Dr. Tom Marsik, Assistant Professor of Sustainable Energy at University of Alaska Fairbanks Bristol Bay Campus, and his wife, Kristin Donaldson, have built a small, 590 sf, 2 bedroom, 1 bath, Net Zero Ready home in Dillingham, Alaska. The Air Changes per Hour for this home based on a third party-verified blower door test came to 0.05 ACH@50 Pascals – the world’s most air tight home according the World Record Academy.

Dr. Marsik was kind enough to describe how he built this extremely air-tight, energy efficient home, which saves about $4500 per year in energy bills compared to a standard rural Alaskan home.

Zero Homes: Please describe how you attained such extremely low Air Changes Per Hour.

Tom Marsik: The main technique used to achieve this level of air-tightness was the framing technique, which I call the “box-in-a-box” technique. By having the internal “box” as almost an independent structure, there is an easy surface to work with, which we wrapped in plastic sheeting as a vapor and air barrier. Also, thanks to this barrier being on the outside of the inside structure, wiring and plumbing (except for the initial penetrations where they are entering the house) are run through the interior framing without puncturing the vapor/air barrier in places where the traditional cold-climate technique (vapor barrier right underneath the sheetrock) would have punctures (light switches, outlets, etc.). This way the vapor/air barrier is also much less prone to damage by occupants (hanging pictures, etc.).

Zero Homes: Please describe the wall and ceiling assembly in the context of the  “box- in-a-box” technique.

Tom Marsik: The inner wall and inner cathedral ceiling are made of 2×4 and 2×8 framing, respectively. 3/8″ plywood sheathing is applied to the outside of this framing. Plastic sheeting was applied on the outside of the plywood sheathing.  Fiberglass batts are in the framing of the inner wall and inner ceiling, and are covered with sheetrock on the inside. The plastic wrap extends underneath the floor to create an airtight plastic “bag” on all sides.

The double walls and double cathedral ceiling allow for ample room for blown-in cellulose between the outside of the inner wall/ceiling and the inside of the outer wall/ceiling. So in addition to the excellent air sealing, this “box within a box” allowed us to achieve very high R-Values: R-90 in the walls and R-140 in the ceiling. Here is a cross section of the 28″ thick wall assembly:

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Here is a cross-section of the box within a box construction with the continuous vapor barrier:

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Zero Homes: What kind of plastic sheeting did you use, how did you attach it, and what challenges did you face in attaching it and keeping it from ripping? 

Tom Marsik: Our air/vapor barrier is regular 6 mil polyethylene. It is on the outside of the sheathing (3/8″ plywood) of the inner structure, and it is simply attached by stapling (only at the seams; no attachment elsewhere).  The seams are sealed with an acoustical sealant (Tremco) and the staples go through the sealant. We then also taped the seams with red construction tape for a double seal (probably not really necessary, but easy to do).  Here is a picture of the seam between the floor poly sheet and the wall poly sheet (picture taken inside the wall cavity):

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The challenge was in building the double-frame building (you are basically framing two houses), but once that is done, installing the plastic sheeting as an air/vapor barrier itself is fairly simple. I don’t remember a single rip in it, but if it did rip, I would probably just tape it.

Zero Homes: How did you handle and seal wiring, plumbing, and other penetrations through the wall assembly?

Tom Marsik: As I mentioned, the wiring and plumbing is mostly inside the vapor barrier (in the 2×4 framing). There are a few penetrations (not very many) through the vapor barrier. They are sealed primarily with bituthene (applied with a heat gun to make it stick well). As an example, here is a picture showing how we sealed the HRV vents where they penetrate the vapor barrier:

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Zero Homes:  What are the risks of condensation occurring on the plastic sheeting?

Tom Marsik: Because of the massive insulation on the outside of the plastic vapor barrier, the temperature of the vapor barrier is above the dew point in basically all situations, thus there is basically no chance for condensation. This assumes proper operation of the HRV, which is taking some of the moisture that has been generated inside the house to the outside (and some of the moisture condenses inside the HRV’s heat exchanger and goes down the drain).

