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Green Homes

Modern Dream Home is Energy-Positive

TC Legend Homes achieved exceptional energy savings with this modern home tucked into an existing neighborhood in the Montlake area of Seattle.
Image Credit: TC Legend Homes
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The PV system provides enough electricity for the home and an electric car

A Seattle couple spent two years searching for their dream home before deciding to build a new custom home. They turned to zero-energy-home builder Ted Clifton, Jr., who built them a modern two-story house with a mother-in-law suite and views of Lake Washington from the rooftop deck.

Clifton, the owner of of TC Legend Homes, calls the home a “positive energy home” — one that produces more energy than the home itself consumes. In fact, the home should produce enough electricity to power an electric car with the charging station set up in the garage.

The home’s modern asymmetrical design lends itself to the extra-large south-facing roof, which holds 36 photovoltaic (PV) panels rated at 9.7 kilowatts. The home achieved a Home Energy Rating System (HERS) score of -1 with the PV array, or 42 without the PV; a home built to the 2012 International Energy Conservation Code (IECC) would score about a HERS 70.

The home meets all of the high-performance requirements of the U.S. Department of Energy’s Zero Energy Ready Home program. To be certified as a DOE Zero Energy Ready Home, the builder must meet Energy Star Indoor airPLUS and WaterSense requirements, the insulation requirements of the 2012 International Energy Conservation Code, additional DOE Zero Energy Ready Home efficiency requirements, and have renewables or “renewable-ready” measures installed.

This home was part of the 2014 Seattle Green Home tour.

SIPs make for fast construction and a good thermal barrier

Clifton has made a reputation for himself with zero-energy construction in Seattle and Bellingham. (For more information on homes built by Ted Clifton, see A Net-Zero-Energy House for $125 a Square Foot and A Deep Energy Retrofit Using Nailbase Insulation Panels.)

The home features many of the elements that have helped Clifton meet zero energy on other projects, starting with a slab-on-grade foundation with insulated concrete form (ICF) stem walls that provided R-28 of insulation to the sides of the slab. A 4-inch-thick layer of rigid high-density EPS foam under the slab provides an additional R-20 of protection from the ground below. This highly insulated slab helps retain the heat of the radiant floor heating loops installed in the ground floor slab. The concrete slab was stained, sealed, and left exposed as the first floor of the home. The second floor consists of a plywood subfloor over engineered floor joists. The radiant floor loops were stapled up under the subfloor.

The walls and roof of the home were constructed of structural insulated panels (SIPs), which consist of rigid foam sandwiched between two layers of OSB. The foam adheres to the OSB and hardens during the manufacturing process, creating a strong bond and a very sturdy panel. The SIPs are cut to order in the factory, providing straight, clean, and dry walls with high shear strength. The panels arrive at the site ready for quick assembly. The 6-inch-thick walls provide R-26 of insulation; no additional insulation is needed.

SIPs provide an airtight wall because SIP walls have far fewer seams than stud walls. Even so, Clifton’s crew takes additional steps to ensure the airtightness of the building envelope. Where the SIPs connect to the ICF foundation wall, Clifton uses sill seal plus two beads of SIP mastic under the SIP panel. The wall-to-floor seam is caulked all along the inside perimeter of the home, then the baseboard is installed and caulked along the top and bottom edge.

The exterior walls were clad with prefinished smooth fiber cement siding that installs in 4’x8′ panels for a sleek, modern look. Metal Z-flashing was installed between the panels to direct water out at the seams. A corrugated draining housewrap provides an additional layer of protection, serving as a water-resistive barrier under the cladding.

The home has no attics. The roof assembly consists of 12-inch-thick R-46 SIPs that provide roof deck, support, and insulation in one product, making construction of the cathedral ceilings a fast and simple process. The standing-seam metal roofing is highly durable and adds to the modern appearance of the home.

Air-sealing measures address all seams

Before drywalling, Clifton’s crews foam the rough openings and caulk around all the windows; foam behind all the electric boxes and caulk around them; and foam and/or caulk around the electric wires and plumbing pipes. All of the SIP seams are both caulked and taped, in addition to the tape and mudding done by the drywallers. This attention to detail helps Clifton achieve a very airtight building envelope.

The blower-door test result was 0.97 air changes per hour at 50 Pascals pressure difference (ach50), which is more airtight than the stringent 2.5 ach50 specified by the DOE Zero Energy Ready Home program requirements for the marine climate, but not quite as tight as the target specified by the Passivhaus standard (0.6 ach50).

Radiant floor system delivers space heat

Space heat delivery is hydonic, via in-floor PEX tubing installed in the ground floor and second floor. The water for this radiant system is heated by an air-to-water heat pump which operates at a COP of 4.5. This heat pump also preheats domestic hot water, which is further heated in a 50-gallon electric storage water heater. The home benefits from passive solar heating; 80% of the windows face south, allowing any available sunlight to reach the bare concrete slab.

The triple-pane low-e windows have a U-factor of 0.14. The relatively high solar heat gain coefficient (the SHGC is 0.55) lets in any sunlight during the three-quarters of the year when the Northwest is cool and cloudy, while overhangs and deciduous trees that were retained on the lot help provide shading during the summer.

For ventilation in the nearly airtight home, Clifton devised a balanced system that employs relatively inexpensive, quiet and efficient Energy-Star-rated exhaust fans, electronically controlled to work together to bring fresh air into the home and pull stale air out. A 5.4-watt exhaust fan in the laundry room runs continuously at 30 cfm to meet ASHRAE 62.2 requirements. The fan is controlled by a motion sensor that ramps up the fan to 110 cfm during occupancy.

Fresh outdoor air enters the home passively through a duct connected to an intake on the north side of the house. The outside air duct includes a HEPA filter. Each bathroom has its own switch-operated exhaust fan. All ducting for the supply air is in the conditioned space, allowing it to warm up before being delivered. The air is drawn into the home when the bathroom and laundry fans are operating. However, when the higher powered 400-cfm range hood fan is turned on, a 200-cfm inline supply fan connected to the fresh air intake duct turns on to pull in more air to keep house pressures balanced. This powered supply ventilation system may also be timer-operated to come on in the early morning hours during the hot summer periods to remove heat from the home and keep the thermal mass from overheating the inside space.

Energy systems are all programmed and monitored

In addition to the high-efficiency heating and ventilation systems, Clifton also recommended Energy Star appliances and 100% LED lighting for all of the installed fixtures. Low-flow plumbing fixtures reduce water heating demands. Programmable thermostats and an internet-connected monitoring system for the PV array will help the couple track their energy use and production.

These measures, along with the tight, well-insulated building envelope, mean that the 9.7-kW PV system will more than cover the energy needs of the all-electric home. The PV system should produce enough energy to charge an electric car with the car charging station in the garage.

The energy-efficiency upgrades added about $20,000 to the cost of the $700,000 home — a typical price for a home in this desirable Seattle neighborhood. The PV system added another $40,000; however, the homeowners will receive the federal tax credit of 30% of the cost of the system, and because the system was manufactured in Washington state they will also get a production credit of $5,000 per year from Washington state, refunded through the local power company.

The family has had a negative power bill each month since living in the home. “The incremental cost above code has resulted in a highly efficient and energy-saving home. The above-code costs were mitigated by the efficiency of our construction team and the short time frame in which the home was constructed,” said Clifton. “With the federal and state solar incentives and the zero power bills, the upgrades should pay for themselves within five years.”

Homeowner satisfaction may be the biggest sign of success. “Our old house used to have some rooms that were too hot if you turned the heat on all the way, while other rooms were too cold. It is great to have a place where I just don’t even notice the temperature — it is always comfortable. We have a toddler and another one on the way. It is great peace of mind to know that the air quality is good, and we don’t have to worry about her health. Whether you are environmentally conscious or not, having a comfortably heated home, negative energy bills, and great air quality is something that everyone can enjoy,” said the homeowners.

Lessons Learned

Customers need to be convinced that what they see in magazines isn't always great design, says builder Ted Clifton, Jr. In the case of this house, the plans called for shading some of the windows, but the homeowners had a different idea.

“People look at Dwell magazine and see what they want — simple, clean designs — but that doesn’t always work. The original plans drawn by the architect had shading over the windows on the south side. But the homeowners didn't like the look of them so they weren't included. We used high-solar-gain windows, which are good for the winter, but without shading, they allow heat to pass through in the summer. I would prefer to maintain control over those design decisions if I could,” said Clifton.

The project ended up being inspected more often than a conventional home because the city was unfamiliar with some of the processes.

“The city required special inspections every step of the way because we used SIPs. The jurisdiction wasn't as familiar with those construction techniques.”

Clifton has discovered that inspectors, engineers, architects, and yes, builders too, don’t always keep up with the latest innovations from manufacturers. “There is sometimes a disconnect of industrial standards and engineered standards. For example, we learned that we could use thinner nails for much of this project, built with SIPs. Those nails were half the cost of what the plans called for,” he said.

