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A 107-Year-Old Net Positive Victorian Retrofit

Even in chilly Minneapolis, a ‘standard’ house can be renovated for net-zero performance

Posted on May 10 2018 by Stewart Herman

In 2014, I learned about net-zero energyProducing as much energy on an annual basis as one consumes on site, usually with renewable energy sources such as photovoltaics or small-scale wind turbines. at the Minneapolis Home & Garden Show. Shortly thereafter, my wife and I purchased our retirement home and interviewed five sets of architects to compose the core of the design team. We settled on Marc Sloot of SALA Architects and Sean Morrissey of Morrissey Builders in St. Paul, both with considerable experience in sustainable design and construction. The result is our net-zero Victorian, showing that a standard city house on a standard city lot in chilly Minneapolis can be renovated to be net-zero in energy with no sacrifice in attractiveness, space, or comfort.

The design and permitting took more than a year, beginning in August 2014 through the end of 2013. We sought a variance in local zoning since the exterior walls on one side of the house were already over the side-yard setback from the property line, and then added 1 foot of exterior insulation, which moved the exterior wall surface even closer to the property line.

This kind of variance was unusual for the Minneapolis community economic planning and development board. We also requested approval for a 500-square-foot addition — just within the legal limits for the lot. After four months (late 2013-early 2016), approval was granted for both.

Construction process

Construction took 15 months (twice as long as we anticipated), from September 2013 through December 2016, although we were able to move in by late October 2016. Delays were due to adjustments in what needed to be done, scheduling problems, difficulties of constructing the envelope in the middle of winter, the level of detail required, particularly for interior Victorian style woodwork, and an insufficient number of skilled craftsmen.

The exterior walls required multiple layers — OSB, EPSExpanded polystyrene. Type of rigid foam insulation that, unlike extruded polystyrene (XPS), does not contain ozone-depleting HCFCs. EPS frequently has a high recycled content. Its vapor permeability is higher and its R-value lower than XPS insulation. EPS insulation is classified by type: Type I is lowest in density and strength and Type X is highest. blocks, window frame boxes, plywood sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. , furring strips and lap siding — all of which generated a more extended period of construction noise than is usual.

Four legs of the net-zero stool

Efficient insulation, effective air and moisture barriers, reduced energy consumption, and sources of renewable energy for both heating/cooling and electricity were the biggest drivers for the design and energy outcome of the home.

Typically, old houses are insulated by tearing out the interior plaster and putting in fiberglass batts, or punching holes in the walls and filling the cavities with cellulose. This house was insulated on the outside by attaching a 7 1/4-inch-thick layer of rigid insulation board (see Image #2 below). When added to the fiberglass insulation already in the stud cavities, we ended up with R-40 walls. The rigid foam used was expanded polystyrene (EPS), with 1,000 times less environmental impact than extruded polystyrene (XPSExtruded polystyrene. Highly insulating, water-resistant rigid foam insulation that is widely used above and below grade, such as on exterior walls and underneath concrete floor slabs. In North America, XPS is made with ozone-depleting HCFC-142b. XPS has higher density and R-value and lower vapor permeability than EPS rigid insulation.).

We also sprayed closed-cell spray foam between the rafters of a new roof (see Image #3 below). In tandem with fiberglass batt insulationInsulation, usually of fiberglass or mineral wool and often faced with paper, typically installed between studs in walls and between joists in ceiling cavities. Correct installation is crucial to performance. below, the R-60 worth of foam gives the roof assembly a total R-valueMeasure of resistance to heat flow; the higher the R-value, the lower the heat loss. The inverse of U-factor. of 80. A new foam chemistry has a much lower global warming potential than earlier spray foam formulations.

A tight house also needs to keep heat in the basement from leaking out. Typically, the foundation wall is insulated on the inside — not very effective — or by digging a deep, wide trench on the outside, which makes a huge mess. Our renovation was one of the first in Minneapolis to use a of insulating the foundation wall from the outside. Kinzler Construction Services removed a 4-inch-wide slice of dirt all the way down to the footings, then inserted a 1-inch foam sheet and 3 inches of sprayed closed-cell foam. The net insulating effect for the basement was R-30 while removing very little dirt.

