As a teenager, I worked for a small general contracting company. In between a lot of grunt work and coffee runs, I learned to do some carpentry. On two jobs, I helped install siding. When we installed cedar shakes, the carpenters taught me to offset each seam as much as possible to keep water from getting behind the siding. When installing clapboards, we backed up all of the butt joints with flashing, which has long been best practice.
Fast forward 20 years: I’m working at Fine Homebuilding magazine, visiting the job site of a high-performance home that was designed by a well-respected architect and is being built by an experienced builder. On the coast, where wind-driven rain is a regular event, the crew had just finished installing the “open-gap,” or “rainscreen,” siding—that is, siding installed over furring strips with an intentional space left between the boards.
How did we get from laying a healthy bead of caulk where siding meets trim to leaving a wide open space between each course? When did we stop relying on siding to keep water out, and start installing it to let water out? Perhaps it was the mold explosion in homes at the turn of the century and the work of architects, building scientists, and educators like steve Baczek who showed us that even the best siding installation is no match for water, and that every house needs a dedicated and effective water-resistive barrier, or WRB.
“Mother nature has a perfect record,” said Baczek, “Water is the number one killer of buildings.” The International Code Council agrees. Section R703.1.1 of the International Residential Code (IRC) calls for a WRB behind siding and only allows exceptions for some masonry walls and wall assemblies that have been specifically tested to show resistance to wind-driven rain.…