof? If so, why not allow the use of a little flashing? in any case, how can they regulate the installation of flashing? It's virtually impossible to build a roof without flashing.

  18. Keith Gustafson | | #18

    re
    exactly

    the amount of copper or zinc that gets offsite is minuscule. Sounds like a theoretical answer to a theoretical problem. What and there is no problem with aluminum?

    perhaps relevant if you were rebuilding a house on the shore of a reservoir, but only perhaps

  19. Jim Hassi | | #19

    Built Green - No Moss control allowed
    Metal roofs are allowed, but copper flashing is not. We did a project a couple of years ago that was an all copper roof, including copper shingles - but it was not a Built Green certified project.

    Our local Built Green checklist line item states: "No zinc galvanized ridge caps, copper flashing, copper wires or copper/zinc impregnated shingles for moss prevention". We have just reviewed the statewide (proposed) consolidated checklist, and a variation is included there as well.

    As I said - I don't necessarily agree because it is a miniscule problem and it is not uncommon for the North side of a shaded roof to need replacing after 15 years because of moss damage. One local roofing supplier flat out told me that spending money on a 40 or 50 year shingle would not be worth it because wind or moss would damage the shingle long before the 30 year mark anyway. So I look at the cost both to the homeowner and our resources to do that when zinc strips could prolong the useable life.

    Our current project should have a long lasting roof - at least on the South side where it is almost entirely covered with PV panels ;p

  20. Jack Woolfe | | #20

    snow sliding off metal roof

    My roof has a 12/12 pitch and metal roofing, and it holds snow all winter, until sometime in late March. I guess if you wanted the snow to slide off faster than 5 or 6 months, you would have to make it steeper.

    Martin,
    I have a 3:12 through-fastened metal roof. Snow slowly slides off it, especially on the south-facing side. How is it that snow stays on your 12:12 metal roof for months at a time?

  21. Lucas Durand - 7A | | #21

    Hmm...
    Jack,
    That is what I was wondering too...
    I've heard that sometimes the heads of the screws can help hold snow up.
    I thought maybe he had used a LOT of screws...

  22. User avater GBA Editor
    Martin Holladay | | #22

    Response to Jack Wolfe
    Jack,
    I'm not sure why my roof stays snow covered. My best guess is that the snow stays on because our weather is so cold. We really don't get any temperatures above freezing during the winter. Occasionally we'll have a thaw for a few hours, but not enough to get the slow to slide.

    My solar thermal collectors are covered with snow, too, until late March, and it's too complicated to try to clear them. (There isn't enough sunlight to make it worth the effort, and I get hot water from a coil in my wood stove, so I don't really need the solar-heated water in winter anyway.) I have a system for removing the snow from my PV array -- I do it with a broom.

  23. User avater GBA Editor
    Martin Holladay | | #23

    Another response to Jim Hassi
    Jim,
    If a green building program wants to avoid ridicule, it needs a minimum of consistency and logic. "Metal roofs are allowed, but copper flashing and galvanized flashing are not?" Whoever wrote those guidelines wasn't thinking too clearly.

  24. David McNeely | | #24

    Question re penetrations
    I am planning >= 3' eaves with the soffit at the plate line:
    Is there any reason a vent stack cannot turn 180 deg. to vent down from the soffit?
    Same question for bathroom fans?
    Same question for range hood vents?
    Same question for fireplace (just kidding...).
    Seems like avoiding all these penetrations would be a good thing for everyone.

  25. User avater GBA Editor
    Martin Holladay | | #25

    Response to David
    David,
    DWV (plumbing) vents have to go through the roof.
    Bath fan venting from the soffit is possible, but it's a bad idea -- moisture gets pulled back into the soffit vents, and these vents create icicles, rust stains, etc. Go through the gable or the roof.
    Range hood vents - NO! Grease and mess .

  26. Ron Smaron | | #26

    Roof Rules
    Martin,
    Waxing to my poetic days in architecture school, I recall a philosophical discussion a group of us had one time on what defines a house. After many brain enhanced opinions, we all boiled it down to the roof as the defining element of the essence of shelter. Nothing else matters if you don't have a roof.
    That aside, I have four things to add to what you said:
    1. Roof ridge vents (and soffit vents) should be used generously. Especially ridge vents, which eliminate the need for other types of roof venting penetrations. And that includes ridge vents flashed in at vertical walls.
    2. Clerestories are a good way to get light into the center of a building while minimizing roof breaks. It also allows for ventilation, and sun control via overhangs. True, it's a dormer, but at least it's a dormer on the ridge, higher up.
    3. Another roof type might be the combination of a gable and hip, as demonstrated by what I call the traditional Japanese farm house. It's basically a gable roof that partway down changes to a hip, leaving small triangles of wall at the end of the higher gables. Nice form, minimal vertical wall meeting a roof.
    4. Because of global warming issues, roofs should be as light in color as possible. Pure white may not be aesthetic, but we need to bow to a higher directive and start replacing all the lost snow surfaces of our poles with a greater reflectance elsewhere, as in our roads, sidewalks and roofs.
    Now I'd like your opinion on the 10 rules for flat roofs, when you absolutely have to have one.
    Ron Smaron

  27. Kevin O'meara | | #27

    roof rules for snow zones
    I live in snow country, my personal record was 8 feet in 3 days! When you live in snow country you absolutely have to consider where all that snow is going to go, especially if you have a metal roof. Several years ago a child was killed when playing about their house and the snow from the metal roof suddenly slide at all once ("roof-alanch") and buried and killed him! Metal roof tend to shed their snow in sudden sloughs. I have seen this take out underlying decks and deck rails. My favorite is when the roof sheds right in front of the garage door and leaves a wall of heavy concrete like snow barricading entombing the cars inside!

