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Green Building Blog

The Complicated Role of a Water-Resistive Barrier

Choose the right product and install it well, because if you’re not keeping water out, nothing else matters

A water-resistive barrier is only as good as its installation. The right type of fasteners, the required overlap of seams, and other installation details provided by the manufacturers must be followed to satisfy the building codes.

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.…

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3 Comments

  1. Malcolm Taylor | | #1

    A comprehensive and excellent overview.

    While I'm greatly indebted to Steve Baczek for the work he puts into thinking about these subjects, share his views on WRBs and building assemblies, I just can't go all the way down the path he suggests and think of open-cladding as a well-performing first layer of protection for ventilated wall cavities.

    By opening up the siding to bulk water intrusion you both put too much emphasis on the underlying WRB, and make the cavity work harder than it needs to. Detailing the cladding to stop the vast majority of water leaves a well-detailed WRB and flashing to perform the roles that Brian has catalogued so well in the article.

    To me the only legitimate reasons to use an open-cladding are aesthetic. In most climates that may be reason enough, but in marine-coastal ones I just don't see it.

  2. User avater GBA Editor
    Brian Pontolilo | | #2

    Hey Malcolm,

    I'm kind of a modernist, so I love the look of open-gap siding, but I share your hesitations and I'm not sure if I'd do it if I were building my own home.

    Steve's not the only one using it, of course. I've seen quite a few homes with that siding detail all across the country over the last decade or so. Steve's a smart and thoughtful architect though, so I've asked him to write something on the topic for GBA. More to come...

    1. Malcolm Taylor | | #3

      Always enjoy anything Steve contributes.

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