Zero Homes: If your wall thickness was reduced to, say, 12″ for the purposes of use in the northern parts of the lower 48, would there be problems with condensation on the plastic sheeting?

Tom Marsik: A 12″ thick double-stud wall that has plastic on the outside of the inner 2×4 stud wall will have more than 2/3 of the insulation’s R-value on the outside of the vapor barrier and less than 1/3 of the R-value on the inside. That would work well from the perspective of not having condensation in the wall. The 2/3, 1/3 rule is a rule of thumb for Alaska. In warmer climates you can get by with even less than 2/3 of the R-value on the outside of the vapor barrier because the vapor barrier will be staying warmer (thus less chance for condensation) thanks to the warmer outdoor temperature.

Zero Homes: How much extra time and cost was involved in this air-sealing endeavor compared to other techniques?

Tom Marsik: The actual plastic wrap installation is, I think, less costly and less time consuming than most other techniques, mainly because it does not involve the extra work of sealing electric outlets, switches, etc. When it comes to framing the box-in-a-box structure, it’s a different story, though; there is a lot of added cost and time. But that cost and time can’t be attributed just to air sealing because it has other benefits such as minimizing thermal bridging and providing more space for insulation.

Zero Homes: What was your goal and why did you seek such a low ACH50?

Tom Marsik: Our goal was to build a super energy efficient and durable home. Our intention was to demonstrate that we can build super efficient homes even in remote and frigid rural Alaska, where access to materials (and other resources) is very limited. “Keep it simple” was an important principle of our project. So we used common materials as much as we could.

Achieving a high level of air tightness has an effect on both energy efficiency and durability (due to reducing the opportunities for condensation within the wall). With that being said, is it necessary to go down to 0.05 ACH50? Probably not. Our intention was not to build the world’s tightest house, our intention was to build a super energy efficient and durable home, and air-tightness is an important part of that. I personally consider the Passive House’s 0.6 ACH50 criterion a useful guideline and that’s what we were shooting for with our project – we wanted to be below 0.6 ACH50. This standard is difficult to achieve in small homes because of the high ratio of the area of the building envelope to the volume of the house. That’s why we took extra precautions – better to be on the safe side because you won’t know until the blower door test whether or not you did the air-sealing right.

Zero Homes:  How can people learn more about how your home was constructed?

Tom Marsik:  Please visit Alaska Energy Wiki for a slide presentation, an Alaska Building Science News article, or flicker pictures  to learn more about the construction of our home.

Zero Homes: Thanks so much Tom for setting this wonderful example of how homes can be made more airtight! 

Please address comments and questions on this blog to: joeemerson(at)zerohomes.org

 

 

 

 

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Depending on the energy incentives, rebates and tax credits available in different states cost-effective Zero Energy Homes (ZEHs) may cost as little as 5% more than a comparable standard home. Yet, the total cost of ownership of a ZEH can be considerably less than for a comparable standard home. The total cost of ownership includes the mortgage on the cost of the home (land and construction costs), and the continued expenses for maintaining and operating a home, such as space heating, cooling, water heating, lighting, appliances, and plugging in all those appliances and electronics!

Designers, builders, lenders, realtors and homebuyers rarely address the total cost of ownership of a new home. Yet, the total cost of ownership, not dollars per square foot, should be the primary financial yardstick used by all stakeholders when evaluating the value of different homes. To show why this is so important, I examined the total cost of ownership of two ZEHs in Bend Oregon, which were equivalent to neighboring homes in their size, external appearance, interior finishes, and appliances.

The average sales price for these two ZEHs was $420,000. The average added costs to get to net zero compared to building the same home without the energy saving features needed to get to net zero was $12,500, or 4%. The cost of the land, the cost of construction, and the added cost to get to zero (less all available federal and Oregon State tax credits and available energy related incentives) were rolled into a 30-year fixed mortgage with a 3.5% APR and a 20% downpayment. The monthly mortgage payment for the ZEHs averaged $1,509, and the monthly mortgage payment for the similar standard homes was $1,464, a difference of $45.00 higher per month for the ZEHs. The cost of energy for each home came to $120 for the yearly grid hook-up fee for the ZEHs, and $1920 yearly electric costs for the comparable standard home built to code at 2011 electric prices in Oregon.

