Recessed Windows – A Foolproof Install Method

Recessed windows are becoming more common in the southwest. It's a nice architectural detail, but it's actually a pretty tricky waterproofing detail. Most often when I see these on a home under construction, I'm seeing these recessed windows installed in a fashion that will surely lead to a leak.

It's pretty obvious this recessed window is going to leak!

Anytime you see a sheet of “housewrap” used on a flat portion of a house you should Scream "No!" This is surely a leak waiting to happen.

I took those two horrible pictures above a few years ago when I was first researching how to install recessed windows for a client that wanted this detail. Now that I'd done a few projects with RW's I have a hard time not slowing down my truck when I see another builder using this detail.

From a distance this doesn’t look correct. Look at the paper flashing for the sill. I had concerns even from my truck.

Now the red flags are really raised! Anytime you see bare wood and 90-degree cuts on straight flashing, there will be issues.

Here's an example (photos above) of a project I drove by recently and could tell from the street that these windows were installed incorrectly. You always need to look at a window install with your “raindrop” glasses on. If you see something that doesn't look correct (bare wood, mis-lapped flashing, etc) then it's time to put the project on pause to find a better way. When I saw this home being built with recessed windows that I suspected would leak I called the builder to see if he would be open to having me show him the correct method. I found the builders sign and humbly left him a voicemail. To his credit, he called me back and I did my best to tell him in the nicest way that the windows he installed were a huge liability and he should fixing them now when it won't be too costly. I figured this might be a good opportunity for a video, so I offered to bring my crew over to his job to pull two windows and show him how to install correctly. I asked for his permission to video in exchange. He agreed.

Here's the work we did:

The window sills were framed flat, but I like to bevel the 2x sill by 5% so it has positive slope.

Then we sawzalled out a small chunk so we could add shims below.

Shims make an easy fix to this flat framed sill.

The first step in installing these correctly was to remove the windows and all the flashing that was incorrect. We want to start back at the bare rough opening. This builder was using Huber Zip sheathing that already has a weather-barrier integrated into the sheathing.

You want to assume that any window has the potential for leakage so making a good waterproof sill is a top priority. I also like to slope the 2x sill by about 5% so that drainage is built-in before I apply my flashing. We used a sawzall to cut the jamb then shimmed under the 2×4 sill to give a positive slope.

For recessed windows I really like a new generation of housewraps called “fluid applied weather barriers”. If you are using Zip sheathing they make a single component flashing called “Liquid Flash” that's designed for their system and takes the place of their Zip Tape or Stretch Tape. It's a fiber-reinforced “caulking” for lack of a better term that comes out rather thick but is easy to tool and shape. It's idea for this recessed window because it's nearly foolproof. Just gun it onto the Zip sheathing & the bare pine rough opening and tool it out with a plastic trowel. It's not cheap at about $30/tube but it's super simple and easy to install. You'll need about a tube per rough opening.

Our carpenters picked up this new product really easily. Use a standard caulking gun and the flashing origami is eliminated. You can also use this Zip Liquid Flash on penetrations and I coached this builder to use it for their hose bibs, hvac vent, and electrical stub-outs through the Zip sheathing. It's an impressive product.

Here's the finished rough opening with the Zip Liquid Flash. Very simple and straightforward. Now we have an opening that's truly water-tight. Now, when my cladding leaks I'm not worried about water getting into my framing.

The rough opening with zip liquid flash is now ready for the window install.

Standard window install method here. We tend to use dap dynaflex 920 on our nailing flanges. Caulk the back side in an inverted “u” shape and leave off the caulk at the sill.

Then after the window is installed and nailed you’ll go back over the nailing flange with more zip liquid flashing. It sticks to the previous liquid flash and you’ve got a water-tight window now!

Another option for a fluid applied weather barrier that could be used on the entire house is PolyWall's Blue Barrier system. This is a two part system and the first step is their PolyWall Blue Barrier Joint Filler 2200. This comes in 20 oz. sausage yubes (you'll need a special caulking gun for this) and goes on first to fill and gaps/cracks and joints. If you were coating the whole house you would also use this at your sheathing joints as well using it to seal all penetrations in the envelope (hose bibs, ducts, wires, etc). This is a more dense caulking that's fiber-reinforced and will bridge up to a 1/2-inch gap.

The foam fills the gap and gives the Blue Barrier 2200 a way to span the gap.

Once you've used the Joint Filler you'll switch to the Blue Barrier 2400 Flash n Wrap. This is a more viscous fluid that can be used as a “housewrap” rolled onto the whole house. In this case we are using it over the Zip wall but again the advantage is that it is foolproof in the install. We coat all the way into the RO, then over the edge of the sheathing by 6” and now we have a waterproof opening.

Blue Barrier Flash N Wrap 2400 is slightly thinner viscosity than the very thick 2400.

Lastly, we will install the window as normal but there is one final step that's critical. We want to back-caulk the frame of the window to the jamb. This will give us an air-tight window but will also act as a back-stop to keep any water that gets through the frame from not backing up into the window.

Here is the finished install. The window on the left we used Huber’s Zip Liquid Flash, the blue one on the right uses Poly Wall’s Blue Barrier. As you can see this house has no overhangs and with these recessed windows you need a “Bomber” system to waterpoof. Fluid Applied wins.

You will also use this fluid applied over the window flange on the outside, but only in the upside-down “U” shape. Don't caulk over the nailing flange at the sill. This will give a spot for any water that leaks into the window to find a path back out.