How to Add Flashing to a Basement Egress Window

What You'll Need
Safety glasses
Measuring tape
Silicone sealant
Nail Puller
Pry bar
Putty knife
Water and bleach
Spray bottle
Nail set

If you want to avoid water from leaking into a basement egress window, you’ll likely install flashing to it. You can get flashing in vinyl, sheet metal or tape. The latter is the newest form of flashing but it could degrade in extreme temperatures or when exposed to ultraviolet light. Sheet metal is widely used but can be difficult to work with and vinyl is inexpensive but not as strong as sheet metal. It is imperative that it be installed correctly or it will allow water to enter and you could experience wood rot. You can install flashing yourself to a rough opening or to an existing window.

Installing Flashing to a Rough Opening 

Step 1 – Choose Your Flashing 

There are a couple types that are highly recommended: 30 lb. felt bituminous impregnated kraft paper or the commonly used sheet metal flashing (aluminum or galvanized steel.) The best width is 12 inches with 9 inches as the minimum. 

Step 2 – Where to Start 

Start from the bottom, working your way to the top. There will be overlapping but that is desirable.

Step 3 – Sill Flashing 

Install the sill flashing by putting it across the bottom of the rough opening. Use your measuring tape to make sure you cut it so that it overhangs by about ½-inch on each end. 

Step 4 – Jamb Flashing 

Install the jamb flashing from above the apex of the rough opening to below the base of the sill flashing. It will overlap with the sill flashing. 

Step 5 – Secure Window 

After you’ve secured the window in place, install the head flashing across the top of your window, going further than the jamb flashing on both sides. The top edge of the flashing is adhered to the construction and the bottom is installed over the head fin. 

Applying Flashing to Existing Window 

Step 1 – Remove Nails 

Remove nails from the upper window edge using your nail puller.

Step 2 – Loosen Siding 

Using your pry bar, loosen the siding a bit so that you’ll be able to fit the flashing underneath it. 

Step 3 – Scrape 

Scrape out any old caulk with a putty knife. 

Step 4 – Mix and Spray 

Mix water and bleach in a spray bottle. Spray it on the casing to remove any rubble. Don’t forget your gloves and safety glasses. 

Step 5 – Seal 

Apply a thin line of silicone sealant to keep water from getting into the casing and siding. 

Step 6 – Apply Flashing 

Measure and cut your aluminum flashing so that it will overhang by ½-inch. Apply flashing as outlined above, starting at the sill and finishing at the top, overlapping with flashing already in place.   

Step 7 – Nail it Down 

Slip the flashing under the siding. Using your nail set, sink the nails into the pre-existing holes. Fill the nail holes with putty and sand when dry.