Image Credit: Daniel Ernst
Image Credit: Daniel Ernst Once the Zip System sheathing is taped, it acts as a water-resistive barrier (WRB) as well as an air barrier.
Image Credit: Daniel Ernst A layer of OSB-colored nailbase was installed on top of the green Zip sheathing.
Image Credit: Daniel Ernst The ceiling air barrier consists of taped OSB. Strapping was installed under the OSB to create a service chase for wiring.
Image Credit: Daniel Ernst The "innie" windows have careful exterior detailing to direct rainwater away from the vulnerable window opening.
Image Credit: Daniel Ernst Transfer grilles help equalize pressure imbalances between bedrooms with closed doors and adjacent common areas. However, they won't do much to equalize temperature imbalances unless a fan is installed to create a pressure imbalance that forces air movement through the grilles.
Image Credit: Daniel Ernst The energy-recovery ventilator (ERV) hangs from the ceiling of the laundry room.
Image Credit: Daniel Ernst As long as the weather isn't too hot, the ceiling fan in the family room can be used to keep people cool without operating the air conditioner.
Image Credit: Daniel Ernst First floor plan.
Image Credit: Adam Cohen Second floor plan.
Image Credit: Adam Cohen
This custom home, a PHIUS+ certified project, disproves the notion that energy-efficient houses are cost-prohibitive
When the time came for Jason and Stephanie Specht to find a builder, they started out with high ideals. They wanted a builder who wouldn’t skimp on the quality of construction and who wouldn’t charge an exorbitant fee.
Since this was their first time building, there were a lot of unknowns and a lot of questions: As clients, would they be able to customize plans? Select materials and finishes? Could they realize their budgetary goals? Did the builder have a good reputation? Would the house be energy efficient?
Most of all, they were looking for a builder they could trust.
It was a difficult prospect, and their first efforts proved disappointing. After months of learning about the marketplace and figuring out the possibilities, they settled on Structures Design/Build. It was a business that offered custom plans and construction management, one that could take their project from concept to completion.
During their first consultation, Adam Cohen, a principal at Structures Design/Build, asked them if they had considered Passivhaus. (For more information on Adam Cohen, see Passivhaus Practitioners Share Their Success Stories.) Like many people, they had not yet heard of the Passivhaus standard. And, they assumed that energy efficiency was out of their reach — that it was just too expensive.
Reaching cost parity
Adam was quick to present a different point of view. On the contrary, he argued that constructing a Passivhaus wasn’t necessarily any more expensive than constructing a house to meet the existing energy codes. He told them that although their initial capital investment would certainly be larger, their monthly outlay would be the same. In short, Adam believed that by creating an optimized Passivhaus design, they could achieve cost parity with traditional construction.
What is cost parity? Literally, it means equal price. The phrase is often used to evaluate the performance of a new business (i.e. a new manufacturer). Economists say that a business achieves cost parity when they can produce a comparable product at a comparable price. In theory, it doesn’t matter if it is a commodity, a product, or service, the question is whether or not something is truly cost competitive.
In the context of Passivhaus construction, it is the idea that a builder can leverage their knowledge and experience to produce a Passivhaus at a price equal to standard construction, if the energy costs are included in the calculation. It is the idea that the additional capital costs of Passivhaus construction pay for themselves through savings in your monthly utility bill.
Research, research, and more research
Energy-efficient construction that was cost-competitive? What was not to like? Although the Spechts thought it was a great idea, they wanted to learn more about the Passivhaus concept. Jason started researching — and researching. He read the book, Recreating the American Home: The Passive House Approach, by Mary James. He studied the details of other residential Passivhaus projects, and spent countless hours on the Internet. In the process, he learned an entirely new vocabulary.
When the Spechts finally settled with the idea, they met with Structures Design/Build at the building site. And so began the process of designing a Passivhaus. Over the next few months they worked through multiple options: they finalized decisions on foundation type, building size, floor plan, and exterior style. The house would include an attached garage for vehicles, storage space for the canoe and other outdoor equipment, and provide a space where Jason could complete welding projects.
When the building process began, the research didn’t stop; it just took on a different dimension. Since Passivhaus projects often use new materials and techniques, Jason and Stephanie continued with their research and project involvement: they wanted to be sure they made informed decisions along the way.
Securing a loan was easier than expected
Jason worked at a local credit union. And even though he had a solid understanding of residential mortgages, and how to secure a loan at a good rate, he worried that it would be a troublesome process. He attempted to find a bank that offered EEMs (Energy Efficient Mortgages), and prepared to argue the merits of the Passivhaus concept. What he found was disappointing: loan officers were unaware of EEMs, even if their company offered them in their mortgage service portfolio.
