RECOMMENDED MEASURE – ATTIC SEAL PACKAGE
In a new construction home project “attic seal package” is the process of applying closed cell foam across all air leakage points from house to attic. This could include across all top plates, framing gaps over dead spaces and fireplace, over pocket doors, around wire, duct, and plumbing penetrations, at ceiling height transitions, etc.
The primary benefit of this measure is to prevent cold-climate wintertime frost from forming on the underside of the roof decks and then melting and dripping back into the house. Frost shows up in the attic when moisture-laden air from the house gets into the attic. That's about it, pretty simple. When the moisture gets into the attic, it condenses on the roof sheathing in the form of frost. The frost itself doesn't do any damage, but once it melts things get wet, which is when the damage occurs. Melting frost can lead to deteriorated roof sheathing, mold on the roof sheathing, wet insulation, and water stains on the ceilings. All bad stuff; you definitely don't want frost is your attic.
The best way to prevent frost from accumulating in an attic is to seal off attic air leaks. While seemingly small air leaks may not seem to be important, these can add up to a lot of frost accumulation in the attic. It's important to seal all attic air leaks; not just the big ones. Once every little air leak has been perfectly sealed, the attic will be frost free.
The air in your house sees your house as a very wide chimney, because warm air rises. The taller the house, the greater this effect. Code-required make–up-air makes this worse because when the furnace runs the house is pressurized which increases the effects of attic air leaks.
More insulation doesn’t help: if an attic doesn't have enough insulation, it will be warm. Adding insulation will make the attic colder. The colder it is in the attic, the greater the potential for frost accumulation.
Adding additional attic venting: rarely helps and sometimes can make the problem worse.
Besides frost and moisture in the attic, additional benefits of this measure include:
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More comfortable house
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Reduces potential for ice dams
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Saves on energy bill
