Aaron Vander Meulen is building a house whose exterior walls will consist of 2×4 framing with cellulose insulation, bracing, 2 in. of extruded polystyrene (XPS) foam, furring strips and, finally, Extira siding, an exterior grade wood composite.
Meulen is leaning toward horizontal rather than vertical furring strips because they’ll make it easier to install the 2-ft. by 4 ft. panels.
“Running the furring strips horizontally allows the panels to be fastened in a location the makes sense for the panels, as well as allowing some customization of panel size,” he writes in a Q&A post at GreenBuildingAdvisor. “What am I missing/overlooking?”
Horizontal furring is a problem
Installing the furring horizontally might make it easier to put up the siding, but it will to cut down on the flow of air behind the siding and will block the drainage of any water that gets past the siding.
Torsten Hansen suggests offsetting the furring away from the foam to allow back-venting of the panels. But William Geary suggests even this won’t be enough.
“The horizontal furring strips are the problem if you don’t provide for (1) sufficient drainage for the rainscreen (this will be blocked by the horizontal strips), and (2) sufficient vertical airflow behind the siding (this also will be blocked by the horizontal furring strips,” Geary writes. “I doubt you can cut enough kerfs to provide for adequate drainage AND airflow.”
Instead, Geary suggests one of three options:
“Whatever you do, make sure…