The graphs below compare the average total cost of ownership for the two ZEHs with comparable standard homes over a 15-year period: first, with electric prices increasing an average of 3% per year (based on projections for future electric prices in Oregon), and then with electric prices increasing an average of 4.4% per year (the 20 year average yearly electric rate increases in Oregon from 1990 to 2010).

[Please Click here to see a graph of savings with 4.4% projected electric rate inflation per year]

The graphs show that ZEHs produce significant cost savings of $1260 during year one and that the cumulative benefit in energy cost savings for the ZEHs over 15 years was $25,378 @3% inflation and $29,033 @4.4% inflation* – savings which could be invested.  In the standard home, the cumulative energy cost burden over 15 years was $35,278 at 3% inflation and $38,933 @4.4% inflation – a significant loss of family income.

Based on the total cost of ownership, even though the initial square foot costs are somewhat higher, Zero Energy Homes cost less for the homebuyer than a standard home, starting at year one. Anyone who can afford a home can afford a Zero Net Energy Home.

Glenn Haupt is the owner of Solar Craft Design located in Bend, Oregon. His work focuses on the design of low energy, healthy green homes.  He is a Certified Passive House Design Consultant, Certified Sustainable Building Advisor, Energy Consultant, and blogger.

*The comparison in these graphs is based on one neighborhood in Bend, Oregon. Results may vary as tax credits and energy incentives vary from state to state, current electric rates and projected inflation rates for electricity vary, and climate and costs of construction vary from region to region.

 

In today’s market, would you ever consider buying a car that gets 12 miles to the gallon?  Would you even consider designing, building or selling a car that gets 12 mpg? I believe 100% of us would respond with a resounding NO. Why? Because we all know there is a great selection of stylish, comfortable, reliable, and safe cars that are reasonably priced, and get up to 30 miles to the gallon, and others like hybrids that exceed 50 miles per gallon, and electric vehicles that approach 100 miles per charge.  This generation of fuel-efficient cars offers great performance and is fun to drive.  Even if you do a modest amount of driving, the money will favor a very fuel-efficient car, and the payback will be even faster if you drive a lot. Buying a very fuel-efficient car makes good financial sense.

Does it not stand to reason then that homes should be designed and built to be beautiful, durable, functional, and very fuel-efficient?  Shouldn’t they be healthy and comfortable to live in, and be as economical to operate as the latest greatest hybrid or plug in electric vehicle?  How about a home that does even better?  How about a home that produces as much energy from renewable energy sources as it consumes from the utility provider in the course of a year and over the life span of the home!

These homes, called Zero Net Energy Homes (ZNEH) or Zero Energy Homes (ZEH), are being built today across the United States, by pioneers in the building industry who have developed a strong business case for a way of building that provides immediate and long-term benefits to the health, comfort, and financial security of the homeowner – all of this, while benefiting the environment through zero net carbon emissions.

Wouldn’t we all want to have an exceedingly low or zero monthly home energy bill, forever?  That makes great financial sense to me! Wouldn’t it be a great bonus, that such a home is also healthier and more comfortable to live in and helps protect the environment during our lifetimes and the lifetimes of our children and their children’s children?  That sounds great to me!

Making the Case for Zero Energy Homes Becoming the Norm in Home Construction 

The mission of this blog and associated website http://www.zerohomes.org/ is to provide education and outreach to all stakeholders in the home building industry so that affordable, market comparable, Zero Net Energy Homes and near zero energy homes become the norm for home buyers, designers, lenders, realtors and home builders.  Below, I have formulated a partial list of the benefits and advantages of building, owning, and/or living in a Zero Net Energy home.  We will be exploring these and other benefits of Zero Net Energy Homes in much greater detail during future weekly blog posts, not only from a potential homebuyer perspective, but also from the perspective of builders, designers, lenders, and realtors with the purpose of confirming that there is a strong business case, as well as a strong health, comfort and environmental case, for the rapid increase of ZNEH construction and sales.

