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Green Building News

Unity Homes Combines Prefab with Energy Efficiency

Bensonwood has launched a divison selling prefab homes designed to meet the Passivhaus airtightness standard of 0.6 ach50

Four designs, one airtightness standard. Unity Homes prefabricates the wall and roof components, which when assembled are designed to achieve minimum airtightness of 0.6 air changes per hour at 50 Pascals. Unity’s wall construction is designed to deliver thermal resistance of R-35, although clients can request a higher insulation level.
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Four designs, one airtightness standard. Unity Homes prefabricates the wall and roof components, which when assembled are designed to achieve minimum airtightness of 0.6 air changes per hour at 50 Pascals. Unity’s wall construction is designed to deliver thermal resistance of R-35, although clients can request a higher insulation level. Unity Homes’ Tradd 212, a traditional-style two-story home featuring two bedrooms, two and a half baths, and 2,056 sq. ft.
Image Credit: Unity Homes
The Tradd 212 main floor. The Tradd 212 second floor. Unity’s prefab construction specifications and onsite assembly techniques are designed to achieve airtightness of at least 0.6 ach @50Pa, one of the performance requirements for Passivhaus. The Zum 212, a two-bedroom, two-bath single-story house with a starting price of $298,500. The Zum 212 is 1,594 sq. ft.

Like many builders, Tedd Benson and his team at Bensonwood Homes have taken an active interest in the emerging market for energy-efficient homes. In addition to developing panelized construction techniques and producing many custom timber frame commercial and residential buildings since its founding in 1974, Bensonwood built a home in Norwich, Vermont, to the Passivhaus standard.

The Passivhaus project was instructive, Benson noted in a recent email to GreenBuildingAdvisor, not only because the building maximized energy performance as designed, but because it highlighted a performance feature – the Passivhaus standard for airtightness – that could be applied cost-effectively to other projects. The most visible of those “other projects” is Unity Homes, a separate homebuilding company that offers four basic designs, relies heavily on prefabrication, and builds its homes to meet or exceed the Passivhaus airtightness requirement: 0.6 air changes per hour at 50 Pascals pressure difference.

Passivhaus certification is optional

Benson, who is chief of Unity, makes a point of noting that while airtightness and energy efficiency are virtues of Unity’s houses, Passivhaus certification is not a requirement.

“Because of how our building systems work, and our off-site fabrication precision and control, we decided to make the (Passivhaus) airtightness requirement the Unity Homes standard,” Benson explained. “But we did not decide that all of our homes will be PH!”

Other minimum performance standards for Unity include wall insulation to R-35 and roof insulation to R-44.

Four basic styles, one airtightness standard

By the time Benson announced the company’s launch, in an October 9 post on this blog site, “The New House Rules,” the company’s first two homes were already in production.

The Unity lineup includes a two-story traditional style home, the Tradd, offered in configurations ranging from two to four bedrooms; a single-story cottage, Xyla, in configurations ranging from one to three bedrooms; a two-story Swedish-inspired home, Värm, available with two to four bedrooms; and the modern-style Zum, a single-story with two to four bedrooms.

Prices cited on the Unity Homes website exclude land, permits, site improvements, taxes, and shipping and onsite assembly charges for locations more than 50 miles from the company factory, in Walpole, New Hampshire. Unity has tried to keep prices relatively affordable. A 2,056-sq.-ft. configuration called Tradd 212, with two bedrooms and two and a half baths, for example, starts at $339,500.

The Zum line, meanwhile, is designed for maximum passive solar benefit and tends to be a little more costly per square foot. It starts at $298,500 for a 1,594-sq.-ft. two-bedroom, two-bath called the Zum 212. And though slightly smaller than the Tradd 212, the Zum 233 – a 1,773-sq.-ft. three-bedroom, two-bath – starts at $373,250.

For now, at least, distribution is geographically limited

Benson says that while most of the company’s focus is on the Northeast, the plan is to expand production to other parts of the country with the help of additional partners and investors. And with expansion should come economies of scale, Benson adds, that will help drive down costs. Still, the current prices offer good value, he says.

“We know we’re starting out well enough in pricing that these homes will be competitive with very inferior conventional alternatives in many markets.”


  1. bthervey | | #1

    KevinD: Clarification, agreement, disagreement, promise
    CLARIFICATION: The homes in the Unity series vary in price.The $185 psf you reference is not standard in Unity pricing. We also have models in the Värm family that are quite a bit less, falling in the $160 psf range. In addition, we have quoted prices that are even less than that, with adjustments to the finish and fixture specifications. Also, I’d like to point out that our prices do include foundations. We leave the sitework out because it’s a number we can’t possibly know in advance.

