Installing flangeless windows in wall with 6″ exterior EPS insulation
I am building a new house in southern Ontario, Canada. The exterior walls will be constructed using standard 2×4 framing, with OSB sheathing (which will be the air barrier), and then 6″ of rigid EPS (GPS, actually) insulation. The plan is for house wrap over the insulation as WRB, then 3/4″ strapping, with long screws into the studs to hold the insulation in place. Vinyl siding will be mounted to the strapping.
The windows are triple-glazed European tilt&turn, with no flanges. I want to install them at or near the outside of the wall surface to maximize the useful interior window sill width.
I have read the very useful article here:
But I’m not sure of the construction details of the plywood window bucks. The triple glazed windows will be quite heavy. We have several 60″ x 60″ windows on the south side of the house. The plywood cantilevered buck seems a rather flimsy thing to hold up all that glass 6″ out from the framed wall.
How should the corners of the buck be constructed to take the load?
The suggestion of a 2×4 under the outer edge of the buck sill makes sense, but does it need to be supported somehow, or is it only transferring load from the center of the sill to the corners of the buck?
Thanks for any advice.