Best practices for flashing, sealing, and thresholds

In Denver, there is a mold sniffing dog named Buddy. If Buddy can get his nose near mold, he will signal it every time. It’s incredible, and in our small mold knowledge community, he is very well known. 

Buddy unfortunately signals a lot in the areas under windows during his inspections. Subsequently, when the drywall is removed, microbial growth is indeed found. Why? The greatest cause for mold under windows is improper installation, whether 50 years ago, or last year. 

Windows fill actual holes in the wall, and the hole is a week link,, providing easy access for water to enter the home. The greatest areas of potential intrusion are the top and bottom of the window for different reasons. If a window doesn’t have the correct flashing above the window, driving rain can work its way behind the window structure and into the wall. 

At the bottom of all windows are “weep holes,” which exist to remove water that strikes the window and cascades down to the sill (bottom) and needs a way out of the track system. The problem is these holes can become clogged and it’s very important to keep the inside track free of debris so the weep hole works correctly. In addition to the need to keep weep holes clean, it is also important to ensure water that drains out of them flows properly down the trim and siding, rather than migrating behind the siding to the wall system. The window must be wrapped correctly to avoid this problem. 

If the bottom, sides and top of the window, siding trim, or flashing aren’t installed properly, water will easily find its way into the wall system, and gravity will take over.