Foam board insulation and dimple board
TooldadNJ
| Posted in General Questions on
If you want to use 1 or 2” foam board insulation on basement walls with a french drain in place with a dimple board, where does the foam board go? Behind the dimple board? Laying atop the dimple board? Do you use spray foam to fill the gap between the two? This is interior application
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Replies
TooldadNJ,
There is a difference of opinion between experts, so your choice. This blog lays out the upsides and difficulties of the two options:
https://www.greenbuildingadvisor.com/article/using-a-dimple-mat-to-keep-a-basement-wall-dry
thanks. i read that but it wasn't clear how this pertains to interior installations and where the foam board should fall.
You did not mention it was interior
Deleted
I used dimple mat against the block wall in a few areas of my own home, then used foam board over that. You need the dimple mat directly over the foundation wall if the intent is to provide a drainage plane for water that seeps through the wall. I sealed the upper edges and sides of the dimple mat, but left the lower part open for drainage. I used DMX 1-step as the dimple mat in some areas, since it works well, it's durable, and it's thinner than the usual dimple mats you see used for drainage on the exterior of the wall, which saves some space.
It's better to waterproof the walls from the exterior, but if you're stuck and don't have that option, dimple mats on the interior can work, just understand that's not ideal, and if you have significant amounts of water coming throug that wall, the water can demineralize the wall over time and weaken it in some cases.
Bill
Thanks, Bill. We can't do exterior work. Interior is the only way to go
Is there more to your wall assembly? Foam needs to be rated for fire exposure or covered with an approved material such as drywall. If you are only putting up 1/2" foam and a dimple mat, it probably doesn't matter what the order is, but if there is more to the assembly then it might matter.
it's going behind studs and drywall
TooddadNJ,
Just a heads-up. 1/2" thick foam won't be enough. You need R-10 climate zone #4.
yup. we did 2"