Fastener Choices for Installing Wood Furring Over Continuous Exterior Insulation – GreenBuildingAdvisor

By Randy Williams | February 14, 2025

We install vented rainscreens on buildings to promote drainage and drying, between the wall sheathing/water resistive barrier (WRB) and the siding. There’s some debate on the optimal gap size of the rainscreen, but 3/8 in. (about 10mm) is what many building scientists recommend. Often the material used to create this gap is strips of plywood, wood lath, or a plastic product (such as Cor-A-Vent). When this furring is being installed right over the sheathing and WRB, it can easily be nailed or screwed into framing. When combining a vented rainscreen with continuous exterior insulation (CEI) we may need a more rigid material to create the gap, because it is not only there to create the rainscreen gap but also to hold the CEI on the wall. And it’s the fastening point for whatever siding or cladding you are using. In this case, many builders choose a structural screw for fastening.

This is where things can get tricky. Depending on the thickness and density of the exterior insulation you’re using, there may be challenges in maintaining flatness across the wall. Attaching a 1x product through thick layers of insulation can result in “ins and outs” that require adjusting. Some insulation products are more susceptible to this condition than others; rigid mineral wool insulation, which I used on a recent project, is a good example. With some trial and error, I’ve settled on a fastening system and procedure that works well. I’ll share that here.

Fasteners for rainscreen furring strips: What the code says

What are our fastener options for securing 1x boards…