The house has triple-glazed Andersen A-series windows throughout, further reducing heat loss.

Air and moisture tightness

Much heat and moisture is lost through leaky walls. We wrapped the house in a sticky membrane made by 3M (). This product is a vapor barrier. Twenty-five percent of the insulation is inside the 3M barrier, so moisture will evaporate back into the living space where humidity averages a comfortable 40-50%.

Seventy-five percent of the insulation is outside the 3M barrier but inside a Tyvek barrier. Air (and moisture) are allowed to circulate freely under the siding without entering the house. It's not quite the recommended 60%-40% split, but we've had virtually no moisture on window interiors through two pretty harsh winters

Our house is almost five times tighter than the building code, measuring 0.63 ach50. It is ventilated by an ERV (energy-recovery ventilator), drawing exhaust air from the kitchen and bathrooms. When the range hood operates, makeup air is drawn from outside past the refrigerator coils for more efficiency.

FormaldehydeChemical found in many building products; most binders used for manufactured wood products are formaldehyde compounds. Reclassified by the United Nations International Agency for Research on Cancer (IARC) in 2004 as a “known human carcinogen." is poisonous gas given off by some types of particleboard and some forms of insulation. Formaldehyde is a threat to health, and our house is so tight that inadvertent leakage would do nothing to reduce the threat. To combat this, we installed CertainTeed’s wallboard, which absorbs formaldehyde and renders it inert for a promised 10 years (see Image #4 below).

Reduced energy consumption

The house uses three heat pumps: a 3-ton geothermal (ground-source) heat pump, with a COPEnergy-efficiency measurement of heating, cooling, and refrigeration appliances. COP is the ratio of useful energy output (heating or cooling) to the amount of energy put in, e.g., a heat pump with a COP of 10 puts out 10 times more energy than it uses. A higher COP indicates a more efficient device . COP is equal to the energy efficiency ratio (EER) divided by 3.415. of 5.0; a heat-pump water heaterAn appliance that uses an air-source heat pump to heat domestic hot water. Most heat-pump water heaters include an insulated tank equipped with an electric resistance element to provide backup heat whenever hot water demand exceeds the capacity of the heat pump. Since heat-pump water heaters extract heat from the air, they lower the temperature and humidity of the room in which they are installed. ; and a heat-pump ventless clothes dryer. We disconnected our natural gas line and made the house all-electric. For heating and cooling, four linked geothermal wells were drilled in the 30-by-40-foot backyard. The wells are 250 feet deep, in a diamond pattern 10 feet on a side.

One lament of owners of old homes is that they must run the faucet a long time to get truly hot water from their centrally located water heaters. Our hot water typically arrives within five seconds, saving water and energy. To accomplish this, our plumbers installed a recirculation loop of thickly insulated (R-4) piping inside the building envelopeExterior components of a house that provide protection from colder (and warmer) outdoor temperatures and precipitation; includes the house foundation, framed exterior walls, roof or ceiling, and insulation, and air sealing materials.. A pump quickly moves hot water from the tank to the sinks. To save energy, the pump is activated by motion detectors — people entering the kitchen or bathrooms.

All lighting is LED, whether in traditional fixtures, cans, or in other locations.

Recycling heat is another way that we reduce energy consumption. In this house, heat is recycled in three ways. 1) The heat exhausted from bathrooms and the kitchen is used to warm incoming outside air through the ERV. 2) Excess heat from the geothermal heat exchangerDevice that transfers heat from one material or medium to another. An air-to-air heat exchanger, or heat-recovery ventilator, transfers heat from one airstream to another. A copper-pipe heat exchanger in a solar water-heater tank transfers heat from the heat-transfer fluid circulating through a solar collector to the potable water in the storage tank. pre-heats water in a pre-heat tank for the domestic water heater. 3) Our water heater is driven by a heat pump which sucks heat from basement air. It's three times more efficient than an electric-resistance water heater.

Energy is also saved through a new dryer design. Conventional dryers waste energy by heating with an electric coil and then venting warm exhaust outside at the rate of 135 cubic feet per minute. Our Whirlpool dryer () generates warm air with a heat pump. Instead of exhausting the warm air to the outside, it condenses the moisture from wet laundry into liquid. The warm liquid water then flows down a drain. No heat is lost to the outside air.

