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10 lessons learned from building a zero-energy home
Developers of a cost-conscious zero-energy home offer guidance on building uber-green homes on a budget.
Developers of a cost-conscious zero-energy home offer guidance on building uber-green homes on a budget.
Photo: The 2,700-square-foot Energy Efficiency Lab Home near Pittsburgh was designed and built with the goal of making net-zero-energy homes affordable for production builders and buyers alike. Features include staggered-stud wall framing, enhanced insulation systems, and use of off-the-shelf products.
In November 2010, the Best Practices Research Alliance cut the ribbon on its Energy Efficiency Lab Home outside Pittsburgh. A collaborative research-based community focused on improving the quality and performance of homes, the Alliance was founded by IBACOS, a building science consulting firm and team leader for the Department of Energy’s Building America program.
The lab home is part of an ongoing effort by IBACOS and its Alliance to test methods and materials that will make net-zero-energy homes affordable for production home builders to build and the average home buyer to purchase.
The 2,700-square-foot lab home, which will stay unoccupied for three years while testing continues, features a super-insulated enclosure, a ground-source heat pump system, three different HVAC distribution systems, a high-efficiency lighting system, and solar panels. The lab home project team, which was headed by me and central Pennsylvania home builder S&A Homes, found out first-hand about the obstacles likely to crop up during the construction of a zero-energy home like the lab home.
What follows are 10 lessons learned from the project. For more on the lab home, visit: www.theresearchalliance.org/lab-home.aspx.
1. Design with production in mind
For high-performance homes to be widely available, production builders have to be able to build them at a reasonable price. “Our goal as a builder is to maximize energy efficiency without creating price barriers for future homeowners,” says Chris Schoonmaker, VP of S&A Homes. That’s why the lab home was designed with off-the-shelf products and processes that production builders either already know of and use or could adopt and modify to fit within their existing infrastructure.
Reed Kneale, VP of operations with O.C. Cluss Lumber and Building Supplies, which produced and assembled the lab home framing, says one key to gaining his employees’ acceptance for some of the new methods and materials used was sticking to production-minded processes. “I can attest it was real-world techniques, on steroids,” he said.
2. Think outside the box when it comes to materials
In order to achieve high-performance homes, designers and builders may find themselves using commercially available materials in new ways. For instance, rather than relying solely on interior air sealing or the use of spray foam insulation to provide the air-tightness strategy, the lab home uses well-detailed and integrated housewrap on the exterior to reach the extreme air-tightness targets of the project. In addition, the home features 2 inches of foam sheathing on the exterior that would normally be used for interior basement walls.
The sheathing’s pre-rabbetted channels along the vertical edges, which incorporate the use of furring strips for fastening, allowed the team to use common framing nails to attach the foam to the wall, rather than expensive long screws. The furring strips also provided a nail base for vinyl siding, saving money while netting the aesthetic requirements and thermal performance desired.
3. Staggered stud design pays off
Even though many standard-panel design software products don’t accommodate staggered-stud layouts, the team decided it was the best approach for the project. Designing the lab home’s above-grade wall system using 2x4-inch, staggered framing resulted in several clear advantages. Staggering the studs means fewer direct pathways for energy loss through the wall, and the smaller dimensional lumber is less expensive than larger dimensional studs, meaning lower costs for the builder and potentially the homebuyer.
The wall panelization and onsite framing contractors also found that the framing strategy was an easy alternative, requiring minimal training and few changes to their standard methods. As an added bonus, running electric services through the walls was easier and more efficient for the installer than their typical method of drilling through studs and top plates, since wiring could be woven through the stud bays.
4. Make sure your materials are readily available
Even with commercially available materials, sourcing for a high-performance home can be difficult, since those materials may not be lying around a local supply yard. It was determined that a 3-inch-thick polyiso board would work best for inside the formwork of the foundation walls, and the supplier confirmed it was available. However, when it came time for the foundation walls, the supplier said the board would first have to be manufactured, potentially resulting in a month’s delay.
After waiting two weeks, the project team opted for an alternate solution — using readily available 2-inch-think polyiso board and applying a separate layer of polyiso to the inside of the foundation wall after the forms were stripped. The change in thickness of foam inside the formwork (from 3 to 2 inches) meant ordering new break-back form ties, delaying the project by an additional week. All told, the material availability and sourcing issues, coupled with weather delays, increased the cycle time for the foundation by about one month.
5. Little improvements add up
The lab home aimed to evaluate how effective the use of a well-sealed and integrated exterior housewrap would be toward reaching an aggressive building-envelope leakage rate of 0.60 ACH50. IBACOS tested the house when the housewrap was sealed on the exterior and integrated with the foundation and attic air barriers before any other interior air sealing or insulation measures were initiated. To our surprise, the leakage rate was only 3.0 ACH50. Each additional air-sealing measure offered incremental improvements that made a significant difference.
With the application of spray foam to strategic areas in the attic (e.g., over top plates of interior-partition walls, wiring and plumbing penetrations, and recessed light fixtures), the leakage rate was 0.88 ACH50. With spray foam in the band joists, it was 0.77 ACH50, and when the wall cavity insulation and drywall were installed, it dropped to 0.65 ACH50. After all the trim, caulking, and painting were completed, the lab home scored 0.54 ACH50, surpassing our target.
