It’s easy to find advice on flashing windows. But what about exterior doors? For some reason, most construction experts haven’t provided builders with much advice about flashing doors.
Don’t be fooled, though: The lack of online advice on door flashing doesn’t mean that door flashing is unimportant. If you screw up these details, you can rot out your subfloor and floor joists.
Flashing an exterior door, step by step
- First, read the installation instructions provided by the door manufacturer. Unless these instructions violate basic flashing principles, you should follow these instructions.
- Next, verify that the rough opening is the right size. In most cases, the rough opening should be 1/2 inch higher than the door frame (after accounting for the height of your installed sill pan), and between 1/2 inch and 3/4 inch wider than the door frame. Of course, the rough opening should be level, plumb, and square.
- Install the sill pan according to the sill pan manufacturer’s instructions. (For more information on sill pans, see “Sill Pans for Exterior Doors.”)
If it’s a PVC sill pan, you need to glue the sections together (after fitting them to the opening). Most sill pan manufacturers recommend the installation of three parallel beads of caulk (usually, elastomeric or polyurethane caulk) at the rough threshold before the sill pan is secured in place.
If you prefer to make a site-built sill pan, you can do that. Remember, though, that a site-built sill pan needs either (a) an interior dam, or (b) a positive slope toward the exterior.
4. In most cases, an exterior door shouldn’t be installed until after the water-resistive barrier (WRB) has been installed on the wall. If your walls have conventional housewrap, you’ll need to create a flap in the WRB at the head of the…