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A Kit House for the 21st Century

A Maine company has developed a prototype building insulated with curved structural foam panels

Six-inch-thick curved structural insulated panels are an integral part of the design of the “Ultra High Performance Building Shell System” developed by a Maine entrepreneur.
Image Credit: All photos: Shelter+7
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Six-inch-thick curved structural insulated panels are an integral part of the design of the “Ultra High Performance Building Shell System” developed by a Maine entrepreneur.
Image Credit: All photos: Shelter+7
“Shoes” attached to the concrete foundation anchor the ends of the curved glue-laminated beams that make up the frame of the building. The glulams making up the frame are fabricated with scraps of softwood that would otherwise be sent to a chipper. The company can source them from producers in either New York or Quebec. Once panels have been attached to the frame, the seams are sealed by injecting foam into raceways, forming what the company says is an unbroken layer of exterior insulation. In larger buildings, a second floor can be added with floor joists attached to steel hangers. The shell, however, is self-supporting and has no interior load-bearing walls. The finished exterior of the first prototype building in West Gardiner, Maine.

UPDATED on Jan. 18, 2016

A Maine-based company has developed a prototype house made from arch-shaped glue-laminated beams and structural insulated panels (SIPs). The company promises speedy construction, a high level of energy efficiency, and low long-term ownership costs.

It looks just like a Quonset hut of World War II vintage, but Thom Labrie calls his “Ultra-High Performance Building Shell System” a 21st-century innovation that makes more sense than a conventionally framed and insulated building.

The buildings have only three components: the frames, the panels, and the steel “shoes” that connect the frame to a concrete foundation. The curved panels are manufactured with an OSB face supplied by Huber, maker of the Zip sheathing system, and include 5 1/8 inches of closed-cell polyurethane foam. When the panels are applied to the frame, they create an uninterrupted layer of insulation. Plumbing, wiring and other utilities are run inside.

“The building industry has been stuck in a box for so long,” Labrie said by telephone. “We’re in the 21st century. When you consider the technology, the materials, the know-how we have today, continuing to build these boxy structures, these balloon-framed structures that were developed in the 1800s, it doesn’t make any sense. There’s a better way to do it.”

Labrie’s company, called Shelter+7, has a distributor in West Gardiner, Maine, Archtype Structures, and has built a prototype building that is used to make the curved SIPs, but it has yet to sell a single structure. The company’s first sale, Labrie hopes, will take place this year.

Three sizes, but any length you want

The company offers buildings in three sizes, measured in the number of 4-by-8-foot panels it takes to make the arch. A 13-panel “bungalow,” for example, uses 13 panels to go from the foundation on one side of the building to the foundation on the other side, a distance of 52 feet, on a foundation 40 feet wide. The bungalow is essentially a one-story building.

A 15-panel structure, with an exterior covered by 15 panels, can accommodate a loft, and a 17-panel building has a full second floor. All of them are built with the same 40-foot width. Buyers can order buildings in whatever length they like, in 4-foot increments.

Labrie says that packages are available in one of three levels of completion. At the low end, a buyer can order just the building shell that’s erected and closed in by a company-trained crew. The other options are a shell with some of the exterior and interior finishing done, or a “full turnkey” building that’s completely finished.

Prices for fully completed buildings range from $90 to $132 per square foot, depending on size. Labrie said that the largest building, a 40-foot-long 17-panel structure with a full second floor, three bedrooms, 2 1/2 bathrooms, and an office/guest room would have 3,042 square feet of usable interior space and cost $273,366 — about $90 a square foot. With similar fixed costs and less interior room, the square-foot cost of the smaller buildings are higher.

Arch construction is key

The curved glulams are an essential feature of the design, not only because the frames can go up quickly but because they are structurally robust. Just as important, they’re made from short lengths of softwood that would otherwise go to the chipper, Labrie says.

“We grind up billions of board feet of wood in this country that is very usable,” he said. “Part of this building concept is to utilize some of that material and not put it into chippers.”

Shelter+ can source the curved beams from sources in either New York or Quebec, with a lead time of between 6 and 8 weeks.

Labrie says that his background is in the design and manufacture of machinery used to make products from waste wood. When he began designing his own house, an underground structure where he’s been living for 35 years, he leaned toward incorporating arch-shaped components.

“I started with an arch because it is the absolute most efficient way to cover square footage,” he said. “You use less materials to get the job done.”

