NOTE – It is very important that we inspect the airseal before the walls are closed up. This gives us the opportunity to find and address any specific issues while the walls are open.
It is very difficult to make repairs if the house does not pass the blower door test at the time of the final inspection, long after the walls have been closed up.
NYBTG recommends the use of spray foam as insulation because of its superior airsealing capability. However, because of its cost, it is not practical for every application.
If you are using batt insulation alone, there are several areas that require extreme attention to detail when airsealing, and a few situations where fiberglass can never be used alone.
Spray Foam
Spray polyurethane foam (SPF) insulation is an advanced, energy-efficient, and air sealant capable product. There are a few product options available depending upon the intended application.
- Closed Cell – A hard, vapor-resistant foam that may be used to airseal a home.
- Open Cell – Offers the same insulation benefits as closed cell foam but does not act as a vapor retarder or barrier.
ATTICS: It is becoming common to create a “sealed attic” using spray foam insulation in the rafters rather than in the ceiling.
This has two benefits:
- It moves attic HVAC equipment into the thermal envelope which eliminates losses from the equipment.
- It also adds additional conditioned volume to the home allowing blower door testing and compliance easier to achieve.
Fiberglass Batts
Batt insulation is one of the most common and cost-effective insulating methods. It provides basic coverage in homes in floor, wall, and attic cavities. It is a quick, affordable, and sound dampening option.
We have run into situations where builders have insulated both the ceiling and the rafters in an effort to keep HVAC equipment “inside conditioned space”. Again, unless the roof assembly is insulated, properly vented, and air-sealed, it will not meet NYS code and will likely have serious moisture and mold issues.
FIBERGLASS BATTS ALONE CANNOT BE USED FOR A SEALED ATTIC:
- The IECC requires that fiberglass batts in a roof rafter have a ventilation space but also requires that the insulation and airseal be aligned.
- Without drywall on the assembly (as with a vaulted ceiling) there is no airseal keeping air from the home from escaping out through the ridge and soffit vents.
Flash & Batt
Why not both?
The combination of high density spray foam used within cavities first followed by batt insulation is becoming a more popular method for insulating a wall assembly.
- A minimum of two to three inches of high density spray foam allows the cavity to become air sealed while doubling as a vapor retarder.
- Batt insulation added in following the spray foam layer increases cost savings for the project to meet wall assembly R-value requirements for code compliance.