  28. Kevin Dickson, MSME | | #28

    New Plumbing Vent Option for Heavy Snow
    Martin,

    If the snow doesn't slide off your roof until March, your attic is obviously overinsulated :)

    But seriously, do you think your ridge vent or vents are really working when they are sealed shut with snow? Or do you have gable vents only?

    I couldn't find a link to the new code, but I'm told that DWV stacks are now allowed to go out the gable. This was helpful for a cabin I built in Montezuma, CO at 10,600'. You can also eliminate most of the exterior plumbing vents by using AAVs (Studor vents).

    Also just an opinion, but I believe cost effective insulated roofs can be accomplished with 12" SIPs. In fact, if you just add a 3' kneewall to the attic, then SIPs gain you a bonus room that is worth far more than the extra cost of the SIPs. Just watch those air sealing details between panels and at the ridge beam.

    Here again, a simple gable is preferred, and ice damns never occur on a 12" SIP. Ever.

    Here's a roof problem with no solution that I'm aware of:
    Gutters are needed in snow country in the summer. Unfortunately, snow will tear them off if the ice doesn't tear them off first. Heat tape is still the only non-solution that I see in CO.

    Another idea tried and failed is to drop a sturdy gutter below the point that sliding snow would touch it. The problem is that the water from heavy summer showers will also overshoot the gutter.

    In Europe, their answer is super heavy duty roofs and gutters with massive tile and 3/12 pitch. The idea is to let the entire winter's worth of snow pile up and melt in the spring. I hate that solution because of cost.

    Has anyone seen a gutter design that works for heavy snow areas?

  29. User avater GBA Editor
    Martin Holladay | | #29

    Response to Kevin Dickson
    Kevin,
    Q. "Do you think your ridge vent or vents are really working when they are sealed shut with snow?"

    A. Snow is not an air barrier, so there is some ventilation that occurs through ridge vents during the winter, although not as much as later, when the snow melts. My plumbing vent pipes are high enough to poke through the snow. As Bill Rose as taught us, however, worrying about attic ventilation is misplaced worry. My usual advice is, if you have a ceiling air barrier and install deep insulation, your ventilation details become less important.

    Concerning roof-alanches: snow guards can limit the problem, and asphalt shingles are always an option.

    Concerning gutters in snow country: It's possible to have a roof without any gutters. That's what I did on my own house.

  30. Kevin Dickson, MSME | | #30

    No gutters are OK, but they are desirable.

    Here's one more thing for your "Yes, I know list":

    "Yes, I know that the insulating value of the snow on the roof (R-1 per inch) is wasted with a ventilated attic."

    It's sort of like having a roof that has free extra insulation during the coldest part of the year.

  31. Garth Sproule 7B | | #31

    Question for Kevin
    You say that ice dams never occur on a 12" sip roof...Seems to me that as snow accumulates on a sip roof that the thermal gradient will keep moving outwards, raising the surface temperature, until such a point that the snow will start to melt at the surface of the sip, causing an ice dam at the eaves. How much snow would it take?? Can someone do the math?

  32. User avater GBA Editor
    Martin Holladay | | #32

    R-value of snow
    Kevin,
    The R-value of snow is often overestimated. The most reliable sources report an R-value of about R-0.5 per inch for fresh, dry snow. As the snow gradually consolidates and becomes denser, its R-value drops.

  33. Jesse Lizer | | #33

    Gutters
    Martin
    You mention not using gutters. My question is how are people getting away with not using them. I would love to not use them, however with a basement, you have water issues if you allow the water to run off the roof. I typically do my best in designs to put a gable over the garage and door ways to eliminate the need for them there (and now falling infront of the doors) but gutter the rest of the house typically.

  34. User avater GBA Editor
    Martin Holladay | | #34

    Response to Jesse
    Jesse,
    In many locations, sloping the grade away from the foundation is enough to keep your basement dry, especially if the foundation has good footing drains that drain downhill to daylight.

    If you need to, you can install "underground gutters" at the dripline of your roofs -- basically trenches lined with EPDM rubber, filled with crushed stone and perforated drainage pipe. Again, slope the pipes downhill to daylight. Cap with landscape fabric and more crushed stone.

  35. Doug McEvers | | #35

    Gutters
    It appears to me some of the "leaf guard" gutters may have some snow and ice shedding ability. They do cover most of the gutter, I will keep an eye out for homes that have them and observe this winter.

  36. Keith Gustafson | | #36

    re
    Large overhangs are good for several things, eliminating gutters is one of them

    I end up with 4 feet from drip line to foundation, and I have found evidence of only one water problem[where it had smaller overhang]

  37. Kevin Dickson, MSME | | #37

    Response to Garth
    Yes, because of the insulation value of snow, it is theoretically possible for ice to occur under the snow on a 12" SIP. But in the real world it's a rare combination of phenomena.

    From the BSC website for Aspen, CO:
    "Ice dam protection – The combination of adequate insulation just above the exterior wall, and air sealing at the wall-roof assemblies transition are essential to prevent ice dams. But ice dams can occur even in properly detailed roof assemblies from differential solar snow melt. A water protection membrane over the entire roof surface is recommended on all roof assemblies in this climate."

    Higher roof slope reduces the thickness of the snow, and the likelihood of buildup
    Martin's recommendation of corrugated roofing does solve the problem, since it's self-vented. The external fasteners do hold the snow a bit. Fasteners hold the primary room for improvement for self-vented metal roofing.

