Flash-and-Fill Insulation in Attic
We just moved into a house built in 2005. It is insulated in the attic with spray foam on the ceiling drywall (not the roof-line) to what was suppose to be an R30 2003 IECC standard. The current standard is R49. This house is the same square footage (3000) and gets much hotter than our previous home which had blown cellulose to an R36. After further inspection, it appears that there is only 5-6 inches of foam in some areas and other areas its only 3.5-4″, which at R3.5 per inch for open cell foam is only an R15-R20.
So, is there a problem or advantage with blowing cellulose over the existing foam in Northwest Arkansas Zone 4 (we’re on the border of zone 3 & 4)? Costs for increased foam seem prohibitive and not something I can DIY. Any other options?
Supply ducts and 1 return duct are in sealed basement crawlspace – 1 return duct is in attic. Thanks. Mark
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Replies
Mark,
There's no issue with installing cellulose over existing foam in a vented attic. Just make sure to keep a ventilation gap clear at each eave bay with baffles, and make sure the return duct is well air-sealed and insulated. The existing foam acts as a great air seal. Cellulose on top of foam is sometimes called "flash and fill". Works great.
That said, I don't suspect upgrading from R30 to R49 will drastically change your heating and cooling demand. I would do it anyway, but you really won't "feel it".
Hi Mark,
The flash-and-fill method that Jason referred to is a variation on the flash-and-batt approach described by Martin Holladay. He provides code-related information and resources that may be helpful for your situation.