Cellulose batts over fiberglass in attic
user-7245550
| Posted in General Questions on
can I install cellulose blankets in the attic over blown in fiberglass or will this cause a moisture problem?
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Replies
Hi user-7245550 (Would be nice to know your real name).
I doubt that this would cause any problem in your attic. However, batts are meant to be fit into tight spaces and blown in insulation if meant for these applications. If you don't already have the batts, consider blown in cellulose instead. Also, consider doing some air sealing in the attic if you haven't already. You could be wasting your time adding insulation if you don't have a tight ceiling and closed off thermal bypasses. Check out this article for more info: How to Insulate an Attic Floor
Is the question to blow cellulose over fiberglass batts, I think it most likely is. This is a good opportunity to air seal the attic bypasses as Brian said. I had fiberglass batt insulation in my attic from the original 1978 build, 12" R-38. I peeled back the batts and sealed along interior walls, wire penetrations and plumbing stacks. The ceiling has polyethylene so I worked the edges to get a good seal to the plates. Adding or extending the air chutes should be done at this time. Once the air sealing was complete I rolled the batts back in place and had an additional 24" of blown fiberglass put in for a total R-value of about 100. At least the ceiling of this house reaches Passive House standards.