I don’t think I can ever say it enough, but the building enclosure consists of several control layers and each one has its job. The primary control layer is the one that keeps liquid water out, and it can be a tricky business. Take the case of this condo building (yes, it’s in the community where I live). It’s got several problems, so I went to bat for building science here.
We’re having a couple of porticos built, and one day I noticed one of them in the stage of construction you see above. These buildings have no overhang, so that wall will get wet. The contractor put house wrap on the wall and then built the portico. The felt on the roof, as you can see, goes up the wall a bit, but on the outside of the house wrap. Problem?
Yes, that’s a problem. Any water coming down on the outside of the house wrap can go right down behind the felt and rot out the framing of that portico. Did I mention the building has no overhang?
I saw that I had still had a chance to help get it done right, so I talked with the president of the homeowners’ association and told him we need to make the contractor do it correctly. The house wrap needs to come down over the roof underlayment.
Also, since they hadn’t yet cut the house wrap for the window, I printed out the instructions on how to do that, too. Unfortunately, I wasn’t able to talk to the contractor directly at that point, so here’s what it looked like after a few days:
They did the standard window cut for the house wrap — a big X — then put the window on top of the house wrap and put flashing tape all the way around, on top of the house wrap. If no water ever gets behind the house wrap, this might be OK. On this building, with no overhang, it’s quite possible that water can get behind the house wrap. The tape on top of the house wrap wouldn’t help, and the window framing could rot.
They also didn’t fix the flashing detail at the roof. Notice they installed step flashing — but put it on top of the felt, which is still on top of the house wrap. Ugh!
Finally, we arranged a meeting with the contractor that I could attend, and we got things straightened out. Here’s what they corrected:
- We got them to replace the house wrap with a vapor permeable material, not just perforated plastic. (See Matt Risinger’s article and video about this. I’ll write more about it in a future article, too.)
- The house wrap now comes down over the flashing at the roof intersection.
- The house wrap comes down over the top piece of window flashing tape.
It’s not perfect. They should have kept those nails at the roof intersection above the step flashing that runs beneath the house wrap. But it’s far, far better than we got initially.
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.
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