How To Get a Blower Door Under 1.5 ACH for the New All-Electric Homes Program
The Sponsors of Mass Save have launched a new incentive program to drive market transformation in residential new construction toward high-performing, all-electric homes. They are offering incentives (Tier 1) of $15,000 for single-family homes and up to $22,500 for multi-family buildings (up to 4 units) to support builders, developers, and homeowners in the construction of new homes that will use substantially less energy than code-built homes, while providing enhanced comfort and long-term resiliency.
There are 7 requirements to qualify a home or building for this new program and one of them is having a blower door test below 1.5 ACH (Air Changes an Hour). Massachusetts building code requires 3 ACH (2018 IECC & Mass 780 CMR .51 9th Edition Energy Rating Index. Achieving 1.5 ACH requires a strategic insulation package and a detailed air sealing plan. While a builder has several options to achieve this level of airtightness, two options are most prevalent.
The first is to spray foam the entire roofline all the way to the peak, creating a hot roof that will not need vented soffits or a ridge vent. The above-grade walls are insulated with fiberglass batts, mineral wool, or spray foam depending on the builder/homeowner’s preference. The final step with this method is to insulate the entire foundation. Commonly, this is done with closed cell spray foam, open spray foam, a hybrid mix of low and high density, or rigid insulation. Keep in mind the vapor retarder, Fire Code requirements, and how the municipal ISD enforces those are also part of the code.
The second way of achieving 1.5 ACH is to insulate the framed floor to the unconditioned basement with R30 batts, insulate the above-grade walls with fiberglass batts, and insulate the flat ceiling to the attic with either blown-in cellulose, fiberglass batts, or blown-in fiberglass (depending on cost and availability). This method will have a vented roof, with soffit vents and a ridge vent. Smaller, vaulted ceilings can be insulated with either fiberglass batts or netted and blown cellulose or fiberglass. However, this insulation package on its own will NOT achieve 1.5 ACH. The final step with this method is using Aerobarrier to seal the building envelope after sheetrock and plaster, but before any finishes go in. AeroBarrier is an interior applied air sealing system that simultaneously measures and seals all building envelope leaks up to 1/2″ allowing builders to “dial in” the precise level of leakage and performance quickly and easily – a must for this new program. More information about the Aerobarrier product and process can be found at www.neairbarrier.com.
Between these two methods, builders have options to achieve this level of airtightness depending on project budget and/or personal beliefs about hot roofs compared to vented and long time degradation of roofing compotes due to a lack of venting. Properly sized and commissioned exhaust, supply or balanced ventilation systems are possibly the most important aspect of a low infiltration home. We will discuss that topic in a future article.
To learn more about the new All-Electric Homes Incentive Program and it’s requirements, click here.
If you have questions about this new program or are interested in enrolling an upcoming project, please reach out to our All-Electric Program lead, Andrew, at email@example.com.