“Rethinking Window Flashing,” by Harrison McCampbell (NOV/15)
Duane Oglesby (online, 10/28/15): The method used by the author is close to the AAMA 2400-02 standard. In coastal climates where there is a lot of wind-driven rain, we use “Method B” with a beveled sill. We also use custom stainless steel sill pans for our windows, and threshold pans on our doors. We strengthen our corners with FortiFiber’s corner shield, too. This is pretty much common sense, but I see all the time that contractors or installers just never get the proper training.
We stay away from certain housewraps, too, that just don’t work in coastal climates. Some plastic housewraps get destroyed by the tannic acid that leaches from wet cedar or redwood shingles and siding. We use BlueSkin and FortiFlash for most of our projects.
You need to pay attention to certain caulks, too, because they may be incompatible with the housewrap or flashing and may melt the membrane. This is why we always use the manufacturer’s recommended brands.
It all comes down to one thing: Do it right the first time using either a known standard or the manufacturer’s recommendation. Usually the standard will be better than the manufacturer’s recommendation, as the author stated in his article.
Editor’s note: For more on AAMA “Method A” and “Method B” window flashing, see Gene Summy’s article, “Installing Residential Flanged Windows: Two Strategies Compared”.
“Installing High-Performance Windows,” by Steve Baczek (Oct/15)
Matt Capitolo (online, 11/5/15): While I enjoyed reading this well-documented article, and appreciated the great lengths to which the designer went to create a weathertight seal, I was a bit concerned with how he designed the sill. The sill flashing details on this project consisted of a single membrane under the window that did not appear to turn or bend up 90 degrees. This means that moisture that might make its way in under the window would have an unobstructed path to the inside.
It’s also important to ensure that there is a clear path to allow any moisture that this sill might catch to escape. While the designer did include a sloped sill underneath the membrane, which should help, the real problem I had with this installation was a second membrane that appeared to act as a seal between the face frame of the window and the sill flashing membrane. This seemed less than desirable because it means that once the adhesive on the membrane fails, it might actually start to catch water and redirect it toward the exposed interior side of the sill.
While this design may hold up for a long time, it seems like it would have been much more sound to simply install a dam on the inside of the window pocket, flash the pocket from the top of the dam to the outside of the sill with a membrane, and then set the window in the sill on the outside of the dam. This would make the second flashing tape obsolete from a waterproofing standpoint. If one wanted to air-seal it, one could do so and it wouldn’t undermine the sill.
Steve Baczek responds: First, let me say thank you for your in-depth interest and your very good analysis of the window-installation article. While in some instances, I may choose to align with your thoughts, in this specific case, I stand by our decisions. Let me explain how we got where we did.
When you’re installing windows, the first fork in the road is to establish your approach to the window install—a water-managed system (as you suggest) a face-sealed system. If the decision is to develop a water-managed system, then your outline of a window install makes perfect sense, and I would align with your thoughts. However, because the house these windows were being installed in is a Passive House (with an airtightness target of .60 ACH 50Pa), we developed a “face-sealed system”—a barrier system designed to combat both water infiltration air infiltration, aiming for zero-tolerance for failure on both fronts.
The components that specifically keep water at bay include the continuous cleat, which the windows bear on, the sloping front edge of the opening, and the tape closure around the exterior perimeter.
If we installed the window in a “pan” as you suggest, we couldn’t have any holes to drain the water out. Keep in mind the .60 airtightness spec doesn’t allow for much air leakage. If water did get in, I am not sure I want it puddling under my finished sill.
Instead of using the interior dam you suggest, we chose to install the window on a cleat that was a bit higher than the sloping exterior sill. This provides the “dam” action you speak of; it just does it under the window. The flashing and tape we used on the project is the very best available today. Once installed, and installed properly, it does not release. While I can’t provide you evidence of a 200-year-old successful tape, I am willing to bet on these.
Based on my experience working on window installations with some of the nation’s top manufacturers and their engineering staffs, I know that when a window fails, it is most likely a head-flashing issue. On rare occasions, it is a sill failure, but usually at a sill with no pan and no slope (or a negative slope). Understanding that the head is a critical issue becomes a key design point for me; the most important goal is to ensure the window head does not see any water. On this particular home, the windows are placed in a 14-inch-thick double-wall assembly. This allowed me to slide the window in 6 inches to protect the window head—a luxury afforded by a superinsulated home.
Also, because these windows are installed in a wall system with very little energy to dry the system out, keeping water out becomes an even greater imperative. I typically water-test all the window installations prior to insulation. This allows us to find any inadequacies and make the necessary corrections.
“Common Siding Failures,” by Mark Parlee (Oct/15)
rcgrimsh (online, 10/25/15): I frequently look at siding problems, but am not always sure who manufactured the siding I’m looking at. Do you have any suggestions for distinguishing between the different brands of fiber-cement siding?
Mark Parlee responds: Thanks for reading the article and the comments. Sometimes, the siding is identified on the back side. We generally know who the builder was on the job, so a phone call can go a long way toward making a positive identification on the products used on the home.
The installation details are similar for all fiber-cement siding, regardless of brand. The big ones are: Do not overdrive the fasteners, and provide clearance at rooflines and at grade (although the clearance distance can differ slightly by brand). Generally failures of the products are due to installation details that are being followed, rather than to actual material differences.