Intrigued with the design possibilities for arches, Labrie approached a culvert company in the mid-1970s in hopes of interesting them in a collaboration to build houses. They didn’t nibble, and Labrie shelved the idea. Years later, the idea bubbled back to the surface.

Arches also create a free-standing structure that doesn’t need any load-bearing walls inside. As a result, moving partitions and changing a floor plan is both simpler and cheaper than it would be in a conventionally framed house.

“With the structure totally free-standing, lofts and second floors can be constructed only when desired or needed since they do not play a structural role in the building shell system,” the company’s web site says.

Designed to meet latest energy code

Insulated panels come in only one thickness, with an R-value of about 33, and Labrie said he has no plans to offer a thicker panel. This looks as if it might pose a sort of code conundrum for the company. R-33 is far below the prescriptive insulation levels required in ceilings by the International Energy Conservation Code in all but Climate Zone 1. But it’s better than what’s required in wall insulation in all climate zones.

In a house with a semi-circular cross-section, what’s a “wall” and what’s a “ceiling”?

According to the web site, the building system meets or exceeds requirements of the 2015 IECC and scores 45% to 55% better than the current HERS standard reference design, and is 25% better than Energy Star models.

Steve Carr, the project’s energy consultant and the HERS rater for the project, said the buildings are able to meet energy codes through either a performance path or by its Energy Rating Index, rather than the code’s prescriptive path. “Instead of looking at the R-values or the U-values specifically, it looks at the whole performance,” he said.

At a minimum, the shell of the building scores 60 on the HERS index, and can score lower depending on what mechanical systems are used, Carr said.

Do curved roofs last longer?

The web site also claims that the curved surface of the buildings are better at deflecting damaging UV radiation, and that the curved shape should make roofing last longer.

“In addition,” the web site reads, “the curved geometry of the structure can significantly reduce the wear and tear on roofing material. Flat areas of roofs are exposed to considerably longer periods of damaging reflective UV rays from the sun which naturally causes heat build-up, excessive transfer of energy through the roof structure, premature material deterioration and higher energy and maintenance costs.”

It continues: “Dome building, elliptical building, curved and gothic roof surfaces naturally deflect the majority of these damaging rays, reduce potential heat build-up and energy transfer, and in turn, facilitate longer service life of the roofing system along with lower energy and maintenance costs.”

On this point, Labrie said he had no study data to confirm the statements, but said he had been told by two roofing company technicians it was a “reasonable assumption.”

“My common sense says to me if you have all these rays coming down, if they’re hitting a flat surface from whatever angle the sun is at, you’re hitting a much larger area at a given moment vs. a curved surface where that direct hit is over a much smaller area,” he said.

A big market for this kind of building

Despite an early marketing misstep, Labrie sees wide-open opportunities ahead.

Buildings can be put to a variety of residential and commercial uses, and may find a special niche in the “after the disaster market,” Labrie said, because the structures go up so quickly and provide effective protection from the elements. With the foundation in place, a building can be closed to the weather in less than a week.

He also hopes the concept will appeal to younger buyers who are looking for something a little different.

“Once we nail one or two of those down, I think we’re good to go, because the performance of the building is extraordinary,” he said.

“The millennial generation is coming up. They don’t want their father’s Buick. That’s not what they’re after. That generation wants something that’s different, that’s modern, that’s techy, and that’s green.”

This post was updated to reflect changes at the company’s website about about the efficiency of closed-cell polyurethane foam.


  1. JC72 | | #1

    The ZIP-SIP!
    As a ZIP System fanboy I couldn't help but wonder what sort of stress the curvature the roof would have upon the WRB properties of the ZIP sheathing.

    From a layman's perspective I would think that due to the curvature SIPS made with thin plywood would've been better suited.

  2. RedDenver | | #2

    Metal fab
    Haven't buildings like these been around for decades? They're just made from a metal skin which could be insulated on the interior.

  3. lymanterrell | | #3

    Lstiburek Vapor Ridge Vents
    Would a ridge vent with a Vapor permeable membrane be in order on a structure like this?
    I seem to remember Lstiburek talking about SIPs failing in roofing assemblies because the moisture would enter the SIP from the interior (because the joints are hard to tape completely on the inside) and then stay in the SIPs because the outside of the SIP are properly sealed.

  4. Expert Member
    Dana Dorsett | | #4

    5 1/8 inches of closed cell polyurethane (sigh...)
    That's at best R35 whole-wall, after surface finishes, not even up to "pretty good house" levels, especially given that it's the same up-top as it is on the sides. OK a HERS of 60- it beats code min, so what?