  38. User avater
    James Morgan | | #38

    Lot of good sense in list, but...
    roofs that change pitch as in #5 are traditional and ubiquitous down our way. They work just fine. Boy, am I glad I don't live in snow country. What's an ice dam? ;-)

    12/12 has a certain appeal although it tends to looks more like a 60° or tighter ridge angle from close up, 10/12 is more likely to look like an actual right angle at the ridge. Regional variations are important: FWIW 10/12 is the most common roof slope for older farmhouses in my area, and we have a lot of quite handsome 1920's/1930's bungalows with 9/12 roofs. My roofer buddy tells me his favorite slope is no less than 7/12 and no steeper than 9/12. Easier on the back than a flatter pitch, and safe to walk.

  39. Kevin Dickson, MSME | | #39

    Chimneys not required on a new home
    Talk about your vanity feature - a brick chimney on a new house in 2011? Really?

  40. User avater GBA Editor
    Martin Holladay | | #40

    Response to Kevin Dickson
    Kevin,
    For more on brick chimneys, see Farewell to the Chimney?

  41. Michael Fetterman | | #41

    step flashing
    The last photo shows a kickout flashing and a step flashing. Your comment is that only one thing is wrong...the flashing should only be nailed through the roof and not to the wall. I was taught and have always thought that the opposite was true. I place one nail high in the corner on the downside of the slope to secure the flashing to the wall. I have always felt it is best to avoid a nail through the roof at that location. i also install a membrane flashing up the wall and on the roof surface, if possible. On a re-roof where the siding is left intact I lay a strip of membrane on the roof along the wall. I try not to use any roof cement on the flashing either. I think this traps more water than it keeps out. I would like to hear your thoughts.

  42. User avater GBA Editor
    Martin Holladay | | #42

    Response to Michael Fetterman
    Michael,
    It's true that you will hear conflicting advice when it comes to the question of nailing step flashing. Some roofers advise only nailing the roof; some advise only nailing to the wall sheathing; and some (these are the ones you should certainly ignore) nail both.

    I don't think that nails in the roof are a problem. If the roofing is asphalt shingles, you have plenty of nails in the roof already, and these nail holes don't leak, because the nails are lapped by the next course of shingles. So it's not as if one nail in the step flashing (as long as you nail high enough) is going to cause any problems. If you ever need to readjust or remove that nail, it's a simple matter to lift the nail with a flat bar.

    However, if you nail the step flashing to the wall, removing the step flashing in the future is a major operation that usually involves removing the bottom courses of siding. If you are lucky, however, and the step flashing has no nails into the wall, you may be able to remove the step flashing with a pair of pliers. And you may be able to slip in new flashing without removing the siding -- at most, you may have to loosen the siding nails to create a little wiggle room.

  43. Eric Johnson | | #43

    Mansard Roof insulation
    I have a mansard roof that needs additional insulation. This design does not have any soffit ventilation. (The almost vertical 2nd story mansard walls have no space at the top to carry air into attic.) If I blow additional insulation into attic, it will touch roof deck near eaves. Is this OK? How to best remedy a bad roof design?

  44. User avater GBA Editor
    Martin Holladay | | #44

    Response to Eric Johnson
    Eric,
    Most codes allow for the construction of unvented insulated roof assemblies, and these can work well. If your insulation is touching your roof sheathing, the insulation can't be air-permeable. You either need to use spray foam insulation against the underside of the roof sheathing, or you need to install rigid foam insulation above your roof sheathing. Either method will keep your sheathing warm enough to prevent problems from condensation or moisture accumulation.

    For more information on building unvented insulated roof assemblies, see How to Build an Insulated Cathedral Ceiling. Although the article discusses unvented cathedral ceilings, the same principles apply to other types of unvented roofs.

  45. Donald Mallow | | #45

    roof in Finland
    How are boards run vertically up the roof slope fastened without through nailing...and do those roofs leak with all the through nailing and all the through joints??? Looks nice, but very risky...

  46. User avater GBA Editor
    Martin Holladay | | #46

    Response to Donald Mallow
    Donald,
    First of all, you have a good eye. You're right that the roof on the house in Bomba Village, Nurmes, Finland, appears to have board-and-batten roofing, with the boards installed parallel to the rakes.

    I'm not familiar with this style of traditional Finnish roofing, but here are some observations:

    1. As I said before, the steeper the roof, the more forgiving it is of minor imperfections. Presumably the nail holes don't leak because of the roof's pitch.

    2. I assume that the boards and battens are nailed to purlins installed across the rafters.

    A close-up photo is attached below.

  47. William Stilwell | | #47

    Walking pad
    Re: Post #5

    What is a "walking pad"?

  48. Donald Mallow | | #48

    roof in Finland
    Martin... Apparently roofs like that were also built in Russia...Either the occupants accepted leaks or they had a detail to prevent them...(Certainly there was no Ice and Water Shield)... If they have any drainage plane at all ( felt?) nails have punctured it. It is counter to the roofs we build.... How does one find out about it? Nothing on Google....

  49. User avater GBA Editor
    Martin Holladay | | #49

    Response to William Stilwell
    William,
    I assume that Keith Gustafson was talking about a type of membrane installed on low-slope roofs to provide a durable walking surface for maintenance personnel. One brand is Roof Trak. The illustration below comes from this document:

  50. User avater GBA Editor
    Martin Holladay | | #50

    More on Finnish board roofs
    Donald,
    I found another reference to Finnish board roofs here:

    "The design and construction of the historical building of Pärnu Old Town Basic School started in 1901 and the building was completed in 1902. ... Increase in price of the building didn’t allow building an expensive stone roof, therefore a board roof characteristic to Pärnu was built, which was painted so it would look like a stone roof from a distance. With a correct maintenance the board roof last nearly half a century."

