European window brick installation – GreenBuildingAdvisor

I would really appreciate if you could please give some advice given your knowledge of US construction and European windows. As someone originally from Europe, I’ve long planned to replace the existing double-sash wood frame windows with the European models I’m accustomed to. What I didn’t anticipate were the complexities introduced by U.S. construction practices.

My house (1989 built) has a brick exterior with a 1¼” air gap between the brick and the framing/sheathing (which appears to be aluminum-faced fiberboard).

The current wood windows are installed in the middle plane, recessed 2.5″ into 3.5″ wide bricks. Oddly, the rough openings are smaller than the brick openings, so I plan to resize the rough openings from the interior to match the outside brick opening dimensions.

I’m installing flangeless Aluplast windows (2.75″ deep) and sealing with hi-performance European tapes, backer rods, and Siga Meltell. Fastening will be done with Wurth AMO 152mm masonry screws and anchors to the 2×4 framing.

The installation challenge that I have is that the 2.75″ window frame depth doesn’t span the full distance from the brick to the 2×4 RO due to the air 1.15” gap (see Pic 1 in the attached file)

My workaround to bridge this gap is:

1. Push Foamular XPS 2”x1”25 arranged in an inverted V-slope shape between the sheathing and brick to create a first water diversion flashing (see Pic 2). Then install head flashing under it with edges that extend over the window width so that any water that might come from above would be diverted somewhere in this sheathing-brick gap

2. build a window buck out PVC (impervious to water) screwed to the RO and extending up to the brick opening. Its edges would be sealed at the top and sides with a bead of PU closed cell and then taped between the exterior brick and PVC with Fentrim 430 from the inside (I cannot access the outside). Bottom would be sloped and left open to shed any water that gets inside the window buck.

3. place the window 2″ offset from the façade, with 1.5″ resting on brick, ¼” air gap, and 1″ (2.75” window depth – 1.5” – 0.25”) on the 2×6 sill plate (inside the PVC box). In practice, on the front side of the house, the window will not actually rest on the brick, as the brick sill will be installed only after the window is anchored to the brick wall. Unfortunately, while the rear elevation of the house has existing brick sills, the front still relies on wood sills, which will need to be removed and replaced with brick post-window installation to match the overall design intent. However, the window will be anchored with cement structural screws (Wurth Amo) in the brick and, as mentioned, placed 1” on the 2×6 taped sill.

4. The window will be sealed with backer rod and Siga on the exterior, then with Air Dam from Proseco (or PU closed cell) and Fentrim IS 20 on the inside.

5. The 2×6 sill will be sloped and have a wood strip acting as a water dam. Fentrim 430 on the exterior side of the sill (in the sheathing-brick gap) and IS 20 on the interior

I tried to read everything that relates to my case (brick exterior, frame build) on this website and elsewhere but I would appreciate your advice on latest methods and your candid advice on my suggested solution. Unfortunately, I tend to over-engineer things (according to my wife) and welcome any suggestion to improve my design.

Also, for the exterior do you have a better caulk suggestion other than the Siga Meltell?

Unfortunately, my attachment could not load  – will try later.

Thank you in advance for your kind help!