How Do I Deal with Patio Runoff?
Keeping the rain from infiltrating
I have a patio and an inside floor at about the same height. Water often runs under the threshold and is rotting out the door frame and baseboards. How can I stop this seepage?
— Cory, China Spring, Texas
Tom Silva replies: The whole door unit needs to come out — frame and all — and you need to install a bituthane or an ice and water shield seal along the threshold and up six to eight inches on both sides of the opening. This sealer should be wider than the threshold so that you can fold it into a ridge just back from the front edge of the threshold; this ridge creates a dam. Once you've created this ridge, wrap the remaining sealer tightly against the edge of the threshold. Before the door gets put in place, you need to place a bead of latex caulking between the siding and the trim on top of the bituthane, all along the door opening. Then take a piece of cut-off mastic, water stop (used in rubber roof applications), butyl, or silicone (in that order of preference) and run that in front of the ridge you formed. Now when you put the door back in place, it will drop onto the caulking and cut-off mastic, sealing its perimeter and keeping water from infiltrating, even if it does penetrate the siding.