Renewable energy source

The house has 54 photovoltaic(PV) Generation of electricity directly from sunlight. A photovoltaic cell has no moving parts; electrons are energized by sunlight and result in current flow. modules (42 on the house and 12 on the garage, at 315 watts each) for a 17 kW capacity. This system was sized through modeling, which initially projected an annual consumption of 19,000 kWh. The actual 2016-2017 output was 17,000 kWh, more than enough to cover 12,000 kWh consumption in the first year.

The 42 PVPhotovoltaics. Generation of electricity directly from sunlight. A photovoltaic (PV) cell has no moving parts; electrons are energized by sunlight and result in current flow. modules on the house weigh 1,500 pounds. To support them, a new roof was built over the old crooked and weak roof. The new roof consists of I-joists and the space between them is filled with 10 inches of closed-cell spray foam. Including the 6-inch batts installed between the rafters of the old roof just below, the roof assembly achieves R-80. This spray foam employs a recently introduced blowing agent with a far lower greenhouse gas potential (GWP is 1) than other products.

Supporting all this new construction is a massive laminated beam running the length of the attic, which workers installed by hand (in six 300-pound pieces) rather than by crane. The beam rests upon steel posts which run down invisibly through the walls to thick footings in the basement (see Image #5 below).

Building operation

The home’s operation requires little involvement on a day-to-day basis. The ERV refreshes the interior air 20 minutes per hour. No thermostat setback is needed at night, and humidity remains at comfortable levels (40%-50%).

An system was installed to allow the internet-based monitoring of 24 individual electrical circuits throughout the house, while the performance of the solar system is also monitored over the internet through software.


Our aim was to create a low-maintenance natural Minnesota environment. The yard is bordered by hardscape frame — Versalok blocks capped with New York bluestone (which also is used for the front walk and terracing). Minnesota perennials, mostly drought-tolerant, cover 2,500 square feet of the yard. A three-zone drip irrigation system is installed to carry these 800 plants through a dry summer.

One-fifth of the yard is planted in Kentucky bluegrass, with no installed irrigation. Managing precipitation is another priority. The house keeps runoff — even from the heaviest of rains — from reaching the street and storm drains. The water is channeled into , perforated plastic barrels buried underground. These hold the water until it percolates back into the ground.


We have the satisfaction of knowing that we have rescued, renewed, restored, and repurposed a perfectly viable Victorian treasure in a way that preserves its character and demonstrates that a neighborhood can be revitalized without being reduced to a brownfield.

The house has achieved — and surpassed — net zero. The energy-conserving measures described here have kept the electricity consumption to 12,000 kWh for the first year — far less than the 17,000 kWh we generated from solar panels during the same time frame. Our house is therefore “net positive,” producing more energy than it uses.

This extra energy is sold to our local utility, Xcel Energy, at an effective rate of approximately 20 cents per kW hour. In our first year, the system produced about $3,000 worth of electricity, yielding a return of about 7% on the initial investment of $40,000 (after the federal tax credit).

This post originally appeared at the and is republished here with the permission of the author. Stewart Herman also is the author of

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  1. TK

May 16, 2018 7:54 PM ET

foam vs panels
by Sam Clarkson

So If i get good at spraying foam and then trim to an accurate depth, spraying would potentially be the more airtight option? (not that I'd be relying on foam to be my airtight membrane as such, but snug is better right?) Does it come down to time spent detailing the tight fit of panels vs the time spent trimming foam to an even depth, which is the better use of my time? Which is the better outcome?
If I get this Hotel i'll be approaching the NZ Passive House institute to use this as a training opportunity. It lends itself ideally for a study project. It needs EVERYTHING done to it.

May 16, 2018 11:59 PM ET

adapting insulation to the situation
by Stewart Herman

Exactly, Dana. Thanks for the granular explanation.

