A good window installation converts a hole in the wall into an integrated part of all three important barriers that make up a wall assembly: the air, thermal, and water barriers.

Because all windows leak at some point, rough openings need to be designed to handle water entry. The rough sill should be flashed with either a pre-formed manufactured sill pan or a site-built pan.

This detail shows a site-built sill pan installed in a wall sheathed with rigid foam. The outside face of the foam is the wall’s drainage plane.

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Video Series: Flashing a Window in a Foam-Sheathed Wall

The toughest details are those that have to match up with someone else's work, or those done — even done well — when energy was really cheap. These details are a collection of some common — and tough — dovetails of existing work with retrofits or additions. Bear in mind that green remodeling means creating a new operating regime that is better, not worse, than the one that may well have been working just fine before. Integration of energy efficiency, moisture management, and indoor air quality is much more important and challenging in remodeling than in new construction.

All of the GBA window details reflect two basic principles: Flash and drain both the rough opening and the window unit; and weatherlap all components as much as possible. The inclusion of both rigid exterior insulation and a vented air space in just about all of the details means that there are many ways to achieve flashed and properly weatherlapped rough openings and window units. Check out more than one sill or head detail to see different ways of skinning the same cat.

Even the best window details can be hard to…