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Interior drainage mat (waffle board) alternative

I am currently retrofiting an interior drain tile in my basement and insulating with rigid foam. The front half of my house is 6' below grade and the rear is 6" above grade. I have installed waffle board against the interior side of the block foundation walls, where we are below grade, to direct any water that makes its way to the interior, into the drain tile. It wraps the entire perimeter and terminates 2' above the slab (3' wide roll). However, I have found that this waffle board/drainage mat material is very expensive! All of the details that I have seen on your website show the waffle board running all the way up the entire foundation wall (7' in my case). Since my budget will not allow that I was wondering if it would be possible to use the the leftover Tyvek Drain Wrap I have from our exterior work. So the DrainWrap would go against the block wall and tuck behind the waffle board that extends 2' out of the slab. My rigid insulation would then be installed against the drain wrap. Any reason why this would not be ok? I am insulating the walls with recycled poly-iso and thought this might be a good way to keep any water that comes in from ever making contact with the insulation while providing a path to the drain tile and keeping the budget in tact.

Thanks for any feedback in advance.

Asked by Charles Chiampou
Posted Jun 10, 2014 11:12 AM ET

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3 Answers

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1.

There is little value to installing an interior side drain plane on the interior side of foundations- only if you anticipate flooding events is it really worthwhile. Even fiber or asphalted facers on polyiso provide at least some capillary break between the CMU & foam, and it's nearly impossible to build it without at least some minimal air gap due to the mortar joints and not perfectly co-planar aspects of CMU construction. Most of the foam will have at least a micro-gap. Installing leftover Drain Wrap won't hurt, but probably isn't necessary.

Answered by Dana Dorsett
Posted Jun 10, 2014 11:38 AM ET

2.

Great. Thanks Dana.
Do you have a tape you recommend for polyiso with fiber facing?

Answered by Charles Chiampou
Posted Jun 11, 2014 11:30 AM ET

3.

There are no purpose specific tapes for that use. Some facers stick pretty well to housewrap tapes.

But fiber-reinforced duct-mastic applied with a trowel or paint brush at ~1/8" thickness sticks to every thing. Spread it an inch or so each side of the seam.

Answered by Dana Dorsett
Posted Jun 11, 2014 2:08 PM ET

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