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Christopher Campiglia Posted: Dec 11, 2008 06:39 PM	Spray Foam and Flashing I have heard from several people that because the cost to spray foam their homes is expensive, they have opted to spray foam 1 to 1 1/2" of closed cell foam, and then use fiberglass insulation to meet the building code. Is this beneficial, and if not, what problems can arise?
mason Posted: Dec 12, 2008 07:21 AM	This practice (called "flash and batt" can be used successfully in warm and mixed climates with 1 to 1.5 inches of closed cell sprayfoam. The foam air seals the wall or ceiling cavity reducing the potential for moisture condensation and allowing the fiberglass to perform more efficiently. On the negative side, some convective currents can occur in the fiberglass reducing its overall efficiency, just not as much as if the foam was not there. However in colder climates, you would want to guard against moisture drive from the inside condensing against the foam. 2 to 2.5 inches of closed cell foam would prevent this from occurring in most climate zones in the US and southern Canada. Some suppliers are promoting flash and batt systems using 1 inch of closed cell foam in colder climates by installing a vapor retarder to the fiberglass. This can work but it must be perfectly installed without tears, rips or holes that would allow moisture vapor into the wall or ceiling cavity.

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Comments

Christopher Campiglia

Posted: Dec 11, 2008 06:39 PM

Spray Foam and Flashing

I have heard from several people that because the cost to spray foam their homes is expensive, they have opted to spray foam 1 to 1 1/2" of closed cell foam, and then use fiberglass insulation to meet the building code. Is this beneficial, and if not, what problems can arise?

mason

Posted: Dec 12, 2008 07:21 AM

This practice (called "flash and batt" can be used successfully in warm and mixed climates with 1 to 1.5 inches of closed cell sprayfoam. The foam air seals the wall or ceiling cavity reducing the potential for moisture condensation and allowing the fiberglass to perform more efficiently. On the negative side, some convective currents can occur in the fiberglass reducing its overall efficiency, just not as much as if the foam was not there.

However in colder climates, you would want to guard against moisture drive from the inside condensing against the foam. 2 to 2.5 inches of closed cell foam would prevent this from occurring in most climate zones in the US and southern Canada. Some suppliers are promoting flash and batt systems using 1 inch of closed cell foam in colder climates by installing a vapor retarder to the fiberglass. This can work but it must be perfectly installed without tears, rips or holes that would allow moisture vapor into the wall or ceiling cavity.

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