Spray foam questions
There is a possibility that a design-build client will opt for a spray-foam insulation package to include living area exterior walls, attic gable walls, and attic rafter cavities / decking. This home has atypical attic space. I have never had a client request this before.
As I have read and understand to date:
1. Spray foam creates a complete envelope, being sprayed in the walls, to include attic gable walls, and the roof deck / rafter cavities.
2. Even though there are typical “attics” that are not scheduled for HVAC ducting / acclimatization, no separation by additional insulation or air barrier between the attics and the living area below is necessary.
3. One recommendation is to establish an air barrier between the spray foam on the roof and roof decking. (Unanswered response: Could this mean the installation of a ridge and soffit vent?)
4. Spray foam can become a nesting place for insects , with an example from a user being infestation of carpenter ants who tunnel into the foam……..consequently borax treated foam is recommended.
5. There are a variety of spray foam compositions, greenbuildingadvisor.com cautions that some spray foams have “out gassing” problems.
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Replies
John,
And your question is...?
1. Spray foam creates a complete envelope, being sprayed in the walls, to include attic gable walls, and the roof deck / rafter cavities.
Spraying foam on the exterior of all sheathing surfaces may create a complete thermal/air barrier envelope. But foam interrupted by framing members does not an envelope make. There must also be continuity at all assembly junctions.
2. Even though there are typical "attics" that are not scheduled for HVAC ducting / acclimatization, no separation by additional insulation or air barrier between the attics and the living area below is necessary.
That's the theory - either stop the thermal envelope at the attic ceiling or at the roof plane, depending on use of attic space and the most effective method for continuity of barriers.
3. One recommendation is to establish an air barrier between the spray foam on the roof and roof decking. (Unanswered response: Could this mean the installation of a ridge and soffit vent?)
And air barrier is exactly that: a barrier to the movement of air through a building envelope. A vent is the opposite of that: a matched pair of openings and a channel for air passage. Two different things - to different functions.
4. Spray foam can become a nesting place for insects , with an example from a user being infestation of carpenter ants who tunnel into the foam........consequently borax treated foam is recommended.
Any foam that isn't treated with insecticide is vulnerable to insects and to rodents as well. That's one of the many vulnerabilities and liabilities of foam insulation.
5. There are a variety of spray foam compositions, greenbuildingadvisor.com cautions that some spray foams have "out gassing" problems.
Any two-part catalytic foam can have outgassing or other problems if the mix isn't properly proportioned and the atmospheric and surface temperatures aren't within limits. All plastics lose their plasticizers over time.
John.... get the spray contractor with the most years in the business and go see happy customers... call them... go to a spray site or two. If he is good he can give you all the info and a proper spec for your project. Make sure he does residential homes. Hundreds... not dozens.
I only trust one in my area.