Top 10 Lessons From Building a Net-Zero-Energy Home

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August 16, 2011

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.

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