Walls that can drain and dry last a lot longer than walls that stay wet. An air gap between the siding and sheathing lets both dry independently.
Furring strips are one way to make that air gap. Let's start at the beginning: It is smart to flash the bottom of the wall—to push water away from the foundation—especially if you insulate the foundation.
Step by step:
- Install housewrap, overlapping the flashing and then tape some bug screen along the bottom, wide enough to wrap over the furring strips.
- After windows are installed and flashed, install furring strips, screwing them into studs. Cut the furring short to make room for a mesh mat, like ridge vent along the bottom and top of the wall and windows.
- Fold the screen up and install a water table trim board just above the flashing. That way any rain that sneaks back there can drain out.
- Install a started strip for siding, and then finish siding the wall as you normally would.
Now, water can drain down and air can flow up at the bottom of the wall and the top of the window. The bottom of the window lets air escape behind the notched trim board, just like the top of the wall.
Walls that dry are walls that last for a long, long, time.
Synergy Construction via Building Science Corp
More to Explore:
Building Science Corporation:
- Ventilated Wall Claddings: Review, Field Performance, and Hygrothermal Modeling
- Modeled and Measured Drainage, Storage and Drying Behind Cladding Systems
- IRC FAQ: Cladding Attachment Over Insulating Sheathing
Hammer & Hand best Practices manual: