One of the biggest obstacles to properly installing a basement egress window is the potential for the accumulation of moisture either around the window or within the egress well itself. Proper construction of the egress window and well is essential for avoiding this eventuality.
The likelihood that the addition of an egress well will suddenly cause your otherwise dry basement to flood is low, but it is nonetheless important that you take the steps to ensure proper drainage. With the proper slope of the trench, the use of consecutive layers of gravel, treated wood, and flashing around the window, the most common moisture problems can largely be avoided.
Slope of Trench
When excavating the trench for the installation of the egress well, it is important that the bottom of the trench slope away from the foundation. Soil, especially soil with high clay content, holds water very well. If the trench is flat or sloped towards the foundation, it will encourage the water to gather against it. After time, that can be very bad for the home’s support structure. By sloping the trench away from the home, you provide a means for water to run away.
Layers of Gravel
Two 3-inch layers of gravel should be placed over the well trench you dig. You may choose to dig all the way down to the bottom edge of the foundation and fill the entire hole with gravel. You may stop at the downward sloping trench approximately 1-foot below the bottom edge of the window. Layers of gravel ensure the maximum amount of drainage. Important too is that you lay down a sheet of landscape fabric below all gravel to prevent the soil below from clogging the gravel drain.
The wood used to frame in the window should be pressure-treated to withstand moisture damage. The wood will be capped on the outside, but it is important that it not be allowed to rot after time. Basements are typically moister than other areas of the house. This fact combined with the new exposure to the outside will eventually damage the frame around the window.
Window Flashing, Drip Cap, and Vapor Barrier
Install metal or plastic flashing strips on the outside edges of the egress window to block moisture from entering the basement between the window frame and the wall. Flashing may also fit across the top of the window frame, but you may also find that using a drip cap along the top increases moisture protection. Those two items together with an internal vapor barrier will prevent moisture from seeping through the window.
Avoiding moisture issues with basement egress windows and wells is a matter of proper planning and utilization of the available materials. By not cutting corners and taking the time to install the right components, moisture accumulation should never be a problem.