Tuesday April 30, 2013

Last week, I provided a little background on Tedd Benson and his evolution that led him to found Unity Homes. This week, I’ll describe some of the features that set Unity Homes apart from both standard home construction and other panelized and manufactured home production.

An emphasis on
energy performance

A top priority for Unity Homes is energy performance. The homes have R-35 walls and roofs that vary from R-38 to R-48 -- depending on the roof spans. (Longer spans require deeper rafters (made from engineered I-joists) with room for more insulation.)

Unity’s R-35 wall does better than some R-35 walls, because thermal bridging through the framing is minimized. The wall system uses 9.5-inch-deep I-studs, so there isn’t a lot of higher-conductivity wood.

Unity uses triple-glazed, low-e, argon-filled Loewen windows throughout to control heat loss. With every house, designers consider window orientation and area and usually specify different glazings for different walls--installing windows with a higher solar heat gain coefficient (SHGC) on the south side. I was surprised that the highest SHGC for Loewen triple-glazed, low-e windows is 0.44, while some other manufacturers offer triple-glazed, low-e windows with SHGC ratings up to 0.60.

Like me, the folks at Unity Homes (and Bensonwood) are frustrated with what’s available in the way of energy-efficient doors.


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They have made a lot of headway by pre-building entire entry modules in the factory (with pre-hung doors and all the air sealing needed in the surround), but the doors themselves continue to be a weak point. Tedd let me know that indeed his team has been working on developing a better insulated door, and they expect to have prototype soon. I’ll keep an eye on that.

The other major energy feature of Unity homes -- perhaps the most important -- is air tightness. Through a combination of precise cutting of framing members, use of Huber Zip sheathing with taped joints, and advanced European gaskets, Unity Homes achieve the very stringent Passive House standard for air tightness: 0.6 air changes per hour at 50 pascals of pressure difference across the envelope (ACH50). A recently completed Unity Home in Brattleboro (the company’s first) came in at an impressive 0.51 ACH50 in testing by Efficiency Vermont.

Tedd argues -- correctly, I believe -- that with very tight construction it’s not as important to have a lot more insulation at the roof than in the walls, because there won’t be as much thermal stratification as in conventional houses. In fact, the homes do so well, that single point-source heating systems, such as air-source heat pumps, usually suffice as heating systems--at least for smaller homes.

Scoring energy performance

The Home Energy Rating System (HERS) is a standardized metric for reporting the energy efficiency of houses. In the HERS rating system, a score of 100 is a standard new home built to code. A score of zero would be a net-zero-energy home (one that uses no net energy on an annual basis, beyond what is produced by the house -- typically using a rooftop solar-electric system). An average existing home being sold today has a HERS rating of 130.

A standard Unity Home should achieve a HERS score of about 40, while the Brattleboro house had a HERS score of 44 (three points were lost because the insulation couldn’t be inspected). Thus, Unity Homes should use only about 40 percent of the energy of a new home built to code. This energy consumption is low enough that with energy-efficient appliances and lighting and an energy-efficient air-source heat pump, a roof full of solar panels can bring the HERS rating down to zero.

It’s not only about energy

Performance is also about durability, and Unity Homes’ meticulous attention to building science and quality control during production should ensure far greater durability than standard homes. In fact, Tedd talks about a 250- to 500-year life for his homes. (With the home my wife and I are building in Dummerston, our goal is a 300-year design life, but such longevity goals are almost unheard of today.)

I’ve visited Tedd’s Walpole, N.H., factory twice now, and continue to be impressed with his use of state-of-the art materials and technology from around the world -- especially Sweden, Switzerland, Austria, and Germany. I’ve seen materials in standard use by Unity Homes that I’ve never seen before--like dual-bead gasketing that fits into precisely cut eighth-inch spaces between framing members.

Green materials

The life-cycle assessment of materials has also guided decisions with Unity Homes. For example, the company has largely eliminated the use of foam-plastic insulation, due in part of concerns about flame retardants and the high global warming potential of certain products. Instead, cellulose insulation -- made from recycled newspaper with borate flame retardants -- is used in the walls and roof.

The foam that is used on the foundation walls is extruded polystyrene salvaged from commercial or industrial projects. And timber elements used in the houses -- there are a few to serve specific load requirements and add aesthetic appeal -- are typically glulam beams, but substitutes are possible, including salvaged timber from old buildings.

Vinyl (PVC) has been largely avoided in Unity Homes, except for wiring and drainage piping. Siding is typically cedar shingles. And zero- or low-VOC materials are used throughout.

All right, some of those air-sealing materials coming from Europe take a lot of energy to ship here, but Tedd told me that there is interest from the supplier to set up U.S. production here if demand increases sufficiently.

Affordability

Driving down cost, as noted last week, is a driving priority for Tedd and Unity Homes. The price of new, high-quality, custom homes today is often around $200/square foot, according to the company, while the first Unity Homes are coming in at around $160-$170/sf, including foundation. The company’s long-term goal is to bring that cost down to $130/sf., which would be slightly less than the average cost of a resale home ($140/sf).

In addition to the actual cost, another concern with home building is the variation from budgeted cost. A typical custom home often exceeds budget by as much as 35 percent, while the first Unity Homes have come in just 5 percent over budget. The company’s goal, not surprisingly, is to come in right on budget.

Speed of construction

Finally, Unity Homes go up fast. The on-site assembly of the weathertight shell is usually accomplished in one to three days, depending on complexity and garage options. From there, Unity Homes are finished quickly because of the open layout and packaging of systems, such as pre-assembled HVAC modules--strategies that had their origin in the Open-Built system described last week. While a standard new homes takes 150 days to build (and some take a lot longer--ask me about that sometime), Unity Homes can get the build cycle down to 35 working days currently, and the ultimate goal is 20 days.

Continuous improvement

Tedd is pretty clear about his aims with Unity Homes. "We think building a house should be fun, and more people should be willing to engage in the building of their own home," he told me. "Unfortunately, people tend to be deathly afraid of it because it takes so long and is traditionally such a complex and stressful process." He reminded me of the oft-heard expression, ‘build a house, lose a spouse.’ "What if it only took 30 working days, all costs were known, the build quality was above anything experienced, and it could have a net-zero-energy impact forever?"

Unity Homes may not quite be there yet, but I believe they are further down that path than anyone else in home building today. To learn more about this unique company, which (with parent company Bensonwood) employs 80 people in Walpole, visit www.unityhomes.com.

Alex Wilson is the founder of BuildingGreen, Inc. and the Resilient Design Institute (www.resilientdesign.org), both based in Brattleboro. Send comments or suggestions for future columns to alex@buildinggreen.com.