May 17, 2018 5:51 AM ET

Response to Sam Clarkson
by Martin Holladay

It's possible to use spray foam to insulate the exterior side of the wall of an older home, although the technique is rarely used because of the high cost of the spray foam. Here are links to two stories describing the process:

Deep Energy Makeover: One Step At A Time

Brand New Appearance and Performance for An Older Duplex

May 17, 2018 1:10 PM ET

Hot Water Re-Circulaton System vs. point of use electric?
by Judson Aley

For the hot water would it make sense to have a small on-demand electric water heater close to the point of use instead of the complexity of an electronic eye, circulating pump and related heat loss?

I live in a long narrow house, the utility room/hot water tank is 50’ from the master bath and it’s a long wait for the hot water. I’ve thought about putting something like this in a closet close to the master bath thinking it would provide the initial need for hot water and once the hot water arrived from the utility room boiler it would shut down the on-demand electric?

May 17, 2018 5:05 PM ET

Martin reply
by Sam Clarkson

Sorry to hijack the thread, but I'm looking to do an entire hotel, search Skotel New Zealand. At this scale i'm looking to buy an entire rig. But, I'm not the owner yet, and when i get there I'm going to start a thread for you experts to help me in that learning process! If you do search it up, you'll see there are entire wings and entire buildings to bury in foam (or whatever).

May 17, 2018 7:04 PM ET

Electric on-demand is a grid-disaster @ Judson Aley
by Dana Dorsett

At a 75F rise (35F in, 110F out at the sink tap) even 1 gallon per minute is about 11,000 Watts, and needs to be on a dedicated 50A/240V breaker. Even four of them adds up to 200A/240V of service to the house, and that's when not even using anything else!

Multiple point of source on-demand water heaters (or even one single whole-house electric tankless) almost never makes sense:

The grid infrastructure required to support large intermittent loads like that is a big cost adder to the distribution grid that we all have to pay for.

With the hot water in this case being heated at very high efficiency with a ground source heat pump, which makes the losses of the recirculation system pretty tolerable. The total electricity use is far less than the unleveraged efficiency of resistance heated hot water. Even at 99%+ efficiency for the on-demand water heater it will never come close to the ~400%+ efficiency of the ground source heat pump at domestic hot water outpu temps, even after distribution and recirculation losses.

In your case, a small point of use electric TANK can make sense. A 50' of 3/4" has about a gallon of water in it, so even a 3 gallon local tank kept at 140F would have enough dilution factor on the ~65-70F incoming water to deliver reasonable water temps until water from the main heater arrived.

May 18, 2018 6:39 AM ET

Response to Sam Clarkson
by Martin Holladay

I did some Googling as you suggested, and discovered that .

Considering the value of your investment, you obviously need to consult with architects, energy consultants, and general contractors familiar with New Zealand materials and methods.

For inspiration, you might want to read this GBA article: Solving an Ice Dam Problem With Exterior Rigid Foam.

That said, I don't think you should take any advice from an American web site. Get local help. Good luck.

May 18, 2018 10:35 AM ET

deep energy retrofits
by Stewart Herman

Thanks, Martin, for passing along articles about two deep-energy retrofits--the in Somerville, the other in Brattleboro. Given the idiosyncrasies of older houses, every project is going to be remarkably different. Little standardization possible. And owners likely are going to have to be heavily invested--not only in money but in knowledge, patience, etc. So this is likely never to be more than a niche trend, sad to say.
Still, I am curious--you seem to be tracking this. Any idea how many have been done, nationwide? I found a couple on the ILFI site, but those are only the ones that seek certification. I am particularly curious about the projects that aspire to net zero and are 100 years old more, but a wider net would yield an interesting nosecount as well.
Or is there a good source to go to for such information? Thanks in advance for any breadcrumbs you can point to.

May 18, 2018 10:41 AM ET

heating water at a distance
by Stewart Herman

Dana, you make a strong case against on-demand water heaters. Good to know.

I wonder then how well a recirc system would do at 50 feet distance? Obviously insulating the lines is needed. We wrapped our lines in R4 insulation. Would you recommend more?

By the way, our water heater uses an air-source heat pump (bolted onto the top of a conventional-looking water heater (although a separate pre-heat tank draws excess heat from the ground source heat pump that heats/cools the house). I am guessing the air-source is not as efficient as the ground-source, but perhaps not enough to be undercut your recommendation.