In the end, he met a loan officer at a local bank that spoke his language, someone who valued energy efficiency and conservation. And all that worrying was for naught. The building plans were appraised at a value that was equal to the construction contract price — even without figuring in the utility bill savings. This was a pleasant surprise, and confirmed the idea that energy-efficient construction could be cost-competitive.
Now they were ready to break ground and start building.
Build your house on solid foam
Structures Design/Build specified an insulated slab — sometimes called a raft foundation. (For more information on raft foundations, see “Foam Under Footings.”) But unlike most raft foundations, this design incorporated a thickened edge. This had several benefits. One, the only proprietary piece of EPS foam was the integral footer; the majority of the slab could be insulated with standard sheets of EPS foam (readily available in most markets). Two, the slab could be poured at a standard thickness, reducing the amount of concrete required for the foundation.
It was a win-win situation, with lower costs, less shipping, and lower embodied energy.
Rigid air barriers rule
Zip sheathing and tape created the wall air barrier, and standard OSB completed the assembly on the second floor ceiling. The Zip System is gaining traction in the U.S. marketplace and is now commonplace in many locations. It doesn’t take long for a framing crew to install and detail this system to create an excellent air barrier.
Adam wanted to perform blower-door tests at various stages in the construction process. He conducted the first test when the airtight sheathing was first sealed, but before the framing crew cut the window and door openings. This multistage testing protocol helped him quantify and isolate the leakage paths, and later, determine the effectiveness of other air barrier components (i.e. window frames and utility penetrations).
Down come those thermal bridges
The framing crew built a fairly common structure — 2×4 studs, 16 inches on center, with solid lumber headers. They used open-web floor trusses for the second floor (providing a cavity for plumbing and ductwork) and engineered trusses for the roof.
So at first glance, it didn’t look like a Passivhaus structure. However, they later installed 6-inch-thick nailbase insulation over the entire wall, including the gable ends. This brought the nominal R-value up to R-37 and created a wall that was free of thermal bridges.
They later installed a deep layer of cellulose insulation above the second floor ceiling to finish the thermal enclosure.
Small heating and cooling loads
Mechanical ventilation is provided by an energy-recovery ventilator (ERV). The ERV is equipped with a heat-exchange coil on the fresh air inlet; this water-to-air coil is tied into a ground source loop (a plastic pipe buried in a horizontal trench). It is designed to temper the incoming airstream and reduce the temperature difference between exhaust and supply.
A ductless minisplit heat pump covers the peak summer and winter loads; the unit’s indoor head is located high in the stairwell and services both levels.
Transfer grilles help reduce pressure differences between the bedrooms and adjacent common areas, and encourage room-to-room mixing when the doors are shut. (For more information on transfer grilles, see Return-Air Problems.) But according to the homeowners, an open door definitely reduces heat build-up during the hottest summer nights; it also provides the greatest comfort level.
What you don’t see is what you get
Whether the impression is accurate or not, in the U.S. there is a pervasive idea that a green home requires weird architecture, recycled materials, and lots of high-tech gadgetry. Jason and Stephanie often found that it was difficult to explain the Passivhaus concept to friends, family, or site visitors. People touring the house wanted to see all of the innovative features — but in fact, there wasn’t much to show: most of the innovation was hidden behind the siding or the drywall.
Yes, the solar thermal system was visible out front, but the water heater looked entirely ordinary. There was a small black box in the utility room (the ERV) — but that was nothing to get excited about. And visitors could open the windows, admire the depth and heft of the triple-pane windows … but there wasn’t much else to see.
Perhaps it is a cultural artifact, or just human nature, but most people don’t get enthusiastic about air barriers, thick insulation, or low energy bills. The Specht family does. And they are even more excited about the fact that they built a high-quality house—an ultra-low-energy house — without blowing their budget.
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Lessons Learned
• Get involved! Although they were building a very passive house, the Spechts were very active in the design and build process. This gave them a sense of ownership and control, and contributed to the overall success of the project.
• Material choices had a bigger financial impact than the decision to build to the Passivhaus standard. Fiber-cement siding, hardwood and tile floors, solid surface countertops, and quality fixtures all cost more, period.
• Consider how volunteer organizations can help. A local club, the Roanoke Renewable Energy Electric Vehicle Association (REEVA), installed the solar thermal system — without charge. That’s community activism at its best.
