Windows in Thick Walls
Updated: Jan 5
Thick-wall assemblies offer better comfort and energy efficiency, but installing windows presents a challenge for builders.
Thick, highly insulated walls are great for lowering energy bills and creating a more comfortable interior environment for occupants, but they present some unique challenges for builders when it comes to installing windows and doors.
The aesthetics are determined in part by the size of the window, but the thickness of the wall can make the choice even more critical. Moving the window away from the outside of the wall requires exterior jamb extensions made from either the trim material or exterior siding. The farther inward the window moves, the more you accentuate the thickness of the wall.
Performance. Next you need to consider comfort and the thermal performance of the window. From a thermal perspective, a window really should be placed in the center third of the opening to put it in the middle of the wall’s “R” value—not too cold, not too warm, but just right.
Placing the window in the outer third of the wall puts the window in the colder part of the opening, and you risk creating a microclimate in the window pocket, especially with smaller openings. This microclimate carries the risk of getting cold enough for moisture to condense on the glass (a good reason for triple glazing). A colder glass surface also makes you feel colder when you’re standing next to it. As your body radiates heat toward the colder glass surface, you feel chilly.