    Here's a web page with links to several photos of Finnish buildings with board roofs:

    Here's a photo posted on Flickr, showing a board roof in Finland. Notice that the boards and battens on this roof are trough-shaped -- a feature that would certainly help make the roof more watertight:

  51. User avater
    James Morgan | | #51

    Roof in Finland
    I think we can assume that traditional roofing techniques in a severe climate such as this will have evolved over time with a combination of materials, roof pitch and assembly details to be both effective and durable in the prevalent conditions of use. Constructional Darwinism - the failures got rooted out generations ago. I've seen similar roofs around here on sheds and outbuildings and I'm sure similar techniques have been used worldwide where there was a good supply of suitable lumber and the climate was not too wet for a wood roof. Couple of thoughts on why this assembly could be expected to work well:

    First, you wouldn't need to through-nail in the way you do for metal: the boards would be nailed near their edges into the purlin and the batten nailed to the board to cover the first set of nails. No single nail would go all the way through the roof system from exterior to interior.

    Further, the nails would be largely self-sealing to the wood in which they were fastened.

    And finally, while I think this assembly would be pretty weathertight as long as it was maintained in good condition, if it began to deteriorate over time I suspect the interior materials of this traditional Finnish home would likely be quite tolerant of a few minor leaks. No sheetrock, no FG batts. Just more boards, and possibly thick lime plaster for a ceiling finish. Old farmhouses hereabouts used through-fastened 5V tin with loose nails and no gaskets for years without serious problems because there was nothing much on the inside to hurt if it got a little damp. Though obviously the format is especially unsuited to the hips, valleys and slope changes that Martin abhors I'd certainly be ready to try this on a simple outbuilding with a non-critical interior. By the way, I'm guessing that the trough-shaped boards in Martin's last post might be a relatively recent adaptation to facilitate a lower slope - this has to be a machine-sawn profile, and perhaps copied from Roman tile?

  52. Keith Gustafson | | #52

    RE William
    Exactly as Martin stated. The ones at the local roofing supply were 30x30" with the double stick EPDM style tape on the back. I cut them in thirds and bonded them at the edge of the roof. the surface is an array of ~1/2" circles ~1/4" high, allowing water to drain by but providing a pretty good 'key' for the glacier. I also added a few in the open field of the roof. Only ones who see it are the deer and coyotes.

    I think it would work on a modest pitch metal roof, and would worst case eventually peel off. I do so hate putting holes in a perfectly good roof...........

  53. Keith Gustafson | | #53

    re leaks
    I think our ancestors were a little more tolerant of a bit of 'weeping ' in their roofs. Their progeny no doubt went to work in the British motor trade designing side curtains and canvas roofs......

  54. Donald Mallow | | #54

    Finish/Russian roofs
    Thanks for all your input...It has been a help....
    I will keep researching....
    I know someone who is contemplating such a roof here, but I have my doubts.

  55. Nicholas Migliaccio IV | | #55

    Reason for the roof framing
    I read your article and definitely liked the points of view that you had brought up. I only disagree partly with a statement you had made. The reason a roof is cut up is because the designer didn't stick to a square box (based on their ego Lol!) but I think that is only a small part of the eqaution. The number of valleys and hips (and any other intersections) is directly based on how many corners a house has. A square box has 4 corners, a typical home today depending on room sizes and foot print has many more. I've framed many homes with cut up roofs and look forward to the challenge... I think the days of square houses went away with the frontier days, and if you have a competent roofer (such as yourself) and not a bunch of migrant workers looking to produce as much work in a day as possible (without thinking of the mechanics and logistics of roofing) thats when you have problems. Anything can be water proofed, if it's made by man it can be solved by man

  56. Steve P | | #56

    Metal roofing and SIPs
    I've got a cottage in Maine that was built post & beam with SIP walls and roof. The roof is a simple 12/12 with gable ends, but to get the height for stairs and an upstairs bathroom we added two shed dormers that start at the ridge (so no changes in slope). The roof itself is SIP panels with standing seam metal roofing. I prevailed on the plumbers to put the vent stack close to the ridge after a friend had the experience of ice and snow decapitating his PVC vent each winter, and I've had no problems. The cottage has a heat recovery ventilator, so there have never been internal moisture issues. It sits on a slab (on footings pinned to ledge) so runoff has never been a problem, but the amount of snow coming off the roof does build up along the sides. There is nothing on the ground there to damage (entry is on the gable end) but there is so much snow that eventually it builds up to the pint that it bounces off and breaks the vinyl siding!

    I've not quite decided what to do about this yet - the holes are small and I have plenty of siding for replacement, but I expect short-term to make up some protective panels to slide in for the winter.

    I suppose one solution for those who need gutters is to use plastic gutters and just unclip them in the fall. It's a job, but not that difficult if the heights are reasonable. If the clips are left in place some may be damaged, but they are cheap and easy to replace in the spring.

    I'd love to have more light upstairs, but the thought of puncturing the roof for a skylight is off-putting. More likely I will add windows to the gable ends - the beauty of P&B and SIPs is the ease of adding windows and doors.

    I once owned a house with a hip roof (Why? Who knows?) where a 6' wide chimney was installed along one wall, resulting in a 6' long ice dam in the winter. It only took me one winter to figure out what a "cricket" was and build and install one. The builder had also neglected a ridge vent. On a hip roof!

  57. User avater GBA Editor
    Martin Holladay | | #57

    Response to Nicholas Migliaccio IV
    Nicholas,
    You wrote, "The reason a roof is cut up is because the designer didn't stick to a square box ... The number of valleys and hips (and any other intersections) is directly based on how many corners a house has. A square box has 4 corners, a typical home today depending on room sizes and foot print has many more. I've framed many homes with cut up roofs and look forward to the challenge... I think the days of square houses went away with the frontier days."

