Which is the best foam board insulation to put against poured concrete basement walls?

Patricia Roberts
Updated: Dec. 28, 2021

I have read and read until I am blue in the face with a migrane! I'm thinking/ hoping that I've finially gotten the insulation aspect of finishing our basement correct, but I'm still not sure. The two different kinds of foam boards I've been looking at are, Kingspan Insulation R-10 2in*4ft*8ft unfaced polystyrene foam board from Lowes and the Foamular 150 2in*4ft*8ft R-10 unfaced squared edge insulation sheathing from Home Depot. Are either of these two efficient and effective? We have baby number 4 due in March. We're on a tight budget, but also do not want to suffer the consequences of mold at a later date. 

Also wondering if I should use drylok waterproofer paint on the concrete before applying the insulation board. I've read so many contridictory things from so many websites and forums, I am at a loss. 

Thanks so much for the help!


Responses (3)

Patricia Pfeffer
Patricia Pfeffer 2 years ago

We live in KY, USA. With our basement being completely underground it actually stays quite warm in the winter and cool in the summer and that's with it being completely unfinished right now, so I'm honestly not super worried about the r value and more about the mold factor, as two of our kids bedrooms will be moved down there. 

Would you also use waterproof paint on stuff before applying the foam board, or not bother with it at all?

Mike Reynolds 2 years ago

No I wouldn't bother with the paint. the foam will be waterproof enough. mold happens when people put wood against concrete and then seal it in with a sheet of plastic. You should have no problems. have you ever experienced flooding though? if you're going to the effort to finish it, it might not hurt to stick a sump pump to protect against flooding if there has ever been any. The weather is only getting more unpredicable and more severe so you never know. 

Other things that help prevent flooding and even mold, is reducing the amount of water  around the foundation, so things like eaves troughs that drain far from the foudation and being sure that the ground slopes away from the house not towards it.