 The Benefits of Zero Net Energy Home Construction 

  • Comfort: Zero Net Energy Homes provide a high degree of thermal comfort by maintaining stable interior temperature and eliminating drafts by employing airtight, but breathable construction, by using high insulation levels, and by using high performance windows and doors.
  • Health: Fresh filtered air is continuously supplied while stale air is expelled through a high performance ventilation system, providing optimum indoor air quality compared to traditional ventilation systems.  This is very important for people who suffer from allergies and chemical sensitivities.  Living in a ZNEH with a highly effective ventilation system allows both the adults and children to breath air that is healthier, resulting in fewer missed work or school days due to respiratory issues.
  • Quiet: A well designed ZNEH is very quiet thanks to thicker walls and better insulated and air-tight windows and doors, providing a more relaxing home environment.
  • No Net Energy Bills: ZNEHs provide protection against future energy price increases and inflation.  Money that you would have spent on heating, cooling, and lighting a conventionally built home can be redirected to your personal well-being and financial savings plan.  Therefore, ZNEHs not only promote energy independence, but also provide for a sense of personal and financial empowerment.
  • Solid Investment: The market demand and resale value of truly high-performance green homes and Zero Net Energy Homes have a great return on investment.  First of all, they are very well built, comfortable and healthy to live in. Secondly, as the price of energy goes up potential buyers will place a high value on having a home that has no energy bills.
  • Affordable: ZNEHs cost no more than comparable homes built to code based upon the total cost of ownership.  In a well planned and executed ZNEH, the “perceived” extra initial costs for construction and energy systems can be rolled into the mortgage.  The resulting small increase in the monthly mortgage payments are balanced out by having little or no energy bills. If the added cost is not rolled into the mortgage, the pay back on the extra costs can be as short as 5 to 8 years depending on your energy use, local energy costs, available state tax credits, rebates and incentives.   After the payback period, your monthly cost of living will be significantly lower and considerably more affordable for the long term than a conventionally built home.
  • No Carbon Emissions: ZNEHs are “legacy” buildings that are healthy for the planet, for your family, and for the generations to come.  The excess electricity your ZNEH produces from renewable sources supplies your neighbors’ traditionally built homes with energy from a clean renewable source instead of from a carbon producing electric utility.
  • The New Normal:  ZNEHs look like any other home, are easy to operate and live in, and use standard building techniques and materials that have proven reliability. While ZNEH owners usually make a point of using energy conservatively, life in a ZNEH is like living in any other home, except that it is healthier, more comfortable and less expensive to operate. Look to ZNEHs becoming the new “normal” in home construction in the decades ahead.

This blog can only be complete if this discussion engages all stakeholders in the industry; therefore our intent is to reach out to lenders, realtors, and appraisers, in addition to designers, builders and homebuyers, with regards to the financial value-added ZNEH construction offers compared to traditional code minimum homes.

We will interview owners who currently live in zero net energy homes; we will interview builders and designers, and realtors involved in ZNEH construction and sales; and we will track the construction of new zero net energy homes under construction, and present their stories along with the strategies that were employed on the path to reaching the ZNEH goal.  We will be transparent and honest about the process so we all can benefit from our lessons learned.  And as we are making the Case for Zero Net Energy Home Construction, our goal is to provide you with the information and tools you need for making the case for Zero Net Energy Homes to your clients, colleagues, and friends.

 As I bring this debut blog post to a close, I hope you will join us here, like us on Facebook, follow our tweets, and subscribe to news feeds via RSS, and sign up for our monthly e-newsletter at http://www.zerohomes.org/ We appreciate in advance your input and perspectives, and recognize there are many paths for achieving the ZNEH goal.

We hope to convince you, and inspire you to share with friends, colleagues and potential homebuyers that….The Zero Net Energy Home Building Revolution is underway! It’s time to jump on board!

