Question
I have a new (4 years old) house and noted that the patio door was jamming in its frame. The builder came out and did adjustments each year. Now we discovered that the wood below the door frame is rotten, and even the deck attachment to the house is starting to rot. The reason the door jammed was the slow sinking of the wood below the door.
The builder said he would replace the door and fix the rot. Since the warranty is now running out, I am worried that the door will rot in the same way in another 4 years. How do should this be fixed and how do we avoid this happening again.
Answer
Patio doors are notorious for serious rain leaks. Either the mitre joints at the corners, screw fastenings through the frame, hardware openings allow water through the frame or water leaks through failed caulking around the installation opening, or meltwater flows back over the threshold. Windows leak just about as often. See the figure.
The solution is simple - assume the door and its installation will leak, provide a sub-sill flashing that directs water to the exterior. To prevent meltwater from snow that collects against the base of the door from leaking inward, drop the deck a few inches. The rot at the rim joist level can be controlled by leaving a large enough gap between the rim joist and the deck ledger board. About 1/8" should be enough to not trap water and allow fast drying.
