Flashing the Rough Opening

If you are also going to side the house, now is a good time to flash the opening. This isn't always needed, if the old flashing is in good shape, but a lot of older homes weren't even flashed at all. If you aren't doing siding though, you'll have to just try to make the best of what you have. Look for holes in any flashing, and if you see water stains, see if you can slide a piece of roofing felt in between the siding and the sheathing. Bend it over the framing and apply 100% clear silicon underneath it to secure it and provide a dam to keep water out.

If you have ripped off the old siding, or are installing new siding over top of it, you can flash the window like new. You can cut the roofing felt into strips about 12" wide. Put the bottom piece on first. Cut it's length so that it goes past both sides of the window about 8". Cut it to fit and then nail it in place on the rough opening. I like to lap the bottom edge on the top edge of a piece of siding, this helps get water back to the outside of the siding where it belongs. Since you don't know yet where the siding will come to, you leave the bottom of the flashing loose. When you side up to it, you can trim it so that it just lays on the top edge of the siding. Then apply silicon underneath it and you'll have a great barrier for water. You can use button nails to hold it down in the corners. These are the same type used when applying roofing felt on a roof.

Flashing the Sides

The sides go on next. They are the same width and you want to make sure that they protrude about 8" past the top and bottom of the window. You will lay the bottom end over top of the bottom piece of flashing. You have to cut a miter at the bottom so it bends at the corner. The purpose of this is that if water gets behind the siding, it will run down the felt and past the opening, eventually running out the bottom.

The Top Piece

The top piece of flashing is cut the same length as the bottom. The only difference is that the top piece overlaps the side pieces, like a shingle. Again, apply adequate silicon and mash it down. Use button caps to secure it, as few as is necessary.

The Opening is Ready

Now that the window is removed, the opening is clean and any flashing work is done, you're ready to install your First Window!