I'm currently in the process of remodelling my basement. When I took all the drywall down, I found that water was coming in through this gap between the top of the concrete wall and the wood framing.

How would I go about waterproofing this gap?

I know to fix the problem from the exterior is to grade the water away from the house, but would like advice on how to handle the problem from the interior as well.

Picture of gap between top of concrete wall and framing

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    – isherwood
    Jul 26, 2022 at 14:50
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    Jul 26, 2022 at 15:36
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    Jul 27, 2022 at 12:12
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    – JosephTJC
    Jul 27, 2022 at 12:57

3 Answers 3


I am currently working on sealing and insulating my basement rim joists and sill plates as well. I mostly followed a similar strategy as this (minus the fiberglass): enter image description here But I am using more spray foam behind the rigid foam board and along and between the floor joists. I am also building up some gaps between concrete and sill with hydraulic cement but only in places where water had eroded it significantly, which I don’t see much much of in your photo.

Using spray foam for the entire job might be ideal, but this is quite expensive.

This method is working well in my case so far, but is time intensive and, to be honest, the most significant improvements I have seen have been from correcting the soil grade outside.


The question I see is how to support a wall with nothing directly above.

Add nailers short sections of 2x4 or 2x6 to bridge between joists one at each end and every 16-24” along the length of the wall.

It’s not structural just a top anchor using 24” has the points not at a wall stud so easy to nail or screw and the wall will be stable.

I like to use sill seal foam under the bottom plate and although a pain I cut segments where I leave a 1” gap incase of water this allows the water to move and not be trapped.


The best place to waterproof any wall is on the outside.

That mean you're going to have to figure out how the water is getting to that crack and fix that. else your framing is going to get wet and thats not good unless you're building a pier.

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