How to insulate attic with vermiculite?
Hi, I’m back with another question. I live in Maryland and want to retrofit my house, built in 1938. I’m focusing on the attic. My attic has vermiculite, so I have to assume there is asbestos. Five years ago we decided to insulate the attic and the recommendation we heard sounded good, that it was best to lay fiberglass over it. So we did that – but incompletely; the space between the gables has a plywood walkway about 4 ft across that is sufficient for storage and attic access, and remains uninsulated, a river in a sea of R-30. Also, although the penetrations were sealed, the tops of the inner wall partitions were not foamed. So I assume there is leakage that could be improved. What is the best way to finish the attic?
The attic space is fairly small, only about 5ft at the ridge and tapering down to meet flush with the exterior walls. It is unvented save for small windows on the gable ends. I have no ducts and no plan for HVAC in the attic (except maybe a whole house fan in the future). But storage space sure is useful. If I insulated under the rafters, would I remove the fiberglass on the floor – at the risk of disturbing the vermiculite – or simply leave in place? Finally, I have read about the various options for under the rafters except for Air Krete. What is the assessment on Air Krete under the roofing deck or on the attic floor? The manufacturer tells me that both theoretically work, although they would not generally recommend under the rafterswithout a soffit and ventilation channel under the sheathing; and that on the floor it could be poured over the vermiculite to fix it in place.
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Replies
I should clarify what I meant by "theoretically." The manufacturer has used Air Krete on both rafters and attic floor and offer this. I meant both were therefore theoretically feasible, although in my case the lack of a soffit would go agains their usual practice and they would have to search for some alternative method of ventilating. They attach Tyvek wrap to the underside of the rafters and then spray the cementitious material to lay on top, leaving an air gap between the Air Krete and the roof sheathing.
You ask, "What is the best way to finish the attic?"
Does that mean you intend to convert your attic into finished interior space?
Sorry. Ambiguous choice of words. I meant how to finish air sealing and insulating. I don't need finished interior space. However, I would like to maintain some space for storage. I have been told that the vermiculite would be my air barrier, so all I need is insulation. Do you agree? This is my primary question.
Richard,
Your question is easy to answer. Vermiculite is never an air barrier. It is very air-permeable.
My advice: don't touch the vermiculite if you can avoid it. If you decide there is a need to disturb the vermiculite, don't do it yourself. If the insulation needs to be moved, hire a certified asbestos abatement contractor to dispose of the vermiculite.
Martin,
Thanks so much.
Richard