    I also enjoy framing challenges, and you're right -- it can be fun to frame a complicated shape. However, all those bump-outs raise several challenges you didn't mention. In addition to complicating efforts to build a waterproof roof -- the topic of this blog -- bump-outs complicate efforts to build an airtight envelope and drastically lower the home's energy performance. If a designer is trying to meet the Passivhaus standard, these penalties quickly become obvious. Reverting to a rectangle solves many problems at once. If the house is compact, heat loss is significantly lowered, because the area of the envelope is smaller.

    In some cases, a small bump-out (for example, a bay window) can be accommodated without introducing valleys and hips. All the designer has to do is include wide roof overhangs -- wide enough to extend beyond the bay window -- and everything can fit under a roof with a simple shape.

    You wrote, "Anything can be waterproofed. If it's made by man it can be solved by man." That's true. But some roofs are trouble-free for 35 years, while others suffer ice dams almost every winter. The complicated, chopped-up roofs tend to be the ones with chronic problems.

  58. User avater GBA Editor
    Martin Holladay | | #58

    Response to Steve P
    Steve,
    You wrote, "There is nothing on the ground there to damage (entry is on the gable end) but there is so much snow that eventually it builds up to the point that it bounces off and breaks the vinyl siding!"

    It's unclear whether this is a roofing problem or a siding problem. Good luck -- but I can't help thinking that your experience is a good argument for installing fiber-cement siding.

    You also wrote, "I suppose one solution for those who need gutters is to use plastic gutters and just unclip them in the fall." Well, that's an interesting idea, but I doubt whether your suggestion will attract many eager homeowners. I can't imagine adding this chore to my list of twice-yearly tasks.

  59. User avater
    James Morgan | | #59

    Re: square boxes
    Ignoring for now the snarky reference to designers' egos, I'll comment that one of the many practical reasons for moving away from the square or rectangular box is related to the increasing size of the average dwelling. Speaking from long experience, it becomes increasingly difficult to design a home with a simple rectangular shape once the footprint becomes much greater than around 1800 s.f. - if, that is, you place any value on good daylighting and efficient space planning. And of course there are many other potential advantages to an L or other more complex footprint such as the generation of positive outdoor space and the opportunity to work sensitively with compact urban lots.

    Regarding house size, I would be very pleased if I could make a living designing only smaller houses below that 1800 s.f. threshold but the reality is that in the last ten years or so most of my new-home projects have been 2,500 s.f. or above. That said, I have two homes in construction right now both of which have a footprint below 1,000 s.f and they both have clean trouble-free gable roof forms that would make Martin very happy. Maybe there's some good coming out of this recession after all.

  60. User avater GBA Editor
    Martin Holladay | | #60

    Response to James Morgan
    James,
    You're right, of course, that there are many reasons that houses get complex and often have a shape other than a simple rectangle. My own house is now L-shaped, due to an addition, and the roof includes two valleys.

    As I wrote in the original blog, "These rules, of course, are not set in stone, but they are useful principles to keep in mind. Break the rules if you must, but break them consciously, and only for good reasons."

  61. User avater
    James Morgan | | #61

    Eaves, gutters and snow management
    A while back a Danish client requested a roof edge detail which I have seen referred to as a flared eave, in which a 9/12 or higher roof slope breaks to a lower pitch at the wall line, enabling a wide eave to a steep roof without intruding on the window head. I'd previously used this detail on a couple of projects to allow flexible control of solar overhangs - it can be an elegant look though a little fussy in execution, and of course not the only option for that purpose. Framers may complain about it but I've had positive feedback from roofers that it gives them a more comfortable working platform and staging area at the starting edge of a steep pitch. My client told me it was a traditional detail in Denmark, and I wonder if it has some relevance to the roof-avalanche, gutter and ice dam issues mentioned in various posts above, of which I'm happy to say I have no direct experience.

  62. User avater
    Robert Swinburne | | #62

    snow staying on steep metal roof
    I have Noticed here in VT ( Halifax at 1700 feet ) that sometimes a snowstorm will start with a little freezing rain which turns the metal roof into sandpaper which in turn causes subsequent snow to stay put

  63. Jeff Holmes | | #63

    Tile Roof - Our 30+ year experience and druthers
    “Put Your Last Roof on First” That was the roofing material supplier’s slogan. We have lived under a concrete tile roof for over 30 years in western Washington, north of Seattle. There are lots of things I would change about this house (2x4 construction and leaks air like a sieve) but roofing material, that was a good decision. In those days the roofing material of choice was cedar shakes and we have outlasted many of those roofs. The major advantage might be longevity. Very little can damage it. Moss builds up over time but has no effect. Maybe 5 to 10 years, rake it off. The occasional tree limb has given a problem on an out building but easily repaired. Wood cleats and gravity hold the tiles in place so it is just a matter of slipping out the broken tile and replace with the new. We have settled on a 4/12 pitch so easy to access. The building code now might require some nailing which would make repair harder but we weathered 90+ mph winds in 1990 (Artic Express) that toppled 40 or 50 trees getting out our road but moved nary a tile. In fact we used the cedars that fell for board and batt siding for a two-story addition, rough cut with aid of a Volkswagen sawmill and sawyer. The roofing material? Concrete tile.