May 18, 2018 11:14 AM ET

Insulating recirculation loops @ Stewart Herman
by Dana Dorsett

If your water is being heated by burning $100 bills it's definitely going to be worth insulating a 50' recirculation loop to something greater than R4 (which is already greater than the code-min R3).

If the water is being heated with a tank-top heat pump at a COP of ~2, half the heat is either coming from a ground source heat pump at COP of 4-5-ish during the heating season, or actively reducing the cooling load during the cooling season. So maybe it's really only averaging 150% efficiency annually, not 300%+, that's still a LOT more than the sub-100% achieved by a tankless. Are you really going to lose 30%+ of the total heat in the distribution plumbing? (I doubt it, with a 50' recirculation loop.) With electricity that is in real time either coming from on-site PV in or drawn a local & regional grid that is rapidly decarbonizing, the case for going higher than R4 is pretty thin on both financial & environmental grounds.

All insulation has diminishing returns with increasing R, but with the geometry of cylinders working against it those returns diminish a lot faster with pipe insulation than with planes such as walls/roofs/floors. With pipe insulation on 3/4" or smaller pipe the total exterior surface area increases significantly with thickness, increasing the thermal coupling to the room, reducing the net effectiveness. Doubling the R value from R4 to R8 still cuts the rate of heat loss, but the reduction is far LESS than a reduction by half, the way it (nearly) would be for a wall, due to the substantially greater exterior surface area that comes with extra thickness at these small diameters.

May 18, 2018 11:17 AM ET

Edited May 18, 2018 1:47 PM ET.

Response to Stewart Herman (Comment #58)
by Martin Holladay

Lakesideca Advisor is one of the best available sources of information on deep energy retrofits. We have been reporting on this topic for many years, and there are lots of articles on GBA on the topic.

To get you started, see these articles:

Deep Energy Retrofits Are Often Misguided

The High Cost of Deep-Energy Retrofits

The History of the Chainsaw Retrofit

An Old House Gets a Superinsulation Retrofit

Remodel Project: Deep Energy Retrofit

Alex Wilson: Deep-Energy Retrofits

Brand New Appearance and Performance for An Older Duplex

Exterior Insulation for an Ugly Brick Building

A True Net-Zero Gut Rehab, New England-Style

A Leaky Old House Becomes a Net-Zero Showcase

Solving an Ice Dam Problem With Exterior Rigid Foam

Deep Energy Makeover: One Step At A Time

Video: Spray Foam Blankets a 100-Year-Old House

More Job Site Visits in Maine

A Deep-Energy Retrofit in Northwest Vermont

Jefferson City Deep Energy Retrofit

Wrapping an Older House with Rock Wool Insulation

Window Installation Tips for a Deep Energy Retrofit

A Deep Energy Retrofit Using Nailbase Insulation Panels

Mission Zero House: A Net-Zero Retrofit

A Practical Look at Deep Energy Retrofits

A German Deep-Energy Retrofit

Net-Zero Energy on a Mass Scale

The First Passivhaus Retrofit Certification in the U.S.

When Remodelers Carve Paths to Passive House

One Man’s Quest for Energy Independence — Part 1

Rebuilding a Mid-Century Dinosaur

From ‘Tea House’ to Tight House

A 100-Year-Old Energy Star Home

Michigan's First LEED Platinum Gut-Rehab

1970s Home Goes Net Zero

Foam Shrinks, and Other Lessons

Extending Window Openings for a Deep Energy Retrofit

Video Series: Exterior Insulation Retrofit — How to Install Foam On a Roof

Exterior-Insulation Retrofit — How to Choose Retrofit Details and Materials

Video: Deep-Energy Retrofit, Portland, Oregon

Part 1: What Is a Deep Energy Retrofit?

