Measure the area of the opening where the flashing will be installed. Run a tape measure across the length of the opening.
Measure the width of the sill, and add an extra half inch for the flashing to extend down toward the outside of the house. This will help prevent water from entering the house.
Lay out the flashing along the sill.
Mark on the flashing where cuts for the length or width will need to be made.
Cut along the marks with tin snips, and leave an extra 1/2 inch in the width for the flashing to fold over.
Set the flashing back on top of the sill plate to make sure it fits properly.
Spread out construction adhesive over the bottom of the flashing with a margin trowel. Cover all of the flashing, and set it down on the sill plate.
Press down firmly on the flashing so it can adhere to the sill plate, and run your hands over the flashing to help it adhere.
Fold down the 1/2 inch strip along the outside of the house, and press it in place.
Wipe off any excessive construction adhesive that squirted out from underneath the flashing with a clean rag.
Inspect the area to make sure there is no more adhesive, and verify that the flashing is properly installed.