Is the Window Leaking? Or is it Something Else?
The leak may not be the window.
It might be the transition.
Ask any building envelope consultant where water intrusion starts, and the answer is always the window unit itself — it's often the four-inch perimeter where the window meets the wall.
Request a Design Review →In theory, a window opening is simple. The window sits in a rough opening. Flashing and the wall's water-resistive barrier (WRB) — think of it as the building's rain jacket — work together to form one continuous, uninterrupted path for water to drain to the outside.
In practice, that four-inch perimeter is often the joint venture of two different crews, on two different schedules, following a single detail drawing that neither of them has fully read. That gap between the drawing and the field is where almost every envelope failure we investigate begins.
"Not the window. Not the wall. The transition between them."
The good news: these failures follow a small, predictable pattern. Once you know what to look for, they're straightforward to catch — before the drywall goes up, not after the tenants move in.
How water gets in
01–04 / Field FindingsHead flashing installed backwards
The WRB above the window is supposed to overlap the top edge of the head flashing, so water sheds down and over it. When it's installed the other way — tucked behind the flashing instead of over it — water headed down the wall can drain into the window opening instead of past it.
This reversal is one of the most common defects we find in the field.
Improperly installed sill flashing
The sill pan under the window is meant to catch any water that gets inside and channel it back out. Without raised edges at each corner, that water can simply run off the sides of the pan and into the wall framing at the corners.
They're often on the drawings and improperly installed in the field because they add a few extra minutes per window.
Improper sealant placement
The bead of sealant around a storefront (or flange-less) window frame is the primary line of defense. Storefront windows often only recieve one, sometimes two, lines of sealant and it is rarely installed where the frame meets the waterproofing of the rough opening.
The result is a window that begins to leak shortly after interior finishes are completed.
Flashing sequence can make or break your install
Proper sequencing of flashing membranes, specifically in integral sheathing and 'house wrap' WRB systems are paramount to ensure the window assembly functions for the life of the building.
One layer of flashing membrane, or 'flashing tape', is installed out of sequence or not fully adhered to the WRB and now your asset is left open to water intrusion the next time it rains.
Design review catches it on paper
Every failure above can be found before a single window is ordered — by reviewing the flashing details for constructability, not just technical correctness. A detail can be drawn perfectly and still fail if it asks a crew to work in a sequence the schedule doesn't allow for.
- WRB lap direction checked on all four sides of the opening
- Sill pan geometry and end dams confirmed on the drawings
- Sealant joint width and depth sized for expected movement
- Trade sequencing checked against the actual construction schedule
Field observation catches it in the wall
Even a correct detail still has to be installed correctly. The gap between the drawing and the field is usually a coordination problem, not negligence — and it's most cost-effective to close it at the very first window, before the rest of the floor is glazed.
- First-window inspection before the crew repeats the sequence
- A systemic error at window #2 is a quick fix
- The same error across 200 units is a remediation project
- Early observation costs a fraction of later litigation
Window transition failures are well understood, predictable, and preventable. Reversed laps, improperly installed sill flashing, and missing sealant joints are all findable — with a design review before construction starts, and a field walk at the first window installed.
The cost of prevention is a small fraction of the cost of remediation. The cost of remediation is a small fraction of the cost of litigation.
