Wrb detail options for zone 6

A homeowner building a new house in northwest Montana asked a building forum for budget-friendly ways to handle the water-resistive barrier (WRB, the wrap that keeps water out of the wall) and rain screen behind metal siding on a 2x6 wall with fiberglass insulation and no exterior foam board. With metal siding and no outside insulation layer, some moisture can build up against the wall, so a gap for drainage and airflow behind the siding matters.

Responders suggested several ways to create that gap without spending much. Options include drainage mesh products, but those cost more and mainly save labor on bigger jobs. Cheaper do-it-yourself alternatives include ripped strips of corrugated plastic sheeting, plain wood furring strips (ideally with a tapered top edge), or horizontal strips of a vented product called Cor-a-Vent spaced about every 32 inches. If using a mesh or dimpled wrap instead of strips, a perforated flashing at the bottom of the siding helps air move through the gap. For the WRB itself, a full self-adhered membrane (like Henry Blueskin) only makes sense if it's also doing the job of sealing air leaks; otherwise a heavy-duty version of house wrap, such as Tyvek Commercial, is a cheaper option that still lets moisture escape from the wall.

For homeowners planning their own upgrades or new builds, this points to a broader lesson: metal siding without exterior foam usually needs some kind of drainage gap behind it, and there are inexpensive ways to build that gap without buying premium wrap products.