“Working With Thick Layers of Exterior Foam,” by Clayton DeKorne (May/15)
Bob Dorazio: Instead of sheathing corners (only) and then furring with thin foam, we used another way to achieve an in-plane wall surface before sheathing with foam. We used to take OSB scraps and rip them on a table saw to 1 1/2 inches or so and fur the unsheathed studs so they were flush with the sheathing. This approach seemed to pencil out at a lower cost compared with sheathing the entire house. These days, though, sheathing the entire house is more common.
“Weather Barrier Update: Good, Better, and Best,” By Matt Risinger (May/15)
Robin McC (online, 5/11/15): I know companies test products to simulate 50 years, but I have a hard time believing that tape I apply to anything today will still be adhered in 50 years. That doesn’t mean I don’t use new products, it just means I don’t think we have found any holy grails.
David Landry (online, 5/11/15): I am a little concerned about your comments regarding the UT [University of Texas] testing of the thinner liquid-applied WRBs. These products, such as Sto-Guard and Prosoco Cat-5, are not designed for UV exposure for longer than six months, and I would expect them to be degraded after nearly two years in the Texas sun. Product longevity should be evaluated according to the designed specs. No?
Matt Risinger responds: I agree that UV damage is a major issue for these WRBs and that this “torture” test isn’t necessarily an indicator for performance. I am merely suggesting that we evaluate critically the waterproofing products we use, as they can’t easily be inspected and they need to last for decades or even generations without failure.
Mr. Common Sense (online, 5/10/15): We just re-sided a 60-year-old house that had 1x8 sub-sheathing covered with 30-pound tar paper and no water damage found. How far we have come!
Conrad vonBlankenburg (online, 5/13/15): I am always amused by the “newest” product! Any of us who have worked on older buildings (1800s) know that the primary barrier does not need a secondary barrier. All of the buildings from the 1890s I have worked on had redwood shiplap siding nailed directly to the studs. They had very little decay unless some bonehead had piled soil against the wall. Window sills lapped over the siding with a rabbet on the bottom. The carpenter borrowed methods from boat builders to prevent rain from entering the building. I have always used two layers of 15-lb. felt under siding or stucco for the primary barrier, on thousands of buildings. This helps keep wind-driven rain from finding its way into the structure. Attempting to seal the building from air circulation is a fool’s errand. The large accumulation of moisture “inside” the living space has to get out or the building will rot.
Matt Risinger responds: In response to Conrad and Mr. Common Sense: I agree that tar paper has worked well for generations. But remember that those older homes tend to have solid lumber sheathing, full 2x4 studs, and no insulation. They can “leak” without causing problems. Newer homes tend to be much more moisture sensitive and have very little capacity to “leak” without failures occurring. Thanks for reading and commenting.
“Installing Drywall Over Rigid Foam,” by MYRON FERGUSON (oct/12)
Mark Attard (online, 5/31/15): I would caution against installing rigid foam on the inside of a building without first assessing the rest of the roof assembly and considering the climate zone. Applying foam on the inside of a building does not address the issue of thermal bridging. Because roof joists offer little in the way of thermal resistance, cold air will penetrate into your insulation cavity. Once it hits the warm air of the cavity, it will condense. With no way for the moisture to escape, you are setting yourself up for a disaster of mold and rot.
Pete Goldie (online, 5/31/15): I, too, strongly recommend looking at the possibility of condensation forming between the rigid insulation on the roof sheathing. In my own house, I never had a moisture problem in the attic. But adding 3 inches of poly-iso suddenly made the north-faced roof saturated enough to drip through cracks and joints. Fortunately, I had not installed the drywall yet, so I removed the rigid, added six eyebrow roof vents, and furred out the rigid to provide circulation between the sheathing and insulation. This happened in the mild climate of San Francisco. By the way, the south-facing side remained dry as a bone.