Deep Energy Retrofits, Part 2: Focus on the Envelope

Deep Energy Retrofits, Part 3: Apply the Energy Efficiency Pyramid

The Big Rewards of a Deep Energy Retrofit

Number Crunching on a Deep Energy Retrofit

All About Larsen Trusses

Study Shows That Expensive Windows Yield Meager Energy Returns

Learn the Real (Hard) Work of Residential Design

Making an Old Tract House Sunnier and More Efficient

Providing Outdoor Combustion Air for a Wood Stove

A Two-Home Demo for Deep-Energy Retrofits

Marc Rosenbaum: Moving to a New House

Blog Review: MinnePHit House

U.K. Victorian Finds Its Way to Passivhaus Performance

May 21, 2018 9:39 AM ET

deep energy retrofits
by Stewart Herman

Thanks, Martin, for forwarding such a compendious list of articles. What is to be learned, in aggregate?
1. Of the 20+ retrofits here, most do not involve seeking certification as net zero.
2. They are wildly different--in approach, in cost.
3. They require extensive planning, manual labor, in-course corrections as challenges arise.
4. Hands-on involvement by owner is the main way to keep down costs.
5. While the original project you seem to admire (Saskatoon--almost ten years ago!) was achieved at low cost, most of the subsequent ones were expensive--hence your disillusionment?
These are just some observations. On to a few generalizations:
a. A variety of approaches are being tried, and presumably will continue to be experimented with, given the different conditions evident in projects. Experimentation is good.
b. There likely will be no cookie-cutter approach to deep-energy retrofits which will permit cost-cutting through standardization and volume.
c. In the absence of soaring energy costs, deep-energy retrofits are likely to be undertaken mainly by committed owners and builders, rather than foster the growth of a new industry.
d. Since certification does not appear very popular (that too costs money!), we're not likely to get an accurate count of how many retrofits result in net-zero houses.
I offer these thoughts informally and tentatively. From your observations over the years, would you amend or disagree with any of these points?
Thanks again for providing all the links.

May 21, 2018 10:05 AM ET

Response to Stewart Herman
by Martin Holladay

You wrote, "While the original project you seem to admire (Saskatoon--almost ten years ago!)..."

In fact, the original chainsaw retrofit in Saskatoon occurred in 1982, which (if my math is correct) was 36 years ago, not 10 years ago. Here is a link to my article about that project: The History of the Chainsaw Retrofit.

You wrote, "While the original project you seem to admire was achieved at low cost, most of the subsequent ones were expensive -- hence your disillusionment?"

As I've written many times, I usually distinguish between weatherization work (usually defined as measures that are cost-effective) and deep energy retrofits, which are never cost-effective. I'm a big believer in weatherization. Deep energy retrofits -- not so much. My analysis and opinions are provided in this article: Deep Energy Retrofits Are Often Misguided.

May 21, 2018 10:14 AM ET

by Stewart Herman

With 'almost ten years ago" I was referring to your (2009) post, not the project itself. Sorry for the unclear reference.

The Saskatoon project was a pretty radical 'weatherization' project, if you want to call it that. What intrigues me about it is that it was presented as a single recipe for retrofitting all of Canada's aging housing. And it is beguilingly simple idea, and the proponents claim it works. That makes me wonder what happened to the concept. Have you heard of anyone else trying the same approach (poly wrap, with foam boards for insulation?)

May 21, 2018 10:27 AM ET

Response to Stewart Herman
by Martin Holladay

The chainsaw retrofit in Saskatoon was groundbreaking because it was the first time that an entirely new thermal envelope was installed on the exterior side of an existing house. The researchers who performed the work were unsure of whether the work would be cost-effective. In their report, they wrote that "costs for the total retrofit were high."

All of us in the energy-efficiency community salute Rob Dumont and Harold Orr because they were pioneers. They were also careful researchers who documented their work.

Almost every deep-energy retrofit since that first project in 1982 takes the same approach: Strip off the existing siding and roofing, and then install a new thermal envelope (including insulation and high-performance windows) on the exterior side of the existing sheathing. While the type of insulation and air barrier materials have changed over the years, the basic method has not. Rob Dumont and Harold Orr invented the technique.

Dumont and Orr did not find the technique to be cost-effective; nor have subsequent followers of the method like Paul Endrenkamp.

May 21, 2018 11:15 AM ET

DIY Savings
by Malcolm Taylor

Stewart commented that "Hands-on involvement by owner is the main way to keep down costs."

Given that labour is a significant part of all construction budgets, this is true of new construction too. However, when evaluating the cost effectiveness of a retrofit, or publishing the cost of any project, including the savings from work done by owners distorts the analysis, as it really just hides labour costs the owner didn't charge for.

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