Window and door flashing - AK House Project

Water that enters and becomes trapped inside a wood-framed wall can cause mold and rot, leading to long-term structural damage. Unfortunately, window and door openings provide big targets for water intrusion, and mistakes can be costly. So what’s the solution? Good flashing. The term “flashing” is both a noun and a verb, and refers to components and techniques designed to repel and manage water at these openings. A properly flashed window will prevent air and water movement and keep building components dry and intact. A poorly flashed window can cause a wall to fail within a few years or less.

In the past, many windows and doors were not flashed at all, or builders simply “flashed” them by folding housewrap over the inside of the openings and calling it good. Today, builders typically use plastic and/or metal components and heavy-duty tapes that beef up the waterproofing at the openings and shed intruding water to the outside. These products must be installed precisely and often in a specific order so that water cannot creep under the edges of tapes or become trapped behind windows. Errors are not uncommon.

More recently, a new crop of “fluid-applied” flashing products have entered the market. These products come in a viscous form and are rolled, brushed, sprayed, or troweled around the rough opening, where they dry to a thick rubbery consistency. The advantages of fluid-applied products are that installation is simple and they form a totally seamless, durable final product that easily conforms to unusual shapes. The downside is cost: right now, they’re much more expensive than most tape-based systems.

I used Prosoco’s fluid-applied Fast Flash to flash my rough openings. I sealed the seams with their Joint and Seam product and then troweled Fast Flash around the entire inside of the rough opening and over about four inches of the exterior sheathing. The product has been easy to work with. It’s extremely sticky, dries pretty quickly and can even be applied in light rain. Once applied, water beads on it and runs off.