    “The millennial generation is coming up. They don’t want their father’s Buick. That’s not what they’re after. That generation wants something that’s different, that’s modern, that’s techy, and that’s green.”

    I'm not sure how different, modern or techy this really is compared to your great grandpa's quonset hut but maybe they can convince some people that it's all of the above. I'm a complete skeptic that it's very green at all, given the choice of materials.

    The HFC245fa blowing agent becomes a serious issue a high-R, with a 100 year global warming potential ~1000x that of CO2. How green is that, really?

    An 8.5-9" arched OSB monocoque of half pound foam would deliver comparable or better performance with the closed cell foam, and being blown with water, at tiny fraction of the climate damage. Even with the less-rigid fill it would be stronger than flat SIPs with 1.5lb EPS cores due to the inherent rigidity of the curved OSB skins. A curved EPS sip of 7.5-8" would have comparable thermal performance and stiffer than an open cell polyurethane SIP, with less than 1% of the climate damage. Blown with pentane (~7x CO2) it would potentially have VERY low climate damage if the pentane blowing agent is recovered and burned at the manufacturing site for process heat, as is commonly done by some EPS molders.

    Going Net Zero Energy with that type of shell design cold be tough, trying to figure out how to hang the PV.

    Just as with dome homes and arch homes of the past, lack of usable wall area and hanging cabinets etc in the living spaces can become interior design challenges.

    David Peterson's question is also of real concern, given the number and locations of seams that have to be sealed.

  5. GBA Editor
    Martin Holladay | | #5

    Response to David Peterson
    The solution to the problem you are talking about is to tape the SIP seams on the interior. For more information on this issue, see Air sealing SIP seams.

  6. lymanterrell | | #6

    SIP Seams Over Beams
    The SIP Seams seem to be placed directly over the beams in this construction (going vertically), which wouldn't lead themselves to taping very well. Perhaps the interior air conditioning would be solve the problem by drying the SIP arch to the interior of the building.

    Edit: A more specific question is, does this particular company know that they need to tape underside of their SIP panels during installation to prevent moisture issues?

  7. GBA Editor
    Martin Holladay | | #7

    Response to David Peterson
    The colder the climate, the riskier it is to try to build a SIP building without interior tape. Cold-climate builders have learned to drape wide pieces of tape over the beams before installing the SIPs. It's awkward, but it's necessary to keep the builder out of trouble.

    I have no idea whether the owners of Shelter+7 or Archtype Structures understand the need for interior tape in cold climates.

  8. Expert Member
    Dana Dorsett | | #8

    On the other hand...
    At 5" the closed cell polyurethane itself is structural, and should the exterior OSB rot away it wouldn't change the structural integrity of the building by very much, unlike EPS core SIPs.

    I'm sure there will be a learning curve to assembling these in a way that will stand the test of time. If they fail in only 50 years it's unlikely that the environmental hit from the foam will ever be recovered in lower energy use.

  9. Peter_Rogers | | #9

    "Learning curve." Har Har.
    "Learning curve." Har Har.

    Goddamn, that is one ugly house. Who selected that cladding?? They'd better get a good designer involved if they want to sell this thing.

    Thought experiment: can anyone envision a way to build an arched structure like this using a truss and blown cellulose? Ever since I audited a hippie built geodesic dome style house I've had this silly dream of a double-walled geodesic dome-like structure (zero thermal bridging!) but looking at this makes me think an arch would be simpler.

  10. charlie_sullivan | | #10

    Thought experiment

    I tried your thought experiment. Running the experiment in my limited-capacity brain, I found that:
    1) The construction was feasible, and it achieved a high R-value with vastly lower global warming impact than the idea presented here.
    2) It required a vent space between the cellulose and the outer roofing/cladding, just like a cellulose insulated cathedral ceiling, only it was harder to figure out how to install the ridge vent.
    3) It was still ugly.

  11. dsmcn | | #11

    So: innie or outie windows?
    The arched exterior puts a new slant on both options (sorry).

    Having seen stone arches in the Middle East and India that are still standing without even mortar, arches do have the attraction of a durable structural design. Still, my wife would not consider such an expanse without a window. No ERV could vent the sense of oppression/depression that would result from living in a seeming cavern.

    Might make a great shop though.

  12. user-714815 | | #12

    Thought Experiment
    To address the "ugly", let's have two arches intersect, like a +. Then you have four vertical faces, more light, and a beautiful interior ceiling structure.

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