Can the blanket Insulation in my basement be left in place when refinishing?

Question

I'm thinking about finishing my basement. It currently has the blanket insulation that the builder installed when we built the house last year. I'm unfamiliar with this product. Is it meant to be used behind my framing or should I take it out and use something else. I would love to use it since I already have it.

Matt G · Accepted Answer

If the exterior of the foundation has the black waterproofing membrane, you're fine to build your framed wall right up to the vinyl blanket insulation in the basement. When I finish basements for my clients, they always ask my opinion. Here it is: I don't like spending money twice. If there is already insulation on the wall the meets the code requirement, then we'll frame right to in and leave it in place. The white vinyl insulating blanket usually has an R value of 10. In Colorado where I live and work, that's the code requirement. You won't see a lot of thermal benefit from upgrading the insulation to a R-13 or R-19. To me it's not worth the cost of removing and replacing. (not to mention the disposal of the blanket - it takes up a ton of dumpster space!) That said it would be easy to add batt insulation in addition to the current insulation after you frame the walls. 
One note: you do not want to compress the vinyl blanket with the wood framing or you'll reduce the effectiveness. If you do compress it, take a knife blade and run it down both sides of each stud and it will allow the insulation to expand into the stud cavity.

Your main source of heat loss in the basement is going to be around the  windows. Take the time to seal the windows well.  Hope that helps!

Jack · Answer

Yes you can but it can be the only layer, and I would draw concern with the R value the blanket has. It may at best only have an R value of 5, maybe more, and perhaps that is enough. For reference, foam board on the average has a R value of 5.5 per inch

If your basement has a bit of exposure above the outside grade, and you get really cold winters, I would truly consider upgrading your insulation. Insulate the whole wall too if not already done. Some codes may allow only the top of the wall needing insulation, down to 2 ft. below grade. Basement walls conduct the cold very well and an exposed part of the wall will still radiate the cold

The link that DAO1 has, uses good procedures for a basement install, and as he cautions, do not layer insulation with vapor barriers, there can only be one toward the heated side, an additional vapor barrier will trap moisture and cause problems.

Eric Gunnerson · Answer

If I was finishing a basement these days, I'd pull out the current insulation and have somebody come in to shoot a few inches of foam. That gives a nice monolithic insulation blanket.

The best reference I know on these sort of things is BuildingScience.com They do lots of research and have great articles on how to do things right.

Ryan · Answer

After 2 years we had mold behind the blanket on our North wall that is above grade.

BMUSCOTTY · Answer

I've installed basement blanket in 5000 homes in the past 20 years. The fact is that basements need a Tyvek or Typar layer installed prior to the Blanket insulation. Any other then that and you're taking a chance of major moisture problems in your basement along with that damp smell that most basements have.

If it were my basement I would:

Remove all blanket and insulate in joist pockets 
Use can foam spray and pipes ducts vents leading to the outside; spray any gaps between sill plate and foundation any tie downs
Tyvek all exterior walls with Tyvek / Typar
Frame walls 1 inch off foundation walls
Insulate with R22 Roxul 
Put R44 in joist pockets
Caulk top plate, bottom plate, corners and every double stud (this is a crucial step) 
Apply Vapour barrier

Can the blanket Insulation in my basement be left in place when refinishing?

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