    Nope, not a salesman for roofing tile but would like to see it more mainstream for all its advantages. And maybe Monier will start making the “Classic” again. Who would have thought that would drop that style, Dang It. Easily installed (valley’s are tough, made that mistake only once), fire proof and lasts for at least a long time. Silent in the rain, not the pinging of metal. And has a natural airflow underneath the tile so it would work well with the non-vented roof. It doesn’t build up heat in the summer or cause ice dams in the winter. If fact our roof is the last place that the snow melts.

    If I could add one more consideration to your list, it would be to stress the roof to carry maximum snow load and then design the roof to hold the snow. The last place I want the snow is stacked up against the side of the house or in the walkways. A European concept that I first noticed in the alpine villages. Comments too long I know. Martin, certainly enjoy your energy musings and other. If you have an email to share would send a picture.

  64. Tony Stephenson | | #64

    General
    Haven't had the opportunity to read every comment yet, so apologies if this is already covered. I'm based in Texas and while we don't get much snow here, foamed attics have been getting progressively more popular over the last 6 or 7 years. I'm regularly repairing roofs and skylights and installing solar attic fans. I have been sceptical of foamed attics for some time on asphalt shingle roofs. I see too many holes in the shingles from wear, hail, hawks/owls and other birds perching on ridgelines for my liking. However, I am starting to get questions from AC contractors that revolve around, "Why do foamed attics smell moist and mouldy?" I am trying to keep an open mind on foamed attics, but it appears apparent that the author too likes well ventilated attics.

  65. User avater GBA Editor
    Martin Holladay | | #65

    Response to Tony Stephenson
    Tony,
    First of all, if an indoor space "smells moist and moldy," that usually means that the indoor relative humidity is too high. In Texas, the solution to that problem is not to introduce more ventilation. Ventilating a space with hot, humid outdoor air only brings more humidity indoors. It doesn't reduce the humidity level.

    If these conditioned attics really do smell moist and moldy, then it's probable that the relative humidity is too high in the whole house. This is common in Houston in well-sealed homes; the main reason is that the cooling load has been reduced to the point that the air conditioner doesn't run for enough hours to adequately dehumidify the house. The best solution to this problem is to install and use a stand-alone dehumidifier.

    Finally, it's possible that the smell actually comes from the spray foam -- especially if the smell reminds you of rotten fish. Here's more information on the lingering odor problem: Spray Foam Jobs With Lingering Odor Problems.

  66. Tony Stephenson | | #66

    Response
    Appreciate the reply. I'll pass the recommendations along and bookmark the website.

  67. Jane Brown | | #67

    Florida roof, Mansard design
    I'm goaling to build a LEED home in northern Florida and am trying to get up to green speed as quickly as possible. Your blogs are very helpful. Curious to know how you'd modify your rules for my climate? And what do you think of Mansard design, dormers and all? Thanks.

  68. User avater GBA Editor
    Martin Holladay | | #68

    Response to Jane Brown
    Jane,
    You probably saw that I advised hot-climate builders to include a hipped roof, because a hipped roof makes it easier to provide shade on all four sides of the house. The inclusion of a porch, especially on the west side of a house, provides further protection from the sun. It's easier for roof overhangs to shade a one-story house than a two-story house, so many hot-climate houses are only one story tall.

    I'm not a fan of dormers, because they reduce the thermal performance of the envelope (like any bump-out) and provide more opportunities for air leaks, thermal bridging, and roof leaks.

    For more hot-climate design ideas, see my article, Hot-Climate Design.

  69. Gavin Farrell | | #69

    Great article
    Enjoyed the read Martin. There definitely is something beautiful about a simple, uninterrupted gable roof.

  70. User avater
    James Morgan | | #70

    Pithy goodness.
    "For the best performance, build a simple roof shape over a vented unconditioned attic."

    I've just realized the echo in my head from Martin's subtitle is the memorable line with which Michael Pollan introduces and pithily summarizes his book 'In Defense of Food':

    "Eat food. Not too much. Mostly plants." In this nuanced world. sometimes, just sometimes, the best advice comes in small packets.

  71. Steve Asher | | #71

    venting closed soffitts in a unvented roof assembly
    Is it required/recommended to vent an enclosed soffit/eave when you have an unvented roof assembly? The eave line is air sealed with rigid foam and caulk. The overhang is four inches thick by three feet wide covered with stucco over densshield soffit board.

  72. User avater GBA Editor
    Martin Holladay | | #72

    Response to Steve Asher
    If your roof assembly or attic is unvented, there is no reason to include soffit vents.

  73. Timothy Smith | | #73

    Note to Indignant Designers
    You wrote: "If there is any takeaway to this list of rules, it's this: Designers who gussy up their roofs with flourishes and do-dads are often insecure. Apparently, they think that a few more Christmas ornaments will wow their clients. In contrast, classic Japanese and Shaker designers had the self-confidence and restraint to recognize that there is no shame in choosing simple, elegant shapes. In my opinion, these Zen or Shaker principles should govern roof design." As a residential designer I couldnt agree more. My problem is clients who INSIST on features such as dormers because it makes the house "cuter" and some realtor has told them it will make the house more "sellable" in the future...ugh! PS: I confess to loving skylights - but only after careful consideration and other alternatives unsuitable...

  74. User avater GBA Editor
    Martin Holladay | | #74

    Response to Timothy Smith
    Timothy,
    I agree that it is hard to find a good solution when a client says, "Please build me an ugly house."

  75. Barbara Tomlinson | | #75

    I think #5 is a very attractive roof shape!
    I approve of all of these opinions, except one. I changed my roof pitch just like in #5. I had a really good reason though. I was using white industrial sheet metal that was leftover from a bigger job so it was only 8' long. My enclosed space is a 12x12 box with 6' added to the back for a bathroom and 6' on the front to cover the front door. I wanted the middle part to have room for a sleeping loft but with a house this small if I had kept up that slope it would have looked very uninviting, like a spear. I disagree that this profile is unattractive. I like it a lot! Especially in a smaller house.