• There is a learning curve with new products and technologies. It took some trial and error to learn how to best operate the minisplit heat pump: during the cooling season they found that letting the unit work longer at low speed provided greater comfort. Also, the Klearwall windows required adjustment by a factory representative. (I should note that these were among the first Klearwall windows shipped to the U.S. market).
• The solar thermal system generates a significant amount of heat inside the laundry room. On a warm and sunny day, the closed loop pump becomes a miniature radiator (i.e. loop temperatures reach 150°F). This is undesirable in the summertime. Placing the water heater in the garage would resolve this issue.
— Daniel Ernst is currently starting a design/build firm, Promethean Homes, in Steele's Tavern, Virginia. He posts regular blogs on his company's web site.
General Specs and Team
| Location: | Climate Zone 4A — Thaxton, VA |
|---|---|
| Bedrooms: | 3 |
| Bathrooms: | 2.5 |
| Living Space: | 1808 |
| Cost: | 150 |
| Additional Notes: | $150/sf includes septic, well, and some site work |
Designer: The Structures Design/Build team Builder: The Structures Design/Build team
Construction
Foundation: Modified “raft” foundation (monolithic slab)
Slab Insulation: Two staggered layers of horizontal EPS foam board (R-18) under entire slab; molded EPS forms at perimeter.
Wall frame: 2x4 studs, 16” on center, with solid lumber headers
Wall sheathing: Zip System sheathing
Wall insulation: R-13 fiberglass batts between studs and 6-in.-thick EPS nailbase insulation (R-37) on exterior of Zip sheathing
Wall air barrier: Zip System sheathing and tape
Siding: James Hardie HardiePanel fiber-cement siding installed over Home Slicker
Exterior trim: MiraTEC composite board trim
Windows: Klearwall windows with triple glazing (R-7)
Roof frame: Truss construction to create an unconditioned ventilated attic
Roof sheathing: 5/8” OSB
Ceiling insulation: Cellulose (R-60) on attic floor
Ceiling air barrier: OSB, sealed with duct mastic and tape
Roofing: Asphalt shingles
Energy
HERS Rating: 38
Blower-door test results: 0.6 ach @ 50 Pa
PHPP specific space heat remand: 3.16 kBTU / (ft2•yr)
PHPP estimated site energy use: 5,483 kWh/year (457 kWh/month)
Actual energy use (Mar. - Nov. 2012): 442 kWh/month
Space heating and cooling: Mitsibishi Mr. Slim 9,000 BTU/h ductless minisplit heat pump (MSZFE09NA / MUZFE09NA), supplemented by a coil in the ventilation ductwork that circulates fluid through a buried ground loop
Ventilation: UltimateAir DX200 energy-recovery ventilator
Domestic Hot Water: Solar thermal system with tankless electric-resistance backup
Appliances: Energy Star rated appliances (where applicable), induction range
Lighting: Tube fluorescent and compact fluorescent
Water Efficiency
• Low-flow plumbing fixtures
• Toto 1.28 gpf toilets
Indoor Air Quality
• Low-VOC paints
• Solid bamboo and ceramic tile flooring
• Balanced ventilation system provides fresh air to living spaces and bedrooms
21 Comments
Project
Great looking Project! congratulations!
Kudos!
I agree. It’s nice to see a good looking Passivhaus project; maybe other PH Designers should take notes.
2 questions..
First, with the pergola over the South facing windows... How much sun does this end up blocking in the winter months, and how much shade does it actually provide in the summer.
2nd. With regards to the insulated rafts.. How much clear space does this and others (corson's) houses have between grade and siding. In this one, it looks like the garage was framed directly onto the slab, with no raised curb. I would think it would be possible to grade properly, although the small section between the garage doors strikes me as a spot that would be raised due to driveway access and would have next to no grade-siding/framing separation.
Thanks Ann
Good article. Makes me wish once again for the (relative) simplicity of building 'new.'
I suspect friends and neighbors will get a lot more interested in this sort of not-so-bling "green" when word starts to spread about his utility bills.
No mention of water-resource management -- was any special thought given to that in the plan?
Nice Article...Daniel Ernst
Daniel,
Your personal house is still my favorite Passivhaus
https://www.greenbuildingadvisor.com/homes/farmhouse-style-meets-passive-house
A few comments ..1- why is
A few comments ..
1- why is it that we are discussing about efficient energy use on a house that ( i assumed south facing front ?? ) features no sun-shades on a little less than half of its sun facing windows ???
The first floor "treillis" is a nice try, but i believe that no direct sunlight should be permit to enter house through any south windows during day period of summer time,
and shade angles should be calculated ( or adjustable ) so that most SHG is received during winter heating time when it is required but all cooling season sun must be blocked.
