Renovating a largish split level ranch. The house needs new siding and the existing 2 x 4 frame walls are filled with fiberglass batts. there are 2 issues I am facing in addition to creating more R value-> 1 - The windows have all been replaced with Andersen 400 series but the house was foreclosed (2 years ago) before the house wrap was repaired and siding replaced. I'm planning new Boral plank siding butted to the windows with no casing and mitered joints at the corners of the walls. The plywood has not responded well to the exposure and the sheathing ends at the top of the subfloor. This creates minor surface irregularities that could be evened out by adding 1/2" foam insulation board on top of the sheating. Where would you put the house wrap in this case? I assume new flashing tape at all doors and windows and caulk the new siding butts at the sides and tops of all openings. I like the look of the narrow jambs without casings. 2 - In the interest of more insulation I am considering 2" of foam board on the interior of the house. Currently there is oil fired radiant baseboard at all exterior wall and I really dislike the look of those metal covers intruding into the rooms. My design would be to add the insulation on top of the existing sheetrock down to the top of the BB heaters with new 1/2" rock and appropriate closure over the BB to have a flush wall surface. The BB heaters would remain in place. Any thoughts? Thanks in advance for all input. Robb

Half inch exterior foam under the siding isn't sufficient for dew point control at the sheathing for US climate zones colder than US climate zone 4A/B, but if it's polyisocyanruate it would squeak by in US climate zone 4C. If adding 2" of interior side foam there's the additional potential for creating a moisture trap.

So, where is this house located?

The housewrap can go on either side of the exterior foam, as long as it's lapped properly with the window flashing.

The house is in the Hudson Valley - Hyde Park, NY. moisture trap is exactly my concern... What would you advise? I am also considering a rain screen approach on the outside but I am limited to 1/2" because of how I plan on detailing the windows at the siding.