In the last residing, the old wood siding was covered with green foam board as the water-resistive barrier and the new vinyl siding was install on top it. I know it was not a good practice in general, but it was long time ago and I had no control.

One problem I find other than that is there are gaps between the foam board, and I think water can get in. The wall meets a concrete slab at its foot, and there’s a piece of flashing there. Once water gets into, there seems no escape. My question is how to seal the gap properly. It seems the right way is to seal the gap all the way up to the top of the wall, but it requires to remove all the sidings. Is there an easier way to do it?

The gray thing in the gap is some caulking, but I don’t think it will stop the water from getting behind the foam. enter image description here

  • You don't seal the bottom that's where any water that's managed to get in is allowed to escape.
    – FreeMan
    Commented Dec 15, 2023 at 13:17
  • @FreeMan If I don't seal the bottom, the water from the slab goes into the wall. If I use a flat flashing against the wall instead, the water goes into the gap between the slab and the wall, causes settlement of the slab, and will eventally lead to standing water against the wall after settlement.
    – bobby_yan
    Commented Dec 17, 2023 at 16:16


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