“All of us are responsible to collaborate and on keep up-to-date. We need to provide each other feedback,” he said.

Overall, the building industry hasn’t changed much, he said. “The best place to point a finger is at yourself. Then do it. That’s my mentality. If we want to change it, we all have to step up and pay attention. I learn something new from my entry-level laborer every day. One needs to be open to new ideas and figure out what works best,” said Clifton.

General Specs and Team

Location: Climate Zone 4C, Seattle, WA
Bedrooms: 4
Bathrooms: 3.5
Living Space: 3192
Cost: 200

Builder: Ted Clifton, Jr.,

Construction

Foundation: Slab on grade with R-28 ICFs at slab edge and R-20 horizontal rigid foam under slab

Walls: 6-inch SIPs rated at R-26

Windows: Vinyl windows with low-e triple glazing. U-factor is 0.14; SHGC is 0.55

Roof: 12-inch SIPs rated at R-46; standing-seam metal roofing

Siding: Prefinished fiber-cement siding over wrinkled housewrap

Energy

Heating, cooling and domestic hot water: 5-ton air-to-water heat pump with a COP 4.5 provides hot water for radiant floors and preheats domestic hot water; a 50-gallon electric tank stores water and boosts temperature.

Lighting: 100% LED

Appliances: Energy Star refrigerator, dishwasher, clothes washer

Energy Specs

HERS Index: 42 without PV, -1 with PV

Projected annual utility costs: $797 without PV, $21 with PV

Annual energy savings compared to code-minimum house: 15,367 kWh without PV, 25,067 kWh with PV

Water Efficiency

Low-flow plumbing fixtures

Indoor Air Quality

Air infiltration rate: 0.97 ach50

Mechanical ventilation: 5.4-watt exhaust fan in laundry runs continuously at 30 cfm to meet ASHRAE 62.2 requirements. A 200-cfm supply air fan comes on automatically when the 400-cfm range hood fan is turned on.

Alternate Energy Utilization

Renewable energy: 9.7-kW PV system

Certification

DOE Zero Energy Ready

Northwest Energy Star Certified

EPA Indoor airPLUS

11 Comments

  1. User avater
    Dana Dorsett | | #1

    How does a 12" thick R26 SIP meet IECC 2012 for a roof?
    It's probably a typo- R46 instead of R26.

    A 12" thick SIP with an EPS core is nominally ~R46. With minimal thermal bridging of the internal splines it probably meets IECC 2012 on a U-factor basis, despite coming up a bit shy of the nominal R49.

  2. User avater GBA Editor
    Martin Holladay | | #2

    Response to Dana Dorsett
    Dana,
    Thanks for catching the typo. Yes, the roof SIPs are rated at R-46. The typo has been corrected.

  3. Robert Lepage | | #3

    Window U-Values
    What IGUs are they using to get U-0.097 and a SHGC of 0.62?

  4. User avater GBA Editor
    Martin Holladay | | #4

    Response to Robert Lepage
    Robert,
    GBA has been trying to get more information on the window specs from the builder; unfortunately, we haven't yet gotten that information. We'll update this page as information becomes available.

  5. Peter L | | #5

    Intus Windows
    The windows they used are Intus triple pane uPVC windows. The glass itself is Guardian glass and the glass energy ratings are as listed. They use Swiss warm edge spacers and Argon or Krypton gas in the IGUs. This is not a whole window + frame rating but a glass only rating.

    Here are the specs from the website:
    Thermal performance: R = 7.8*, Uw = 0.129* Btu/ (h.ft².F) with Ug = 0.088* Btu/ (h.ft².F) and Uf = 0.167* Btu/ (h.ft².F

  6. Robert Lepage | | #6

    European Standards
    Hi Peter,

    Thanks for that information. I don't suppose they have the test results under NFRC 100, eh? The website only seems to provide test results under EN standards, which explains why the CoG U-value appears so low.

  7. Greg Smith | | #7

    window specs
    Center-of-glass performance numbers are useful when comparing performance of similar IGU's that may vary in width, LowE coating, and/or gas fill.

    In my opinion, for a window company or salesman to offer IG CoG numbers as "window performance" is misleading at best and borderline dishonest at worst, but it is also not nearly uncommon enough.

    Once again it seems to be all about bragging rights.

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

    More on center-of-glass U-factors
    More more information on the difference between center-of-glass U-factors and whole-window U-factors, see All About Glazing Options.