    AGREEMENT: Unity Home prices are higher than we wish or intend in the long run. The affordability we aspire to achieve is a path, not a destination, and we’re solidly on that path, and already moving fast. I also agree about the inherent Catch-22 in cost and production, but it’s not a trap we’re unable to escape. Our technology and construction methods uniquely position us to wiggle our way out, and we will.

    DISAGREEMENT: We chose the very highest building standards for Unity Homes. Not only are there no compromises, but we are committed to raising the standards of building quality and energy performance to the highest practical level:

    My disagreement is that even our current pricing is extremely good for this building quality. Had we lowered the standards, the prices could have been much lower. Also, I need to point out that in many markets, the Unity Home pricing is already competitive with the local standard construction alternatives. Where building costs are higher, Unity Homes can compete in cost with lower quality alternatives right now. That’s only one of the reasons the Unity launch has been successful.

    Here’s why homebuyers have been attracted the Unity Homes propostion:

    250-500 year homes, with mini-energy requirements
    PH airtightness (0.6 ach50)
    triple glaze windows and doors.
    Very high insulation levels, optimized where returns fall off and small air source heat pump systems can efficiently heat and cool.
    No fossil fuels; zero net energy capable (4-8 kW PV array). The option of no heating, cooling, electricity costs...forever. That's worth a lot.
    “great home” specifications
    toughest structural standards: “bunkers for the storms.”
    Open-Built systems for disentanglement for short and long-term building adaptation for upgrade, change and inhabitant change.
    Legendary Bensonwood craftsmanship on fit and finish is standard.

    In a Treehugger article about Unity Homes, Lloyd Alter summed up our quality standard:
    “..these houses have killer specifications for such a price: R-35 walls, R-44 roofs, triple paned Loewen windows, tightness to passivhaus standards. Materials are all healthy choices, with low or no VOC finishes, cellulose insulation, and lots of natural light. The base finishes are any other builder's upgrades, with no vinyl to be found.”

    We think more homes should be built this way, and therefore it’s these high standards that we decided to commit to.

    PROMISE: As we wiggle our way out of the Catch-22 trap, the cost of Unity Homes will go down and our standards will not.

  2. kevin_in_denver | | #2

    Sorry, Still too Expensive
    At $185/sq. ft. , this building model has a looong way to go to capture any market share.

    Don't forget you have to add another $10-$40/sq.ft. for foundation and site work.

    It's the same catch-22 that has always plagued this industry. You can't get cost down without getting volume up, you can't get volume up without getting cost down.

    The only successful modular manufacturers so far provide unappealing crap for $45-$85/sq.ft., and nobody has been able make the transition. Even Warren Buffet's Clayton Homes has stopped making the i-House. It was on the right track, but customers stayed away in droves. They may have tried harder if not for the Great Recession.

  3. Robert Swinburne | | #3

    Good on Benson
    These are good prices for this area.
    I appreciate the no compromise notion. This is the standard to which we will all be building sooner than later so why not be a decade ahead of the curve? Everyone else will be playing catch up including the $85/s.f. modular home manufactures.
    Benson is just listening to the winds of change and sowing the seeds of success.

  4. DC_Eakin | | #4

    Appreciate the effort; doubt the efficacy
    I also applaud the Benson effort - it should be (relatively) easy to engineer-in excellent, repeatable building techniques in a controlled factory environment. But as has already been observed, the cost-per-square-foot does not yet reflect any major reduction that mass-produced modularization should bring (especially the Zum line as all forward-thinking builders should be concentrating on passive solar integration).

    And what's with the R-35 walls and only R-44 roofs? Even if you take the current ratio "code-built" homes use (R-19 walls, R-38 ceilings) the Benton ceiling results should be R-70. I've not yet looked closely at the plans but I would hope they are using raised-heel truss roofing systems to allow 24" or more ceiling insulation across the entire ceiling plane. If not, this is a design no-starter and does little to align with the other Passive House design parameters.

  5. bthervey | | #5

    Response to David E.
    Our mantra in the development of Unity Homes is: "Neither compromise nor maximize, only optimize." We therefore did not fall in lockstep with the prevailing easy formulas about insulation levels because at a certain point the added costs give too little return on the material/labor investment. As we seek out the best optimizing levels, the goal is "low load," not Passive House. We are trying to achieve peak loads between 12K to 25K BTU per hour in the cold climate zones. At this low-load level, minisplit heat pumps are effective, and therefore zero net energy with relatively small PV arrays are possible.

    In the pursuit of the most optimized approach, here are a couple of things we have proven (at least to ourselves and our clients) in 35 years of building energy efficient buildings:

    1. Air tightness trumps R-Value for value. Added R-Value is more insulation and more cost. Air-tightness is mostly just good practice and is nearly free. So we're maximizing what's free so we can optimize the stuff that brings higher cost. A building with our slightly-lower-than-Passive House insulation levels with the PH airtightness of 0.6 ach50 is the more cost effective way to achieve our low load goals..

