Wall assemblies that incorporate rigid foam insulation over exterior sheathing, followed by furring strips and siding, are becoming common. The extra layer of insulation helps reduce thermal bridging through wood framing, and the furring strips create a ventilation space behind the siding that promotes drying.
But writing in a Q&A post at Green Building Advisor, Sonny Chatum wonders whether this wall system, often called a “vented rainscreen,” is compatible with vinyl siding.
“I am referring to a general wall assembly with several inches of rigid foam over studs, followed by 1-by or ripped 3/4-in. plywood furring strips attached with HeadLOK screws into studs, say on 16 in. centers — so that there are voids, or vented, areas between strips,” Chatum says. “How does the siding installation hold up if installed over such strips? Is it good to make the strips wider than, say, 4 inches so the vented areas are less and support for the vinyl is more? CertainTeed vinyl siding installation instructions seem to be against this vented approach, but at the same time their website points to a technical bulletin from FastenMaster that certainly supports the furring strip approach — so they are confusing.”
It’s an intriguing question that could potentially affect many builders and homeowners. Is it OK or not?
Industry group seems to back idea
Several posts direct Chatum to online articles about the correct way of attaching furring strips to the wall over a layer of foam, but it is the vinyl siding itself rather than the furring strips that has Chatum concerned.
Specifically, he wonders whether the void behind the siding between the furring “presents a problem for the lasting integrity of a vinyl siding installation.”
On this question, GBA senior editor Martin Holladay offers a link to a Vinyl Siding Institute installation guide that…