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Detail Library

Exterior Insulation Retrofit for Existing Bay Window

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.

For more on windows:

GBA Encyclopedia topic page

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.

Even the best window details can be hard to follow because so much depends on the sequence of installation. Use the GreenBuildingAdvisor window installation series along with these window details:

Flashing Details

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