Zip installed, exterior insulation next question about a rain screen behind insulation.

A homeowner working on an older house is re-siding it: the old siding came off, new taped-and-sealed Zip sheathing (a structural panel with a built-in weather barrier) and windows are going in, and exterior foam insulation is next. The question was whether a rain screen, a ventilated gap that lets water drain and air dry out the wall, needs to go between the sheathing and the foam.

An expert building-science responder said no. A rain screen only works when it sits directly behind the cladding, the actual siding on the outside. Putting one under the foam wouldn't do its job there. He did note that Joe Lstiburek, a well-known building scientist, recommends using a dimpled house wrap between the sheathing and the exterior foam instead. That thin, bumpy wrap creates a small gap that gives the wall a drying path without functioning as a true rain screen.

For anyone doing a similar re-side-and-insulate project, the practical point is where the ventilated gap belongs: right behind the final siding, not buried under the foam layer. If a dimpled wrap or similar product goes between the sheathing and foam, it's there to help the wall dry out over time, not to drain bulk water, since that job is handled by whatever gap sits behind the actual siding.