R-etro Leaves Some Gaps Unfilled
I was initially excited to read about the R-etro System, designed to make exterior insulation retrofit applications easier (see EBN). After reading the article and checking out the installation details on the manufacturer’s website, however, it looks to me as if the R-etro System addresses some of the easy problems about applying exterior rigid foam but none of the hard ones.
It’s not that difficult to figure out how to put rigid foam up on a flat wall. What is hard to figure out is what to do at the foundation, around window and door openings, at porch roofs, and at the eaves. The R-etro System does not make any of these tricky details easier. For instance, the suggested windowsill detail shown in the online installation manual seems outright risky, relying as it does on an exposed caulk joint at an inside corner. The suggested eave detail indicates that the exterior insulation is to be sealed to the underside of the soffit, which seems analogous to securing your dog’s leash to the leg of an aluminum beach chair.
Two other points: first, the product comes only in an R-18 thickness. This is thick enough to help prevent condensation in the wall cavity, as the article points out, but it may not be thick enough to yield the overall wall R-value needed to achieve a specific energy-savings target. If I’m going to go to the trouble of adding exterior foam, I want to be sure I’m adding what my calculations tell me I need, not what a manufacturer chooses to provide. Second, Douglas Bennion of Quad-Lock says no air gets behind the panels, and John Straube advises that a good air barrier still needs to be applied under the product. It seems to me, however, that given the number of joints in the product (these are 1' x 4' panels, after all, not 4' x 8' sheets), and given the difficulties that jobsite realities often impose on fully meeting manufacturers’ expectations, one would want to add an air barrier outside the R-etro System to minimize air movement between and behind the panels.
Despite my complaints, I am very glad that Quad-Lock Building Systems is trying to address the challenges of exterior insulation retrofits. I hope, however, that they don’t stop with the R-etro System and that they go on to develop products that really do make exterior retrofits easier, and not just appear to make them easier.
Paul Eldrenkamp, Owner
The Editors respond:
Your points are well taken. Builders who choose the R-etro system are not home free—they still need to develop proper water management and thermal envelope details to ensure a durable installation that performs well. Of course, builders who want to add more than R-18 to existing walls will probably choose a different approach. But R-18 foam is still more than most siding contractors are currently installing. It’s up to the builder to determine air-barrier details for any wall. Your recommendation for installing an air barrier on the outside of R-etro System foam certainly can’t hurt, since redundant air barriers usually improve wall performance.
Published July 30, 2009