Down and Out Is the Rule for Draining the Rain

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window-flashing-moisture-management-house-wrap.jpg

I'm seeing more and more projects with house wrap where the installers do the window details properly. Or at least better. The photo below shows the house wrap lapping over the flashing tape at the top of the window. Often it's the reverse. And the house wrap in those cases is not only beneath the flashing tape, but it's also beneath the window's nailing fin.

 

So they did that detail pretty well here. Water that gets behind the cladding will run down the house wrap and not be channeled down into the framing if the tape fails or wasn't installed well. Likewise, water that gets behind the house wrap should be stopped by the tape, unless it fails.

But let's step back and take a look at the bigger picture for this house. The photo below shows that same window — and what's above it.

The first thing to note is that we have a design failure. There's a window right below that roof section. And there's also this thing called gravity, which still likes to pull things downward. Water hitting that roof could lead to failure at that window or on the wall unless all the details are done properly — and maintained.

window-flashing-moisture-management-house-wrap-design.jpg

See any potential problems at that roof wall intersection? Let's zoom in.

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Hmmm. The house wrap runs down behind the step flashing. They made the mistake here that they avoided at the window header. Water that gets behind the cladding can get channeled down behind the step flashing. That's almost a certainty for water that gets behind the house wrap. (Here's a nice article on Fine Homebuilding's website showing how to install step flashing.)

In addition, there's no flashing behind the house wrap right below the bottom course of step flashing. Even if they came back and put tape all over that area, it's in the wrong place. Water could be coming down behind the tape.

Here's what the house looks like now that it's finished.

window-flashing-moisture-management-no-kickout-flashing.jpg

It may be a little hard to see in this photo, but there's no kickout flashing here. That's another detail that can help keep the water away from that wall as it comes down the roof when it's raining. (Here's a nice article on Fine Homebuilding's website showing how to install kickout flashing.)

I've written a lot about the importance of being a building enclosure control freak. Controlling the flows of heat, air, and moisture (both liquid and vapor) is critical to achieving comfort, healthfulness, durability, and energy efficiency. Of the four things to control, though, liquid water is the most important. It can cause a building to fail more quickly than any of the others.

Unfortunately, a lot of builders are still putting houses like this on the market. The kinds of problems I found in the one described here aren't rare. And home buyers who see only the final product have no way to know that there's a ticking time bomb built into their new home.

 

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Comments

Rich Lavoie

I learned this lesson the hard way on my own home! The lack of a "kick-out" flashing and general poor workmanship by the builder where that lower roof meets the siding caused rotting of the thirsty OSB sheathing and Masonite clapboards all the way down to the sill. Not to mention the ant infestation that this lead to. Good article!

Steve Waclo

OK Allison, I gotta ask.

To what extent does the rain gutter shown in the last photo mitigate the described problem?

I'll take my answer off the air.

Thanks for customarily enlightening work!

Armando

What you expect when builders and homeowners pay $1.00/sf for design services... I love it!!!

Allison Bailes

Good question, Steve. I'm sure others wonder the same thing when they read the article, so I'll answer it here. The gutter was the last thing to go on, so it has no ability to handle water that gets behind the cladding. It also doesn't make up for the lack of kickout flashing because there's a gap between it and the siding.

Allison Bailes

I hear you know a thing or two about design, Armando.

Sean @ SLS

To add on to that, it can actually make things worse if it is sloped incorrectly, becomes blocked, etc... as water will overflow into the areas next to it. If you add in some leaves into that gap you are really going to speed the process up.

Maybe I am missing it / reading it incorrectly but ice/water should have also been placed at that intersection of the wall to the fascia which would then have been overlapped - http://thehtrc.com/2013/getting-details-right-roof-flashing

Armando - that is what we call job security

Allison Bailes

No, Sean, you're not missing it. That's OSB you're seeing where you say you should see the peel-and-stick flashing.

Ryan Shanahan

I'm concerned that water might still find it's way into that window assembly via the flashing tape at the top of the window that protrudes further out to the sides than the flap of house wrap the covers the majority of it. I think it's relatively minor but ideally there should be zero reverse laps correct?

Allison Bailes

Yeah, I said it was better than the usual but not perfect. What do you expect from the builder who made those other mistakes?

Walter Stachowicz

There are several other glaring discrepancies here. The housewrap should have been installed with plastic cap fasteners, not staples. The flap on the top of the window should have tape on the diagonal cut on the left side. And it is not wise to mix and match brands of WRB materials. Some are acrylic based and some are butyl based. Notwithstanding the poor application, not one of the 3 manufacturers would live up to any product warranty if a claim were made.