Attic Insulation
SpiderfromMars
| Posted in General Questions on
Since reading a BBC article about U.K. insurers not wanting to insure houses with foam between the rafters and, as a former insurance risk manager, my attic insulation plan has changed.
There is no insulation in this c1890 house.
My question is regarding Owens Corning 2″ x 4′ x 8′ styrofoam panels – can I stack them 4 high on my wood decked attic floor?
Can I then used 1/2″ 4′ x 8′ plywood on top of the panels for storage?
This is an unconditioned, vented attic.
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Replies
Just use loose fill insulation with a "deck" over it. That's cheaper. Next best would be batts and a "deck". I wouldn't use rigid foam insulation on an attic floor like this -- it's more labor to install, and it's more money for the materials.
If you're not in the UK, I wouldn't worry about spray foam and insurance. The US and Canada are both fine with sprayfoam, and the risks are overstated online. The vast majority of installations are completely trouble free. In your case though, I wouldn't use spray foam anyway, since in a vented attic, there are cheaper ways to insulate the floor that perform just as well. I would use canned foam (which is NOT spray foam) to air seal prior to insulating.
Bill
Matt Risinger did a video 2 weeks ago that covers this exact issue: https://www.youtube.com/watch?v=hCZgv4K5aTk
Long story short, folks are slapping up some spray foam between the rafter bays, but not going all the way to enclosing the attic into the living space. The result is potentially dangerous knock-on effects, especially relating to moisture (both from rain and from condensation). It's not the material that's the problem, but the execution.
In your case, if you're keeping the attic unconditioned, it's essentially an outdoor space, albeit shielded from most of the weather. Insulating the living space, as you say, shouldn't be a problem.
I found the Risinger video really click-baity. Just the title, "Major Lenders Reject Homes with Spray Foam Insulation" without noting that it's only in the UK. "A quarter of all mortgage lenders in the UK won't lend" sounds dire, but banking is much more concentrated in the UK, there are only 340 lenders.
That said, I disagree with your assessment of what he found: "Long story short, folks are slapping up some spray foam between the rafter bays, but not going all the way to enclosing the attic into the living space. The result is potentially dangerous knock-on effects, especially relating to moisture (both from rain and from condensation). It's not the material that's the problem, but the execution."
What he points to are thin layer of open-cell foam, poorly installed with significant gaps and poor adhesion. Nothing to do with "not going all the way to enclosing the attic into the living space." As to "It's not the material that's the problem, but the execution," yes, the execution is poor but the use of open-cell foam instead of closed-cell is a material problem.