Moisture Behind Plastic Test Strip in Basement

Updated: April 25, 2023


I am wanting to finish my basement. The basement is fairly dry, I have never seen water down there and the walls only get a little wet if the horizontal piece of the downspout that diverts water away from the house falls off. Occasionally in the spring when the snow melts the block wall gets a little damp in certain places. The house was built in 1992.

I tested for moisture in the basement by putting some EPS foam on the wall and sealed it, then checked a couple days later to find the block behind the foam was damp. Is this normal or should I attempt to fix that condensation issue before insulating the wall? My plan is to insulate with 2" EPS foam glueing it to the walls with foam board caulk and spray foaming the seams.

The wall will be 2x4 pressed against the EPS, the bottom plate will be green treated with a foam sill seal. The space between the joists will also be 2" EPS foam and all the seals will be spray foamed to form a tight barrier between the concrete and the interior. The stud walls will be insulated with unfaced insulation and then drywalled and painted. I know there will be moisture between the concrete block and the EPS. Is this bad or a normal part of this design? There is a drain tile that runs into the sump in the basement, only time it runs is a trickle in the spring.

I do not believe the exterior block wall has been protected with a waterproof membrane or foam. If I needed to add something to the exterior, what would you recommend? 

Thanks for your time and help,


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