    Of course I don't live where it snows. And I don't know how you make that transition but I did it by turning up the back of the bottom sheet before I put the top sheet on and then I sealed it from below with spray foam. I don't see how water could get in there. I've been through several hurricanes and nothing went wrong. Maybe I have a better technique because I did mine with purlins and not sheathing. If you can't get underneath there I don't know how you'd seal it. I understand in some parts of the world they put plywood under sheet metal but here in Georgia it's acceptable to screw heavy gauge corrugated metal directly to purlins.

    One of my requirements was to build my whole house with no plywood because I'm sensitive to the chemicals in it and I can't lift those sheets by myself. My small sheets of metal were fine. Anything bigger would have been a deal breaker.

    I'll add something about hip roofs in Florida -- you get a discount on your homeowners insurance with a hip roof. They perform better in hurricanes. I love a hip roof but it's hard for a novice to build one. I also don't like the wasted sheet metal because of the angle cuts.

  76. Tim Desmond | | #76

    getting to R-60 on my roof
    Hi Martin, I love this site and just signed up for a pro-account. I'm about to start building my first house. I would love to hear you recommendations for a the most affordable way to get to R-60 in a new roof (I'm on a very tight budget). My design is a basic 4/12 gable using engineered 2x4 trusses. I'm assuming I should blow in a thick bed of cellulose over the bottom chords and cover it somehow to prevent wind washing and vent above it. Is that right? How high should I raise the raise the heel of the trusses at the bearing ends to get a good R value? What do I use to separate the cellulose from the vented space near the bearing ends (where it would want to come right up to the top chords)? Thanks so much!

  77. User avater GBA Editor
    Martin Holladay | | #77

    Response to Tim Desmond
    Tim,
    Q. "I would love to hear you recommendations for a the most affordable way to get to R-60 in a new roof."

    A. Cellulose insulation on the attic floor.

    Q. "I'm assuming I should blow in a thick bed of cellulose over the bottom chords and cover it somehow to prevent wind washing and vent above it. Is that right?"

    A. Most builders don't cover the top of cellulose insulation on an attic floor. However, you need a dam near the soffit to prevent wind-washing in that location (and to keep the insulation from spilling into the soffit).

    Q, "How high should I raise the raise the heel of the trusses at the bearing ends to get a good R-value?"

    A. If you are aiming for R-60, you need 16.5 inches of cellulose insulation. If you want a 2-inch deep ventilation channel above the top of the cellulose, that means that you need at least 18.5 or 19 inches of height at the heel of your truss.

    Q. What do I use to separate the cellulose from the vented space near the bearing ends (where it would want to come right up to the top chords)?"

    A. You can use a commercial product like , or you can install rigid foam or plywood between the rafters. If you use rigid form or plywood, you'll need to first install some 1.5 x 1.5 inch sticks to have something to support the rectangles of foam or plywood.

    If all this is new to you, Tim, my guess is that you are going to have a lot of questions as you build your house. You may want to hire a builder.

  78. Horatiu Vornica | | #78

    Recycled rubber shingles
    Martin,

    What is your opinion about recycled rubber shingles roofing?

  79. User avater GBA Editor
    Martin Holladay | | #79

    Response to Horatiu Vornica
    Horatiu,
    That type of roofing is rarely installed. I have no experience with it, unfortunately.

  80. Rainer Semsch | | #80

    kick out roof flashing
    referring to the last picture in the write-up where you suggest not to nail the flashing to the wall: where do you nail the stucco starter strip?

  81. User avater GBA Editor
    Martin Holladay | | #81

    Response to Rainer Semsch
    Rainer,
    In the case of stucco cladding, I assume that the starter-strip nails will need to penetrate the flashing. There are exceptions to every rule.

  82. Donald F. Mallette | | #82

    One problem I see with an
    One problem I see with an exposed fastener steel roof that has not been mentioned is expansion of the steel when it gets hot. I'm told that a 30' sheet has the potential to grow an inch in hot weather, in which case the fasteners would be compromised. Once those fasteners pull through the wood nailers they must be replaced with oversized screws. That's alright the first time, but what do you use when the oversized screws become compromised?
    Say Martin, how is that coil in your wood stove plumbed into your domestic water system and how do you protect the system from overheating.

  83. Kent James | | #83

    Green roof?
    I certainly understand and appreciate your advice for regular roofs, but on a blog with "Green" in the title, I'm curious as to how you feel about "green" roofs (those that are flat and planted). It seems that they makes sense on many levels (reducing storm water surges, allowing flat roofs to diminish unused building space, reduce heat absorption, reduce carbon monoxide, etc.), but they do present the construction/maintenance issues associated with flat roofs. Are they worth considering, or does your omission suggest that they have no role in residential construction (or even any other construction?)?

  84. User avater GBA Editor
    Martin Holladay | | #84

    Response to Kent James
    Kent,
    Vegetated roofs are expensive to install. Soil is a lousy insulator. Vegetated roofs are a maintenance nightmare. What you want to install on your roof is insulation, followed by roofing. In some cases, you may want to install PV modules. Leave the grass where it belongs -- on the ground.

    For more information on this issue, I recommend by Joe Lstiburek.

