Installing a new threshold
It’s important for a door to fit snugly against its new vinyl-gasket threshold, particularly if the system you’re using doesn’t include a door-bottom sweep. But fitting an old door with one means having to trim the door bottom very accurately.
Before removing the door from its hinges to install the threshold, I put a piece of tape down low on the face of the door and another across from it on the face of the stop (or its equivalent on a rabbeted jamb), as shown in the drawing. Then I make a single pencil line across the two as a registration mark, and I remove the door. Once I’ve installed the new threshold, I can then measure from the top of the gasket to the pencil mark on the stop and transfer this number to the door by measuring from its registration mark down. I usually add 1/16 in. to get my cutline — this will ensure good compression when the door is closed.
Rod Goettelmann, Vincentown, NJ