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Installing rigid foam insulation with a French drain

Smoke Teff | Posted in General Questions on


Another question about insulating my basement in Philadelphia. We recently had a French drain installed along one of the walls. The plumbers attached a dimple mat about six inches high at the bottom of the wall. Should I extend this to the top of the wall underneath the rigid foam board insulation I plan to install?

Also, there is not much room between the drain pipe and the wall–enough room only for a 1/2″ foam board (when I was planning to use 2″ foam board elsewhere). Should I use a thinner foam board for that wall for the sake of fitting it behind the pipe? Or should I use a thicker foam board but just cut it so it doesn’t go all the way behind the pipe?

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