Going to finish basement of new (to us) home. Built in 80's. Has a fibreglass blanket currently going half way up the concrete.
Would it make sense to remove it all, add 3" rigid foam, then frame and add some more insulation?
It seems dry, not much black (only in a couple of areas but light).
We always remove the existing fiberglass. Then install r-ridged foam insulation. Be sure to cut and fit it everywhere. Including all the spaces between the floor joists. Then use Tapcon tape on every seam. Then frame your exterior walls. Finish all wiring in these walls as well as any plumbing work. Then install r-20 green bat insulation. Then you can apply your drywall.
Enjoy your new finished space.
From a different perspective and contrary to previous practices, I would not put the vapour barrier on the house side, since there is usually a higher level of moisture on the foundation side than can be found on the inside of the property. By putting vapour barrier on the inside, you are effectively trapping moisture between the vapour barrier and the foundation wall, thereby promoting and facilitating mould growth.
The other thing I would not do is put roofing felt (tar paper) on the foundation walls as this readily promotes mould growth in the presence of the moisture and humidity that permeates through the foundation wall. This is especially true with cement block.
If you put your impermeable barrier on the foundation side, then your insulation and drywall on the room side it will allow the insulation to breathe and thereby stay dry.
We have removed more mould affected roofing felt and insulation than I care to remember just because it was done the same as it has always been done, the vapour barrier on the warm side, instead of on the wet side.
The 3 inch rigid foam is a good idea as it will act as a vapour barrier and insulation at the same time, then you can put your 2 x 3 or 2 x 4 studs in front of that. The only recommendation is to make sure that you tape, or otherwise seal your joints between the sheets of insulation. Adding more insulation on the room side of the 3" styrofoam will give you quite a kick in the energy saving side of things.
the 3" foam, if it is StyroFoam SM will give you R15 and the batt (if you go 2 x 4 walls and Roxul), could give you and additional R14 for a total of R29 in the basement. No sure if you need that much in the basement.
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