Windows are one of the most common sources of leaks in new buildings. A simple inspection routine before the siding or cladding goes on catches problems while they are still cheap to fix.
In this article
Why windows leak
Wrong flashing order, missing sill pans and gaps in the weather barrier.
Sequence
The weather barrier and flashing must lap like shingles, so water always flows out.
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Sill pans
A sloped sill pan sends water out instead of into the wall.
Sealants
Follow the manufacturer. Too much sealant in the wrong place can trap water.
First window
Inspect the first installation with the installer before the rest go in.
Water testing
Test a sample of windows before closing the walls.
Documentation
Photos of each elevation before the cladding goes on.
Getting started
Write a one-page window inspection checklist with photos of correct details.
Common mistakes
Reverse lapping, skipping sill pans and covering windows before inspection.
Example
A contractor started testing the first window on each elevation before siding. On one project, the test showed a missing sill pan detail across all units. The fix took a day instead of months of warranty leaks.
Inspection checklist
Weather barrier lapped correctly, sill pan installed and sloped, side and head flashing in the right order, fasteners as specified, and sealant only where the manufacturer requires it. Photo of each item before covering.
Training installers
Walk the first window with the crew and photograph it as the standard for the rest of the project.
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Frequently asked questions
Should windows be water tested during construction?
Testing a sample of windows before the cladding is installed is a good practice on many projects. Some specifications require it. It is much cheaper to fix a leak before the walls are closed.