  85. Eric Whiting | | #85

    Dormers = traditional design
    I appreciate your article and agree with your primary stance, but with all things in life, opinions are based on perspective.
    Dormers are not mistakes. From a purely energy conscious and ease of construction sense, they certainly are more of a challenge than a straight gable roof. However, the reason architects have included dormers in their home designs for as long as there have been houses are:

    1. Dormers take advantage of living space in the roof area of a house. Sure you can get natural light through the gable ends, but even in shorter runs this can create a tunnel feeling, and a not very inviting or comfortable space for many people.

    2. Dormers create shadow lines and interest.

    3. Dormers lower the scale of a roof to a more human size.

    Most folks will never invest more in any one thing more than the dollars they spend on their homes. And a large part of "home" for many people is a comfortable sense of scale, which can be enhanced in many people's views by cozy spaces tucked into roofs. And while there is no question that a straight roof line with no breaks is clearly the energy and cost winner, quality of life issues such as aesthetic interest, natural day lighting and human scaled design will more often trump energy concerns taken from a check-box approach to design.

    My opinion is that single-window width dormers are useless because of the reasons you mention, but wider, room-width ones are some of the nicest spaces experiencially, and not a mistake, but an intentional design tool for many reasons that cannot be measured.

  86. User avater GBA Editor
    Martin Holladay | | #86

    Response to Eric Whiting
    Eric,
    I wrote, "I have provided design rules from the perspective of a roofer. These rules, of course, are not set in stone, but they are useful principles to keep in mind. Break the rules if you must, but break them consciously, and only for good reasons."

    You are a designer who likes dormers, and you are choosing to break my rules consciously. That's fine; you are the designer.

    As in all matters of design, tastes differ. Personally, I am unconvinced that "creating shadow lines and interest" are much of a benefit.

    Finally, you point out that "Dormers = traditional design ... Architects have included dormers in their home designs for as long as there have been houses."

    It's true that dormers are traditional. But if we look back 200 years, we would have to report that roof leaks are also traditional. Not all traditions are worth preserving.

  87. Eric Whiting | | #87

    Response to Martin
    I saw your disclaimer, but felt the need to respond because I believe in a balanced approach, and that all (good) designs succeed from a balance of structure, aesthetic and function. Sometimes the design calls for simplicity, and sometimes complexity. And with every design decision there are trade-offs.

    As once eloquently stated by another expert on building envelopes...."There are two kinds of roofs. Ones that leak, and ones that are going to leak.".

    Thanks for your input.

    e

  88. Chris Hayward | | #88

    Thanks for nuthin'
    Thanks for your entirely sensible, and fairly depressing list of guidelines. I recognized their clear common-sense with the sinking feeling in my gut that I was going to have to revisit the roof design for the small house I'm building for myself in central Ontario. I'm a carpenter; an attraction to complicated roof lines is something like an acquired occupational illness.

  89. User avater GBA Editor
    Martin Holladay | | #89

    Response to Chris Hayward
    Chris,
    You're welcome.

    I'm sorry to hear that my "entirely sensible" guidelines, characterized by "clear common-sense," were so depressing. Good luck with your project!

  90. François Lévy | | #90

    Cathedralizing the attic makes sense
    I have to take issue with item 3, especially in hot climate zones where HVAC ductwork is frequently located in the attic. It makes much more sense to insulate the envelope and keep R-5 or R-8 ducts within the insulated volume, rather than have them run in a 120° attic. Moreover, it's not too difficult to get adequate insulation in 2x6 rafters with open-cell foam, and 2x8 framing is quite common.

  91. User avater GBA Editor
    Martin Holladay | | #91

    Response to François Lévy
    François,
    As I have written many times, installing ducts in a vented unconditioned attic is a major mistake. If you live in a home where this mistake was made, then you have my sympathy.

    Homeowners who live in homes where this mistake was made should certainly consider transforming their vented unconditioned attic into an unvented conditioned attic, as you suggest. That's what I advised in this 2010 artilce on the topic: Creating a Conditioned Attic.

  92. Roger Smith | | #92

    Bizarre Japanese design
    I saw a TV program last night which featured renovations to a Japanese home. When they showed what they did to the roof, I was surprised. Instead of a normal slope, they reversed it with the sides higher than the center.
    As it is in snow country they showed a wide drain where the roofs meet covered in electric cables and a drain pipe to presumably take away the meltwater.
    That seems to violate just about every one of the tips here for good roof design. The plus-sides are no snow falling off the house to shovel or hit people. I can just imagine ice building up in the gutter, the electric bills, or what happens in a blackout, but apparently it is common.

    For pictures of this, search for murakusetsuyane or 無落雪屋根.
    I'll see if I can find out if this roof system works in practice.

  93. User avater GBA Editor
    Martin Holladay | | #93

    Response to Roger Smith
    Roger,
    It seems that you are describing a type of low-slope roof, often with a parapet, that depends on a center drain. This Japanese variation is sometimes called a "butterfly" roof -- two low-slope shed roofs that drain toward the center of the house, creating a valley. I agree that this is a stupid design. It's particularly bad in snow country.

    .

  94. Clay Whitenack | | #94

    What about solar panels?
    Martin,

    Would your guidelines for no "deliberate" holes in the roof extend to solar panels? For those that have the land, is ground placement by far the best choice?

  95. User avater GBA Editor
    Martin Holladay | | #95

    Response to Clay Whitenack
    Clay,
    Unlike a dormer or a skylight, the racks used to mount PV modules on a roof don't penetrate the thermal envelope. You can have an intact air barrier, insulation layer, and waterproof roofing, and still have solar panels above the roofing. So solar panels don't really create a hole in your roof. (Needless to say, the brackets used to support PV module racks need proper flashing.)

    That said, if you have the option of installing a ground-mounted array or a roof-mounted array, a ground-mounted array is always preferable -- as long as the ground-mounted array gets good solar exposure.

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