My back concrete patio cracked and sank a couple inches, so I am going to replace it with a paver patio. Now that the old patio sank, I can see that it was poured up against the house higher than the foundation. The gap that now exists between the siding and the old patio reveals the sole plate board for the back wall of my home. Do I need to drop the new patio down a couple of inches so that it buts against the foundation rather than the exterior wall of the house? Or can I safely protect the sole plate and wall by putting in some flashing or other barrier material?

Flashing or a length of pressure treated lumber to act as a buffer is all you need. I am not sure if you really can see the top of your foundation or not. Most siding jobs cover the top of the foundation with at least halkf of the first lap. Just do not start your new pation touching the house , that would hold moisture and maybe cause rot.

My back concrete patio cracked and sank a couple inches ///// The gap that now exists between the siding and the old patio reveals the sole plate board for the back wall of my home. Do I need to drop the new patio down a couple of inches so that it buts against the foundation rather than the exterior wall of the house? Or can I safely protect the sole plate and wall by putting in some flashing or other barrier material?

Why did it sink?

I would drop it. If any water sits in that gap and doesn't drain then wood rot. Flashing needs to drain somewhere to work right.

I agree with balg1 I think and hope you are looking at the house sheeting ply. Either or drop pad for getting water away from wood of house.

Bal 1 It may be the joist band/plate. Ive sen where the OSB was cut out and crete was directly against the wood. BAD building. When I run into that I either drop slab or if grade won't allow I tar that spot. Flash over that and silicone edges, and then butt crete

Helprich get back on what you actually see

You will never go wrong use block/concrete/brick wall to butt the concrete floor.

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