Glenn Haupt is the owner of Solar Craft Design located in Bend, Oregon.  His work focuses on the design of low energy, healthy green homes.  He is a Certified Passive House Design Consultant, Certified Sustainable Building Advisor, Energy Consultant, and blogger.

 

Carter Scott of Transformations, Inc has built numerous Zero Net Energy Homes in Massachusetts, ranging from custom homes, to development homes and to very affordable low income Zero Energy Homes. He shares some of what he has learned about building Zero Energy Homes in this interview. For articles written by Carter on his Zero Energy Homes go to Zero Energy Building Practices under the “Professionals” button.

What year did you build your first Zero Net Energy Home?

Carter Scott (CS): We built our first Zero Net Energy Home in 2008

How many Zero Net Energy Homes have you and your company, Transformations, Inc., been involved in building?

CS: We have built 11 highly insulated airtight homes with solar photovoltaic systems that have Home Energy Rating System (HERS) Index ratings ranging from -9 to +8 (which were Zero Net Energy Homes or Zero Net Energy Attainable).  We have another ten, which should be in the same range that we are currently building now. There are a total of an additional 90 Zero Energy Homes or Zero Energy Attainable Homes in this range that are in various stages in the development pipeline.

Do the homes with a HERS rating above 0, function as Zero Net Energy Homes if the occupants are energy efficiency oriented?

CS: I have had a home with a HERS 2 come in with a surplus of 1,574 kWh of energy over a yearlong time frame.  There is some thought that all homes under HERS 10 are Zero Energy Attainable and that the homeowner’s habits and the building’s specific energy efficient attributes will dictate whether they are net zero energy homes over time.

How much higher have the building costs been for the average Zero Energy Homes you have built compared to the costs of a similar homes built to code?

CS: We have gotten the cost down to about $5 per square foot over the code home.  This is with a leased photovoltaic (PV) system. The average solar photovoltaic system costs about $25 per square foot when you do the math. In Massachusetts, the Solar Renewable Energy Credits, the 30% Federal tax credit, the $1000.00 state tax credit, and the electric energy generated, all translate into a pay back of about 6 to 7 years for the solar PV system.

Which of your homes has had the least cost premium for becoming a Zero Energy Home?

CS: I would say the smallest homes in an absolute dollar basis and the larger 3 and 4 bedroom colonials in a marginal cost per square foot basis have the lowest cost premium of all our Zero Energy Homes.

Has the relative cost premium for Zero Energy Homes gone down as you have gained experience since 2008?

CS: Yes

What have you learned to do differently that has brought the cost down?

CS: The Navien instantaneous tankless hot water heaters have been very cost effective.  We have also learned to use the low density (open cell) foam and cellulose as much as possible while minimizing the more expensive high density (closed cell) foam.

In your experience in New England, which insulation material and R-value have you found to be most cost effective for the walls, floors and ceilings of your Zero Energy Homes?

CS: For under the slab in the basement, 2 inches of the blue rigid foam (R-5 per inch) have worked well.  For the basement walls, 3.5 inches of high density foam (R-6 per inch) with a fire coating paint applied.  For the above grade walls, either 12″ of cellulose or 12″ of low density foam.  We have gotten a great price from our insulating contractor, where the price of the low density foam (R-3.8 per inch) is the same as we would pay for cellulose (R-3.5).  For the attic we use 18″ of cellulose for a total R-Value of 63.

What are the average Air Changes per Hour  (ACH@50 Pascals) in your Zero Energy Homes?

CS: Our average blower door test is about 1.0 air changes per hour at 50 Pascals (ACH50).  Our lowest was 0.50 ACH50.

Which air sealing techniques have you found to be most cost effective?

CS: We have found that a triple system works best: 1.The Zip System (sheathing with an air barrier built into it) on the exterior walls;  2.The low density spray foam, and  3.The air sealing of the dry wall on the inside.

What Window to Floor Area (WFA) are you using in your Zero Energy Homes?

CS: The Window to Floor Area ranges from about 8 to about 12 percent.

