This link is to a picture of the part of my home exterior needing repair: home repair pic I think this is not a hard repair. I just need to be sure I do it right. First of all, the black sheathing had some damage and has been removed. So, what shows now are the studs and the insulation. I need to know the right way to close this in before putting on the siding. I plan to buy a sheet of exterior sheathing the same thickness as the old black sheathing and nail it on.

My questions :
– Do I need to put plastic over the studs and insulation first to act as a vapor barrier, and if so what kind of plastic?
– Where the new sheathing and the old sheathing meet do I need to seal that crack in some way? Caulking? If so, what kind of caulking?
– Do I caulk all around the new sheathing? If so, what kind of caulking?
-Is it ok if the new wood sheathing touches the cement?
Please note that the rotted sill has been replaced.

My first question would be, is that sill plate in the picture rotted? if so this is a more involved repair if you are going to do it right.

Yes, the sill was rotted. When I bought the house there was a planter in that location, approx. 10′ long and 2.5′ deep. It was very sturdy and well built except that it had no back. It was just three sides, and between all the wet dirt and the house was just a layer of tin and a layer of cement board. I did not know this until during the winter the whole thing tipped forward away from the house. So, I removed the planter figuring that the wall and sill might be rotted. Only the sill was rotted. I replaced the rotted section with treated lumber, and secured it in place with long anchors that go through the wood and deep into the cement. Now I just need to close up the wall the right way.

No you do not want to put plastic on the outside of the insulation that goes on the conditioned side of the insulation. You nee to cut the sheathing to fit the openings fairly closely. You probably wouldn’t need to chaulk the joint between the two You could if you are concerned about insect or wind infiltration. Putting Tyvek or tar paper over the sheathing would be a good idea. The current sheathing that you removed is, I think, a OSB coated with a sealant to make it more weather resistant. Tuck the Tyvek up under the siding above and out under on each side. Put on new siding. That should have you covered.