Dan Morrison | November 07, 2017

details // WRB & Flashing, Windows & Doors

A Window Install in a Thick ZIP Wall


The general idea of installing windows is to plug the big hole that you just cut in the wall


The bottom should slope out and away from the house, and the rough opening should be protected with flashing tape.

Shim the corners of the window so it will be level and then caulk the sides and top against water and air leaks.

When the window is level, nail the bottom corners.

Measuring diagonally and shimming the top corners ensures that the window is square and that it will operate properly. 

Now, he nails off the perimeter and tapes the side and top flanges against water or air leaks.

The bottom is left untaped for drainage.

And to help it along, Ben installs little shims to create a drainage channel.

The inside is sealed with special tape, backer rod, and sealant, or low-expansion foam.


—This detail was executed at Professional Remodeler's 2017 Model Remodel, built by Ben Bogie, Built to Last Design & Build.



Thanks for video.:

1.  Can you spec how you create the pitched sill, and approx what pitch?

2.  Also, how much do you change the "standard / published" rough opening to account for this detail?


Carl Bruen

Bruen Design Build, Inc.

Morristown, NJ



Daniel Morrison's picture

In the animation, we showed a piece of beveled siding put atop the window sill. It is not a drastic slope, but it doesn't have to be for gravity to direct water the right way. 

Here are a couple more thoughts:

1/ We posted a video series about installing 'Outies' in a wall with thick exterior insulation where the framing didn't need to be sloped because the foam was thick enough that the window didn't extend into the framing, so the foam was sloped (cutting it away at the opening with a long razor knife.

video series: https://www.protradecraft.com/outie-window-installation-weave-it-exterio...

animation: https://www.protradecraft.com/outie-window-details-walls-thick-exterior-...

2/ In one of out podcasts, Architectural Projections, engineer Sarah Gray says anything greater than about 1 degree will work:

"I would say anything greater than an eighth of an inch per foot, or greater than 1%, works well enough, perhaps a little more slope at the top cornice or capstone at the very top of the building, because that's what sees the brunt.

More slope is better, but if you get it too sloped and too angled, sometimes the architects get a knot in their knickers and don't like the look of that."

Hope that helps,


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