Window & Door Leaks & Condensation

Window and door leaks are a common occurrence. They result from a number of causes, including installation errors regarding sealing and flashing, deterioration of the sealants, water seepage, and wind-driven rain.

Careful detailing is required during the installation of window and doors. Recommended flashings and sealant methods vary with circumstances, and are therefore not discussed in detail here. New building owners should confirm with their designer, contractor or project manager how this is to be done, and why the intended method is the best for their particular project. They should then confirm what they are told with the window manufacturer.

Water seepage through a door threshold can result from an improper or inadequate slope at the exterior stoop. When the surface outside a door is not pitched away from the structure, rainwater drains toward the entry, increasing the potential for intrusion beneath the door.

A window or door leaking during a high wind event does not necessarily mean that it is structurally damaged. This is because typical fenestration (water) testing pressure thresholds are well below structural standards. For instance, a window may constructed to structurally withstand 50 lbf per square foot (psf) pressure, whereas the fenestration (leakage) testing would pass if the window doesn’t leak before only approximately 15% of that, or 7.5 psf. This equates to roughly 1/2 the wind speed.

Interior condensation on window and door glass panes, while not an actual leak, can contribute to damages beneath or adjacent to a window or door. This can mimic the damages caused by a rainwater leak from the exterior. Interior condensation occurs when relatively moist interior air comes into contact with glass pains cooled from the exterior. Moisture in the interior air condenses and builds up on the window or door glass. Single pane glass is particularly susceptible to this. Potential solutions include reducing interior humidity, changing the windows, or temporarily covering the windows with poly sheeting.

ADDITIONAL RESOURCES:

NAHB Technote: Window and Door Flashing: Code Requirements and Best Practices

Manufacturer’s Installation Guides