This is the base.. if nothing is done to control that then i think that one have miss the starting point.
Now i do not know much about Zone 4 ... but how hard is it to achieve passivhaus standard in zone 4a ?? from the quick yearly average temperatures chart i found online, it looks like a very moderate climate ??
How does this affect planning on insulation levels and required SHG ??
Lastly, i have nothing against "regular" house look ( which seems to differ by region )
but when getting involved in a project that is "focused" on energy efficiency,
one has to let the "standard" lego block set on side and start using the "techno blocks" a bit more.
I see many different projects here that have some so-so compromises because the standard house/home model was to be followed.
Anyhow, it is refreshing to learn that the owners of this particular project have been able to achieve with a much acceptable budget compared to many others ...
Just like the current hybrids and plug ins cars, prices have to come down if we want
the efforts to be accepted and on par with the clientele.
Regular folks who need to save a few $ on fuel, usually don't have the 35 000$ to pay for a nice hybrid, and then low sales don't help high prices and the wheel turns...
Answers
Thanks Daniel for a wonderful write up; we enjoyed spending the day with you. Also, thanks for everyone's comments thus far. Let me make a stab at answering your questions.
John O: The pergola includes removable privacy lattice that blocks out the a lot of sun on the first floor of the house during the summer. Once removed for the colder months, the pergola is wide open blocking little if any sunlight. Additionally, we installed solar screens that roll down on each of the east and south facing windows providing 95% solar gain blockage; they are rolled up in the close months.. All said these features do the trick.
The garage is separated from the house's structure, insulation, and foundation. In fact, the only element missing on the west side of the house inside the garage is the HardiPlank. The slab is raised for the house which includes an insulation barrier. Although it looks like the garage is an extension of the home, its simply an attachment.
JoeW N GA Zone 3A: Our water supply is a deep well. No water resource management was included with the build; however, we recently installed (2) 65 gallon rain barrels for gardening and we're considering installing an underground tank for storage/emergency. A portion of the water runoff for our lot is diverted to a pond.
Jin K: Please refer to the first answer for John O. Although the pergola only shades the first floor, we have roll down solar shades that block 95% on the solar gain from the sun on each window. They were rolled up for the photo shoot. And yes, the house is south facing where most of its windows are located.
Insulation planning may be a better question for the builder, but this house does work well in this climate. At peak cooling we average $50-60 per month and at peak heating we average $60-65 per month.
Agree to disagree on the building styles. In our area, we build to suit the initial owner and prospective buyers in the future. Contemporary design (techno blocks) isn't ideal in our market; however, it may be in yours.
As for cost, the bottom line is that it cost us the same amount to build his house as a traditional built 2200 sq ft home that we previously picked out with another builder. Our only loses were half a bath, a bigger closet and some extra sq footage in the master. The real upfront expense is building any house, not wether it's energy efficient or not. In our current economy, its very difficult for the average consumer to afford the up front cost of building new unless you purchased your new home on a mobile home lot. There are zero down options surfacing, but we opted to save from paying PMI and put 20% down.
Based on what others are paying monthly for electricity, we spent less avoiding that 2200 sq ft traditional home that was only 400 sq ft bigger than this Passivhaus.
Jason: wow looks like superb
Jason: wow looks like superb performance for the cost !!
What is the "code built" energy consumption for a similar house ?
The roller shades are inside i guess from the pictures ...
Don't forget that even though the material may reflect a large portion of the solar heat,
the air between the glass and the shade grabs some of the multiple reflected heat..
still better than nothing ( and pretty cheap too ! )
I would've still opted for deeper windows and some additional overhang or some kind of fixed extrusion on top of the windows to block the sun from 11 am to 2-3 pm during summer.
one of the pictures depecting a window says " innie" window but i can only see a 3-4 inches of exterior trim around the window?? isn't more of a middle positioned ? or maybe the image gives
a wrong size impression ... anyhow, did you find it complex to properly install the windows and the surrounding trim/flashing ??
nice touch on the removable pergola lattice ...adustable is always good
( when the owner comprehends and takes time to use it )
interior material over fiberglass batts
In image 5 there appears to be a clear sheetgood material installed on the inside of wall framing, over the fiberglass-insulated stud bays. What is the material and what is its function?
Thanks.