Which insulated windows have you found to be most cost effective for Zero Energy Homes?

CS: We are now using the Harvey Tribute line, which is a triple pane window with Krypton gas and has a U-Value of around 0.20 depending on the size.

Since Zero Energy Homes are so air tight and ventilation systems are needed which heat the incoming fresh air with the warm stale air that is being exhausted from the building; what experience have you had with Energy Recovery Ventilation (ERV) or with Heat Recovery Ventilation (HRV) systems that are designed to supply this pre-heated fresh air?

CS: We have tried many different ways to ventilate our homes.  They range from simple exhaust only Panasonic fans in the bathrooms to a full Heat Recovery Ventilation system.  In high radon areas of the country, one must be careful not to pull in radon from under the slab in a bathroom exhaust only system.  A passive radon mitigation system (a LEED requirement in high radon areas) including sealing a layer of plastic under the slab is critical in this regard.  The more expensive balanced ventilation is achieved with the HRV and ERV systems.  We have installed the LifeBreath system and both the Fantech 704 and the Fantech 1504. The exhaust-only Panasonic fan model FV08VKS2 has been the most cost effective. It runs on 30 CFM with a boost to 70 CFM. Two of these exhaust-only fans usually meet the Energy Star ventilation requirements for a home.

How have you used passive solar heating or heat tempering in your Zero Energy Homes and how significant has it been?

CS: Yes, we have used passive solar heating in many of these homes.  We did a study a few years back and found that putting the garage on the North side of the home and having a couple extra windows on the South side saved about 5% of the home heating and cooling loads.  Some of the models have additional glass in the south, minimal glazing in the North, East and West, and overhangs on the Southern glass to minimize the summer heat gain.  This increases the solar heating and provides additional savings.

Have you found that using an interior thermal mass to enhance passive solar heating is cost effective.

CS: Yes, but only if homebuyers want to have slab on grade with a colored polished concrete as their floor surface.

What heating system have you found to be most cost effective?

CS: The Mitsubishi mini-splits have been fantastic.  The newer dual stage, inverter driven heat pumps cost us about $2850 installed, as part of a volume deal arrangement.  The model number of the indoor unit is MSZ-FE12NA and the model of the outdoor unit is MUZ-FE12NA.  We have used anywhere from 1 to 3 of the systems to heat and cool a home.

From your experience building Zero Energy Homes, which energy saving measure or measures have you found to be the most critical to making a Zero Net Home affordable?

CS: The super insulation and air sealing of the shell combined with a leased PV system.

What has the selling price range been for your Zero Energy Homes?

CS: Our Zero Energy Homes range from a very cost effective $125,000 to custom homes that are worth about $1.5 million. In Massachusetts, we have an affordable housing law that helps developers build more affordable homes.  Prices of these homes have been $125,000 to $145,000 in Easthampton, MA and $168,000 to $195,200 in Townsend, MA.  They are deed restricted and available only to buyers making less that 80% of the median area income.  We are building “Workforce Housing” for MassDevelopment in Devens, MA.  The homes there start at under $350,000.  There are no income restrictions, just a base price restriction.

The market rate Zero Energy Homes in the Massachusetts developments in Townsend, Princeton, and Easthampton tend to be in the $299,900 to 429,900 range depending on the model size and customizations. The custom Zero Energy Homes can range from $140 to $250 per square foot to build plus the cost of the land.

What kind of premium are buyers willing to pay, if any, for a Zero Energy Home compared to a similar home built to code?

CS: The premiums a buyer is willing to pay for a zero energy home vary from just a few percent to 30% or more.  At the lower end of the spectrum the photovoltaic (PV) systems are leased.  At the higher end of the spectrum the homes tend to be custom, and the PV systems are purchased.

Thank you so much Carter. You are a true leader in the Zero Energy Home movement. What you are doing is a wonderful inspiration for both homebuilders and homebuyers who are committed to creating a sustainable world.

CS: You’re Welcome – it has been a pleasure Joe. Thank you for helping get this information on Zero Energy Homes out to the public