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Old 05-19-2017, 11:19 AM  
soparklion11
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Default Insulating basement with interior french drain and vapor barrier.

I own a 1940s home with a basement. The walls in some areas of the basement were bowing, which is common here in western Pennsylvania (zone 5) due to wet soil and collapse of the terra cota exterior footer drainpipe. Sooo we all get interior french drains...

I want to furnish the basement again by framing, hanging drywall and placing an engineered wood floor.

I now have an interior french drain with only a few inches of concrete over the drain trough. The drain was installed 2.5 years ago and there has never been water in the sump. There is a plastic vapor barrier nailed against the wall with plastic washers. The sump sits 5inches from the foundation wall, so I don't have a tremendous amount of space for insulation. The gap between the sill plate and the studs is ~1.5 inches at the base, but 3/4" where the wall bows inward - note that there are carbon fiber straps that limit wall movement.

How should I insulate the basement? I see options as open cell spray foam on the vapor barrier or fiberglass bats in the walls with a gap between the bats and the vapor barrier. I don't have space for XPS unless I relocate the sump or figure out some way for that last 2 feet of wall not to cover the sump...

Without insulation, will I have condensation on the room-side of the drywall? It can be very humid here.



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Old 05-19-2017, 09:31 PM  
nealtw
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We build all basements in as discussed in other thread and the 3 1/2" insulation between studs. and vapour barrier just behind the drywall but as you have plastic on the wall already you don't need two.

If you have forced air furnace you will want to increase the return air in the basement. That should help with humidity. And make sure you have fresh air for fire air for the furnace.


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Old 05-20-2017, 08:02 AM  
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Do the 3.5" insulation and the studs end up damp and moldy with a barrier under the drywall?
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Old 05-20-2017, 08:20 AM  
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Quote:
Originally Posted by soparklion11 View Post
Do the 3.5" insulation and the studs end up damp and moldy with a barrier under the drywall?
More often the moisture comes from the living space, and the barrier is there to stop airflow
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