    There are three reasons that European window manufacturers often fail to label their windows with NRFC labels -- the ones that show the consistent method used for U-factor labeling in the U.S.:

    1. NFRC labeling is voluntary, not mandatory.

    2. It costs money to put a window through the NFRC rating process.

    3. Center-of-glass U-factors look better to buyers (because they are lower) than whole-window U-factors, so European window manufacturers have little incentive to obtain the less deceptive, but less impressive, NFRC numbers.

  9. Peter L | | #9

    Will the real Delta T please stand up?
    Martin,

    You stated, "Center-of-glass U-factors look better to buyers (because they are lower) than whole-window U-factors, so European window manufacturers have little incentive to obtain the less deceptive, but less impressive, NFRC numbers."

    It's the last part of that statement that is somewhat harsh. In Europe there is no NFRC and the Euro standards apply to all Euro windows. It's not a "deceptive" practice, it is the standard in Europe so how are they being deceptive when they are using the European standard in Europe?

    NFRC American window energy performance testing and modeling assume a delta-T of 70°F (0° outside and 70° inside). In Europe a 35F winter delta-T is assumed for window energy performance. Even in a reasonably cold Northern European climate, this much more closely reflects the average delta-T during the heating season. This difference in assumptions affects the thickness of the air space in a window because a thinner window is less prone to the formation of convective loops. One can’t really fault U.S. manufacturers for building thinner windows. If they built thicker windows, they would test worse using the testing methods that are required by NFRC. But this means that outside of northern Alaska, where you might actually see a 70°F average delta-T during the heating season, US windows don’t perform as well as European counterparts.

    That's the reality of it. Where in the USA will you see a 70°F average delta-T?

    Most of the USA is in Zone 4 and Zone 5.

    Getting back to the NFRC ratings. Since European windows like Intus utilize the thicker windows as per European methods, it is penalized by NFRC. Even though the Intus windows PERFORMS BETTER in real life conditions, the NRFC penalizes them due to the inferior rating method that NFRC uses.

    So the problem is not Euro vs NFRC ratings but which rating represents real world data? It's clear, European standards work better because the NFRC ratings of a 70F Delta T is ludicrous because where in the USA does one see a 0F average outdoor winter temperature? Northern Alaska and maybe some interior Zone 7 areas like Northern Minnesota. Even a Zone 6 climate would not see a 0F average outdoor temperature.

    So who is being deceptive? NFRC using a flawed Delta T that results in windows that tests well but performs worse in the real life applications.

  10. Peter L | | #10

    European Standards
    We here in the USA are playing catch-up to European building standards, especially countries like Germany. It's 2013 and down the street they are slamming 2x4s together and stuffing R13 fiberglass batts into the walls, putting up cheapo dual pane vinyl windows that fail and leak in 3 years. Forget about air sealing a home, they laugh at you if you even brought it up. That is modern house construction. Some states are more progressive and implementing tighter codes but most areas in the USA are still using 2006 IRC & IECC.

    In 2010 there were approximately 25,000 certified Passive Houses in Europe. As of 2010 there were only 13 in the United States. Yes, more have been built since 2010 but the point is we here in the USA are 15 years behind the curve on energy builds.

    One can walk into a big box store in Germany and find high-performance triple pane windows sitting on a shelf while here in the USA we have cheap dual pane windows that are lucky to get R-2 and not fall apart in a few years.

    Andrew Dey in January 2014 wrote about this in a blog for GBA:
    https://lakesideca.info/blogs/dept/guest-blogs/visit-german-home-center

    European Standards on windows is not an attempt to be deceptive. I've seen and personally experienced windows fail in a short period of time that were NFRC or AAMA rated. Certification by those agencies doesn't equal quality.

  11. User avater GBA Editor
    Martin Holladay | | #11

    Response to Peter L
    Peter,
    I'm well aware that Intus's method for describing window U-factors conforms with European practices. You're right that this method of reporting is not deceptive when used in a European showroom.

    I'd like to step back and not focus on Intus alone, because I don't have the time right now to review Intus's marketing materials in depth. But it seems to me that any European window manufacturer that chooses to enter the North American market should go to the trouble of rating their windows according to the NFRC method. This approach will allow American buyers to compare the specs of the European windows being sold here with windows manufactured by Andersen, Pella, and Marvin.

    The failure of some European manufacturers to do this -- to get NFRC labels -- can result in deception when marketing materials don't clearly explain the difference between the whole-window U-factors with which American window buyers are accustomed and the center-of-glass U-factors used in Europe.

    Similarly, I would expect that, if Marvin Windows wants to open a showroom in Paris or Dusseldorf, Marvin should provide European window buyers with the U-factors they are used to.

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