I have a poured concrete porch that also serves as a roof for a basement storage room. When the builder proposed creating this space, I had reservations but he “did them all the time and they never leaked.” Even so, I asked the him to include a roofing membrane that would extend from the house wrap (spanning the joint between the slab and house) and under the slab out to its edge. I thought the sub had completed this step, but it’s now apparent that he did not. I now have a slow drip into the storage room whenever it rains.

Can someone provide a workable solution for sealing the joint that won’t involve ripping everything apart? The profile of my exterior wall system is 5/8 OSB, commercial house wrap, 1 inch blue foam, strapping, and then cement fiber siding. The joints on the OSB and foam are all taped. I think most of the leak is due to water hitting the siding and splashing down on to the concrete porch. The house is fairly contemporary so the porch is largely uncovered and there are minimal roof overhangs. Where the water is entering the house, there is a small bump out with a shed roof that drains on to the porch.

Ames Research has some interesting tapes and EPDM mastics that look like they might have potential for spanning and sealing the joint. Thoughts?