Can both sides of a foundation wall be insulated with styrofoam?
I live in a home built in 1957 in Montreal Quebec. I am renovating my basement and decided to spary hight density foam in all the inside perimeter, a few days ago I notided a small crack outside at the bottom angle of a window, and decided to excavate to the footing, the crack goes in a U shape from one window to the other passing under the front door, about one foot above the footing. that is one problem that will fix with a polyurethane injection and a steel plate,, the other problem is that there is no footing made out of concrete but it is just a rock slab with the founddaiton falling straight on it. between the fondation and that rock slab there is a gap of 2 to 3 inches thats full of clay like mud. looks like the conrete has washed off permitting clay deposit in between. I was thinking of removing maybe 4 inches of clay filling with cement then apply a liquid mambrare and 2 inch pannels of styrofoam to protect the liquid membrane. Is that possible given that I have already applied liquid styrofoam by the inside? the foundation continues almost 5 feet above ground, my home is a 1957 duplex.. so im guessing that humidity would escape through those 5 feet above ground that wont be insulated but not sure. Whats your opinion on that? Thanks!!
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Styrofoam is a trademark owned by Dow Chemical for their extruded polystyrene (XPS) product lines. What is "...liquid styrofoam..." ??
Insulating the below-grade exterior of a foundation with polystyrene foam is fine, no matter what is on the other side of the foundation wall. From a thermal performance point of view insulating the above grade portion of the wall (on either the interior, exterior, or both) is more important than below grade. But with 5' of above grade exterior exposure the wall can readily dry toward the exterior, and the foundation sill & band joist will not be at risk even with very low permeance insulation on the interior.
If there is going to be low-permeance foam insulation on both sides of the wall right up to the level of the foundation sill it can still work, profided a good capillary break (such as EPDM sheeting) between the concrete & wood. Concrete tolerates moisture well, but the wood doesn't.
Insulated concrete forms (ICFs) typically use 2.5" of EPS on both sides of the foundation wall without high rates of moisture failure at the foundation sill even with fairly crummy foamy sill gaskets using pressure treated lumber for the sill. But if you're going to retrofit something in a house where the foundation sill is probably untreated wood it's worth using better materials.
I'm guessing that "liquid styrofoam" means "spray polyurethane foam."
Marco,
In almost all cases, encasing a concrete wall with foam insulation on both sides does not cause any problems. As Dana noted, insulated concrete forms (ICFs) have EPS insulation on both sides of the concrete.
Dana also correctly noted that concrete does not need to dry. It can stay wet forever.
There is a small concern that in an older house without sill seal between the top of the foundation wall and the mudsill, the damp concrete might cause rot in the mudsill. (Since your house was built in 1957, the sill isn't pressure-treated.) The perfect solution, rarely done, is to jack up the house 1/4 inch so you can slide metal or rubber flashing between the foundation wall and the mudsill.
Most people ignore this step and don't have any problems. That said, if your foundation is unusually damp, you should be aware of the risk.