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Question DetailsAsked on 5/3/2016

How do I stop Rain water from coming down the inside of the house wrap thru top of basement windows.

Four windows above the deck. Four windows below the deck. Basement is not finished yet. Rain water comes down the inside of the house wrap and leak into the top of the basement windows. I have caulked the around all eight windows with silicone caulking. I have caulked around the bolts on the outside. There is small space between the deck and the house. This space is so small I cannot determine if this where the water is coming in through the bolts. This need to be fixed before the basement walls are insulated and sealed. The exterior of the house is brick.

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Since you have caulked all the windows with no effect, and assuming your siding is not the problem, I would be looking at the space behind the deck. No telling if the small space left there was for drainage and there is proper drainage membrane and flashing there, or if it was built tight to the house (possibly after removing a strip of bricks ?) so you may have a full gap there where the rainwater is going down between the house and deck, and then right in behind the bricks (assuming this is brick facade).

You don't say how large or high the deck is but if windows below it presumably 5-6 feet off ground, so probably not too easy to partly dismantle it to see how it was built and if there is flashing there.

You could try putting proper flashing at the deck surface to keep water from shedding down into the gap, then flashing at the underside of the deck to try to trap any water going down the wall, but without removing the deck ledger board (meaning disassembling the deck) that would be a very iffy thing on the bottom side and likely not possible to do fully correctly at the top either. It might be that double-layer topside flashing set into the brick would work. The bottom flashing would go under the deck boards (so have to tear up ones nearest the house - pretty easy if deck boards parallel the house, not so much if diagonal or end-butted into the house. The top flashing would then overlay the top board - commonly a narrow board liek a 2x2 so the flashing can stick out just a couple of inches from the house but still reach the first board gap. Of course, with diagonal or end-butted boards this one just ends up on top of the boards, so while it can be caulked down under it does not really "waterproof" that joint. The first deck board by the house should also be sloped away from the house - commonly done by setting the joists a hair low on the ledger board, so the edge/ends of the boards at the house contact slope outwards to drain. And that/those boards should never touch the house - leave 1/4" air gap to prevent wet deck boards from wetting the house face.

Here are a couple of links to graphics showing typical deck / house interface waterproofing -

Since the gap is too small to see into (presumably too small for a fiber optic scope too - about 3/8-1/2" opening needed for that ?), you could investigate (when leaking in) by knocking a few small holes in the drywall on the inside and see where it is and is not wet - like say a foot or two above deck level to see if coming from above there or not (meaning upper window or siding leaks), then basement ceiling to see if coming in on top of and through the plywood sheathing forming the first floor, at the top of the rim joist, at bottom of rim joist, and whether it is coming down the inside of the rim joist till it hits the top of the downstairs windows. This would also give you a chance to see if you are looking at decay of the wood in the walls and flooring from this prolonged wetting.

Obviously, if the water comes in at ALL or most of the downstairs windows then it is due to a systemic waterproofing failure, not just at one point.

Answered 4 years ago by LCD

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