10/07/2026
Deep window sills are a dead giveaway for a high-performance house. This wall is thick. But why?
Window placement is a design choice, but it's also about thermal bridging (heat sneaking through the framing).
Here's what's in this wall, from the outside in: back-vented siding over a rain screen gap, a weather-resistant membrane, 4 inches of wood-fiber rigid insulation, the structural wall, taped plywood that acts as the air barrier, and a 2x4 service cavity filled with dense-pack cellulose for wiring and plumbing.
Each layer has a job. The rain screen keeps water out, the rigid insulation keeps heat in, and the taped plywood stops air leaks. It adds up!
Cascadia Windows
BC Passive House
📐Julie Kriegh Architecture