There are different approaches that can be used in different combinations, for varying degrees of cost and effort, to achieve aggressive levels of building air-tightness — and little details can have a big impact.
6. Constant communication and collaboration are required
Because the methods and materials used in building high-performance homes are sometimes unfamiliar to trade partners, strong communication and collaboration practices are crucial to success. Everyone agreed that insufficient communication, both between the builder and trade partners, and within the trade partners’ organizations, was one of the biggest barriers to overcome when constructing the lab home. This was addressed, in part, by including the trade contractors upfront in the planning and design process, which was a major focus of the project.
Trade partners that were expected to overlap and interact during construction were brought in to the IBACOS headquarters to participate in training and the development of mock-up assemblies. For example, not only was the HVAC contractor part of the HVAC system planning process, but so were the plumbing, electrical, and ground-source heat pump ground-loop contractors. Engaging with the trades made them feel like part of the process, and we learned as much from them as they did from us.
7. Evaluate partners before you begin
Subcontractors don’t always need to know a specific skill going into the construction process, but they must be willing to learn. The lab home’s first siding contractor was skeptical of installing siding over the foam sheathing on the exterior of the wall, partly because the manufacturer wouldn’t warranty the job — manufacturer standards required fastening 16 inches on center, rather than the 24 inches on center that was necessary because of the furring strips. Despite agreeing on how to execute the installation, the installers reverted back to their standard practices, placing some nails through the foam. After repeated attempts to explain the importance of the specified details, the decision was made to have another installation company complete the job.
8. Management buy-in is crucial
Communication will help, but if the resistance to change and collaboration is coming from upper levels of management, it may not be enough. If a contractor’s management team is not committed to improving the performance of the homes they build, then the field crews are less likely to engage in or learn from the experience. In contrast, the managers from both the geothermal ground-looping and plumbing trade contractors understood the educational and marketing benefits of being involved with a project like the lab home, which resulted in a high level of cooperation and field crews viewing the project as an opportunity to learn.
9. Don’t beat up your trade partners
It’s important to remember that with the downturn in the housing market, many trades are suffering. When you ask them to change a building process, you need to remember that they are sometimes doing so with a significantly reduced staff, reduced capacity, and often at no additional cost. You can improve the chances of buy-in by showing a little love — perhaps even compensating them for the additional time required for the learning curve with the first few high-performance projects, while being clear with your intent for standard pricing moving forward. Always trying to get more for less may succeed in the short-term, but can backfire in the long-term.
10. In-field supervision is critical, especially with first-timers
Even after the upfront planning and scopes of work have been agreed upon, some trade partners may still cut corners and make field adjustments without securing approval, impacting the quality and performance of the home. Having a presence on the job site and coaching the trades will help, especially early on in the learning process, but vigilance is key.
For example, prior to construction, IBACOS did a test run with the management and field crews of the insulation contractor and representatives from the insulation manufacturer in order to identify best-practice techniques for installing blown-in fiberglass in the thicker, 2x8-inch wall. Everyone agreed on a method that would result in the desired insulation density and R-value, but when it came time to install, the crew needed additional attention and coaching to prevent inconsistencies.
The key was to have supervisors there to answer questions and provide guidance while the trades were implementing something new.
Kevin Brozyna is a project manager with IBACOS, a research and services firm based in Pittsburgh. Brozyna provides technical assistance to production-minded builders who are striving to build to higher levels of energy efficiency. He is a NAHB certified green professional and works to define green metrics within IBACOS Research programs.
Fitting in: Building a zero-energy home in a typical neighborhood
The Best Practices Research Alliance’s Energy Efficiency Lab Home was built in a typical residential development and looks similar to any other home in the community. That’s partly because of the Alliance’s goal of making net-zero-energy homes affordable for production builders to construct.
The home’s design is also the result of constraints imposed by the developer, who wanted the house to blend in with the community. Those constraints included requiring the use of vinyl siding, brick, or stone cladding and an asphalt-shingle roof with no unusual overhangs or audacious design features. Using vinyl siding rather than, for example, fiber cement, required the exterior wall surface to be flat. If fiber cement had been used, it could have been installed over surface-mounted furring strips using a rain screen technique. But the vinyl forced the project team to develop a wall assembly that would support the back of the siding, which resulted in the use of the exterior foam sheathing and recessed furring strips. This approach also provided the benefit of using lower-cost framing nails rather than more expensive screws to attach the furring strips to the wall.
In addition, the team was required to locate high-performance, triple-glazed windows that would match the single-hung style of vinyl windows that were used in the rest of the community.
At first, the developer objected to the idea of using solar panels anywhere on the house or lot because they felt the panels would draw too much attention to the home. But after providing the developer with renderings of the house to show what the panels would look like, they agreed to allow them on a portion of the roof. Discussions with the developer also helped them fully understand the benefits of using naturally vegetated landscape areas that require little maintenance, rather than requiring turf grass throughout the lot.