    2.In airtight, well insulated buildings the so called stack effect barely exists, if at all. Therefore, there's little justification for a big differential between the wall and roof insulation levels.

    We were one of the lone pioneers of SIPs, as we started using them on our timber frame buildings in the late '70's. Since the technology was yet unproven in residential construction, and the SIPs industry wasn't born yet, that was risky, but the performance was extraordinary for the time. By wrapping the frame in a SIPs blanket, our air-tightness and reduction in thermal bridging immediately set a new standard, and the usual 4 to 6 inches of urethane foam we used in the 70's and 80's was extremely effective compared to conventional alternatives. We don't use SIPs as much anymore (only over timber rafter roofs), but we also have brought the good lessons from our SIPs era forward to Unity Homes, and using relatively equal levels of insulation is one of them. I'm sitting now in my 1979 built home. It's not insulated or air-sealed to the Unity Home standard, but still the temperature on the first floor is constantly within a degree or two of the temperature 22 feet up in an open area in the front section. Because of the SIPs and the air tightness, I don't have convective heat loss; it's all conductive loss through 4 to 6 inches of foam...essentially molecule to molecule, and they don't know up from down. Since the temperature doesn't vary much, I'm losing heat more or less equally through the walls and through the roof.

    We are building a lot of homes (Unity and Bensonwood) to this optimized standard: R35 wall; R44 roof; .06 ach50.; triple glaze windows. It's a good formula for a great level of performance that allows us to eliminate fossil fuels and create zero net energy ready buildings in even the toughest climate conditions.

    Pay attention to Unity Homes. There's one coming to your neighborhood. The quality and performance WILL be high; the cost WILL come down.

  6. TKelton | | #6

    I'd buy one!!
    To begin I would like to ask David and Kevin if they are familiar with the current prices of triple glazed windows? If not, please research, recalculate and then see if you believe the SF cost is still too high. For the whole package the pricing seems just about right, and when you add in the quick site times they are claiming, it seems like a steal.
    As someone who focuses on energy for a living, and after seeing the pictures and videos of how fast these homes are going up I would build one in a heart beat, if I had not spent the past few years and thousands of dollars making my own home in Maine more efficient.

    I can say in terms of the additional insulation in the roof that David questioned that once any home has achieved a certain level of insulation, the monetary expense of additional insulation makes less and less sense. And with a super tight home the ratio of insulation from walls to roof means practically nothing. The idea of the stack effect should only be applied in terms of convection not conduction.
    I applaud Mr. Benson and his company for striving to make those levels of efficiency affordable in home building. As the energy codes become more strict there is going to be a lot of struggles in the industry keep up, it is inspiring to know that there are companies out there that are already achieving them at an affordable rate. Way to go!

  7. DC_Eakin | | #7

    In response...
    Ted - I agree that air-tightness trumps R-value for COMFORT (not for value as it is much cheaper to add insulation - even at new construction - than labor efforts to ensure air-tightness) and also agree that good air-tightness does come down to attention to detail and good, consistent building practices. I somewhat disagree that improved air tightness greatly reduces/eliminates the stack effect. If a room air volume is not acted on by other means, the stack effect will be created as air is warmed and rises to the upper-most level of the living space. However, most buildings with high levels of air-tightness also employ some form of mechanical air exchange to improve IAQ - which has the side benefit of de-stratifying (a term going back to the '70s) the interior air, creating the consistent temperatures observed regardless of interior height. Bottom line - no mechanical air movement = stack effect.
    You do make an interesting thesis about the relationship of insulation levels and the delta T - if the interior air is the same temperature regardless of location and the air temperatures on the other side of the room plane (attic if there is one; outside air if not) is the same temperature, then the delta T will be uniform on all interior planes so there should not be a need for additional insulation on the upper plane as there is no difference in delta T. If this thesis is proven (probably a lot of debate regarding attic spaces' temps versus ambient air temps), it could lead to a shift in building costs from super-insulated ceilings to better interior air management systems as it would work better.

    I am looking forward to Bensonwood Homes moving into the mid-Atlantic region.

    Tim - RE the monetary expense of additional insulation (or any performance enhancements done to the shell) - the ROI of these costs need to be calculated for the expected lifetime of the shell (like 100 years) not just today's utility costs. That is the same flawed logic builders 20-30 years ago used and is why there are so many existing homes with (now) inadequate insulation levels. Given that insulation is one of the least expensive elements of building construction, adding considerably to the R value really does not add appreciably to the overall costs and is a negledgeable cost over the lifetime, but will greatly add in reduced utility costs and comfort levels in the future.

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