After taking classes for the past 15 years, my sister graduated from college last week. While I was in Lakeland, Florida for her graduation, I took the photo above. It’s a hotel under construction. I took this picture because I was surprised to see curtains in the windows at this stage of construction. Oh, wait! Those aren’t curtains. That’s house wrap.
The telltale sign of improper window flashing
House wrap acts as a drainage plane. It’s the control layer for liquid water that gets behind the cladding. Its job is to drain the water all the way to the ground without letting it into building. Shouldn’t be so hard, right? Gravity pulls stuff down, so just let it do its job.
One of the main problem points is at openings, like windows and doors. The house wrap has to be flashed properly to keep the water moving down and out, not down and in. That means you want the upper layers to come down over the top of the lower layers. Where builders often get this wrong is at the top of a window.
In the photo above, I spotted the house wrap hanging down from the top of the window inside the building. That means they didn’t shingle the house wrap over the top of those windows. The house wrap runs behind the top of the windows. Here’s another photo showing the same improper flashing.
When you see house wrap wrapped around the window header on the inside of a building, it’s not done properly.
The official Tyvek window flashing instructions
In both of the photos above, the builders used DuPont’s Tyvek house wrap. (If I were going to use house wrap on a building, that’s what I’d use, too, because it handles water better than the perforated plastics, but that’s a different issue.) It shouldn’t be that hard to follow manufacturer’s instructions, but that doesn’t always happen.
Especially with the ease of looking things up online now, finding the proper methods for stuff like this is easy. If you go online and search for “DuPont Flashing Systems Installation Guidelines” or something similar, you’ll find their ten page pdf on how to do this properly. Here’s the diagram for step 1 in the window flashing process.
Notice the difference? The house wrap is pulled up on the exterior of the building at the top of the window. After some other steps, here’s what the step 4 diagram shows:
The window is installed. Next, flashing tape goes over the nailing fins at the jambs first and then the nailing fin at the header. Now we’re ready for step 5, below.
Now that flap of house wrap above the window comes down and gets taped off. Voilà! We’re done. Now the rain can drain down the plane, even when we’re not in Spain. (Now you may groan.)
Allison A. Bailes III, PhD is a speaker, writer, building science consultant, and the founder of Energy Vanguard in Decatur, Georgia. He has a doctorate in physics and writes the Energy Vanguard Blog. He is also writing a book on building science. You can follow him on Twitter at @EnergyVanguard.
Image credits: Photos by Energy Vanguard, window flashing diagrams from DuPont™ Flashing Systems Installation Guidelines.
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