Video: How To Flash a Rough Opening
Everything looks pretty good here, so the next step is to install drainage at the sill and layers of flashing all around the rough opening. This may be the most important part of this whole job. I’ve taken enough houses apart to know that water will eventually find a way to get behind the siding and trim, no matter how well they are installed. These layers of flashing protect the house’s framing from water and rot. The first thing I am going to do is create some simple drainage at the sill to shed any water that does get in away from the house
I use a piece of factory-primed beveled siding to create drainage. I fasten the siding with spray-foam adhesive and screws. You may have seen this technique used for window installations.
Flexible flashing products are tenaciously sticky, so before installing the first piece over the sill, I draw a plumb line on the sheathing. This way I can line up the edge of the flashing, and know that it will run parallel with the sill.
The first piece of flashing extends across the bottom of the opening. I make a slit on each end that allows the flashing to wrap over the sill and extend up the face of the wall.
Small bow-tie-shaped piece of flashing, made by doubling the flashing on itself and cutting it into a triangle, cover the critical area where the outer edge of the bottom plate meets the sill.
I cover each side of the rough opening with two pieces of flashing. The first covers the bottom half of the opening, lapping the sill flashing as far as possible. The second laps over the first and extends to the top of the opening, where the sequence is reversed: Bow ties first, then the last piece of flashing which extends across the top of the opening, lapping the side pieces as much as possible.
There are a lot of pieces of flashing to install, but the idea is always the same: Like installing house wrap or siding, you always work in layers from the bottom up when flashing. Now we can move on to one of the more fun part of the job, trimming the door.