More Q&A Spotlight
The exterior of a house is a collection of very functional materials. The primary job of roofing, windows and doors, and siding is to protect the interior of the home—to keep nature from getting all over the couch, among other things. Although these materials were once limited to a few that were available locally, today there’s a huge variety of products available for each of these functions, and a supply chain that means you can pick and choose materials that not only protect but also add style to your home. Siding, in particular, comes in various materials (brick, stone, wood, composites, PVC) and looks (clapboards, shakes, nickel-gap, board-and-batten), and over the last 50 years, with advances in materials and techniques such as rainscreen assemblies, it has become better at its job. But for the most part, designers and builders count on siding to be the first layer of defense against bulk water—except when they choose an open-joint system.
Open-joint siding is just what it sounds like: siding—often 1x material installed over battens—that is installed with a gap between each piece. Open-joint siding can be installed horizontally or vertically. One theory is that the gaps allow any water that gets behind the siding and would otherwise need to drain to the bottom of the wall or dry via convection an easier way out. Critics point out the obvious: open joints guarantee that water, critters, UV light, and the like have easy access to the WRB, flashing details, and penetrations. But lots of people like the look, including GBA member “Arkhouse.”
Considering open-joint siding in Canada
In a recent post in our Q&A forum, Arkhouse writes that they are building a home in Ottawa, Ontario, and that they like the idea of open-joint vertical siding. However, they are…
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7 Comments
I am interested in hearing more about Steven's thoughts on the reverse board-and-batten system. That's one of my go-tos for affordable, natural, attractive siding, with a built-in rainscreen. I do put a drainage membrane behind the battens so the boards aren't sitting tight to the WRB. The battens can dry readily to each side and the exposed portion of the face (usually 3/4" in my case) can dry directly to the exterior. But I don't have more than a few years of in situ performance to assess exactly how long the system will last.
Do you attach the cladding with fasteners through the battens, WRB and sheathing at the very edge of the cladding?
Unfortunately Steve isn't a disinterested expert on this topic, he is a proponent for open-cladding.
"I understand people’s concerns, but my preference is to trust the science". If you are going to say your approach is based on science, (and by implication others somehow isn't) you need to cite the science you are relying on.
"we recently finished one of the most expensive cladding systems we ever have done... It worked perfectly. Like its predecessors, it has no rot, no bugs, no mold." These are problems that occur over time. Finishing up an exterior and saying it works well I don't think is very useful commentary. And the problem isn't primarily with what occurs outside the WRB, it's whether the cladding and WRB is adequately protecting the wall behind.
"While I didn’t do it on my recent project, testing experience on other projects would suggest that if I sprayed water on the joint, it would catch the edge of the board and ride it to the bottom. I do not think a lot of water is actually making it back to the UV membrane." That's not what the science I have seen is. RDH shows these open cladding let an awful lot of water through to the WRB: https://www.rdh.com/wp-content/uploads/2017/10/RDH-BSL-Drainage-Balance-Spray-Rack-Report.pdf
I haven't been able to find any hard data on it, but open joint cladding is also seemingly a massive compromise in terms of fire resistance.
Increased surface area, increased airflow, ability to trap embers, ability for the flames to get past the siding before having to burn through it, basically everything you don't want in a fire resistant design. It could be mitigated with noncombustible siding and or underlayment (gypsum, mineral wool, fire rated sheathing, etc.) but of course that increases the cost and upfront emissions.
While many people may not be in a high fire risk area now, its anyone's guess what that risk, or insurance companies' tolerance for such an assembly, will be over the lifetime of a well built structure.
bcade,
Good point. That's something I had never considered.
I really appreciated Steve's response here - but I didn't understand this part of his point - why is vertical better? Is he saying that it drains better and thus the wood will last longer?
"While I have done open-joint claddings in a horizontal orientation, my preference is the vertical orientation. Here’s why: With 3/4-in.-thick boards and a 3/16-in. gap, the space between ends up relatively deep and narrow. While I didn’t do it on my recent project, testing experience on other projects would suggest that if I sprayed water on the joint, it would catch the edge of the board and ride it to the bottom. I do not think a lot of water is actually making it back to the UV membrane. If it does, who cares?"
Correct me if I'm wrong, but this appears to be an example of one of Steve Baczek's projects using the open joint siding technique he described:
https://stevenbaczekarchitect.com/info/newburyport-massachusetts-home/
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