Response to Rachel Wagner
Rachel,
Look close -- you can see the brand name. It's MemBrain.
thanks, Martin
Thanks for the better eye, Martin. Was the MemBrain used as a vapor retarder? Why would it be used as opposed to relying on latex paint as a Class III vapor retarder, given the location and type of air barrier and the use of 7" EPS outside the air barrier? I ask mainly because a big feature of this article was cost effectiveness, and I'm wondering why MemBrain was selected?
answers
I am the designer and builder of the home.
JK - the screens are on the outside of the windows. The windows are tilt and turn so they open to the inside.
Also cost premium was less than 20K, more than paid for the extra in the monthly mortgage by the onthly energy savings.
RW - We have used membrain because of ability to allow diffusion should there be vapor accumulation in the cavity. We have done this on all our PH projects to date, but now that we are getting data on the hygrothermal performance of these projects (7 so far), we find that the RH is staying pegged between 40%-60%, so we are rethinking the necessity and the cost.
Screens
Adam, Do you mind me asking what screens you spec'd on this house. I just noticed on the exploded view the slide bulge on the top of all the windows.. I'm assuming this is the screen rollup. Haven't seen many good options for exterior roller/blinds over in NA yet, other than in commercial use.
More on the Screens
Thanks again for everyone's comments, more pictures and video are also available on our blog at http://passivepreservation.blogspot.com
Jin K. / John O.: As Adam mentioned, the screens are mounted to the windows exterior thus blocking the solar rays before they enter the house. These screens are manufactured by Phantom Screens; believe it or not, they are marketed at Lowes - more info online. Our builder spec'd a rigid removable screen for the house, but we opted for the flexibility of a screen that could be easily raised or lowered on demand without a ladder. The Phantom Screens are costly but allow us more options on cool sunny fall and spring days. Adam can comment more on the spec'd screens. We are very satisfied with the Phantom Screens but the more dense the screen is the more likely they are to blowout in high winds; easily reset by retracting and then lowering, they've never lifted from the bottom latch even after this past summer's Derecho (70mph winds).
EPS foundation forms
Were the forms for the slab edge customized for this project? Are the angle, base and turned up edge one piece or is the edge a separate piece? Is the whole edge assembly 6" thick? Was exterior bracing needed for the forms? If so, what did you use for bracing? Did you eliminate bearing at the interior all together?
There are many things to like about this house. It is simple, small, well planned and executed!
EPS foundation forms -- another interested party
Would love to know where you got them.
EPS Forms
Kim and Ray,
We developed those forms as a product for sale. They are thermal bridge free, termite treated and can be used wherever your typical soil bearing pressure is under 3000# PSF and you are building lightweight frame buildings. They also require minimal bracing and come in 8' standard lengths.
If you would like to find more information feel free to contact me @: [email protected]
Is it really cool enough for, say, summer sleeping?
Jason, or someone else who may know:
I really like this house and its really good numbers.. It's been a while with no discussion about this place, but I decided to try to get answers to a few questions. I expect that the heating performance has been just fine, but I wonder about the cooling:
Has the single 9kBtu/h unit been getting the job done for cool sleeping during those hot, humid VA summer nights? (I live in MD).
Has the unit been adequate for keeping humidity levels comfortable throughout the house in summer?
Have you added any fans for the transfer grilles to help with bedroom cooling?
Answers
Has the single 9kBtu/h unit been getting the job done for cool sleeping during those hot, humid VA summer nights? (I live in MD).
The Unit is actually 12,000 BTU Mitsubishi and yes it keeps the house quite comfortable
Has the unit been adequate for keeping humidity levels comfortable throughout the house in summer?
Absolutely yes, it has stayed steady around 50% in the summers.
Have you added any fans for the transfer grilles to help with bedroom cooling?
When I designed the system we included Return Air Pathways in the design (http://www.tamtech.com/store/pressure-balancing-ashrae-energystar-hvac-air,category.asp)
They work well. In our Passivhaus projects, we use the point source units for cost effectiveness, if we can afford a ducted conditioning system we opt for that, but this system type can add 5-7k for a house like Jason and Stephs, so when we do not have the budget we use point source.
We install the RAPs and we advise clients that if a room is feeling hot, just open the door, and the comfort will return. This has proved true in all our point source projects.
Hope that helps.
Q: Was a rain screen ever
Q: Was a rain screen ever considered ?
Response to Chris M
Chris,
As the article notes, the HardiePanel fiber-cement siding was installed over Home Slicker.
Home Slicker is a three-dimensional plastic mesh product that creates a rainscreen gap between the back of the siding and the WRB. The mesh is deep enough to allow liquid water to drain and for a certain amount of ventilation drying.
Here is a link to a photo of Home Slicker mesh.
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