In areas with expansive soils sticking doors, doors that will not latch, doors with distorted striker plates, and doors that do not fit squarely on the door frame are all possible indicators of possible foundation distortion due to swelling soils. But in many cases, perhaps a majority of cases, the cause is not swelling and shrinking soils. What else would cause door issues? Here are the main culprits:
Problems with door shims
First, watch the 7-minute YouTube video:
If you watched the video on how to install a pre-hung door you will notice that a lot of the work revolves around shims. Shims are used to hold the door frame in place as adjustments are made by the installer. Note that when everything is aligned so the door is level and plumb, the next step is to use a small nail to secure the shims in place. The shims are necessary to keep the door assembly level and plumb for the life of the house or the life of the door.
Now imagine that over a long time things begin to happen. Kids, especially boys, learn to stand on a chair and jump while grabbing the top of the door so they can swing like Tarzan. That is just one example.
Ordinary wear and tear over a 20-year period can easily result in loose shims, shims that have fallen down, etc.
Hinge screws that are too short
The screws that are used to secure the hinges to the wall frame are around 5/8th inches long. This is too short. They work for a while but if you use the 5/8th inch screw, the door hinges will not be screwed using a screw long enough to secure the door hinges to the trimmer stud in the wall frame.
One way I check for this is to open the door, grab the doorknob, and try to push the door away from you while using the doorknob to pull the door toward you. If the connections are loose the door can easily be “rocked”.
To some degree, age comes into play. The temperature and humidity in the house varies with the weather. This causes construction materials, especially wood, to shrink and swell.
As a slab on ground ages changes begin to take place. Typically the foundation will distort into an upside-down bowl shape. This is expected so long as structural safety or integrity issues are avoided.
If you watched the video above, you may remember that the height of the slab was an inch off from one side of the door to the other. One inch is a lot comments the homeowner and the carpenter agrees that it is a lot.
It could also be due to sloppy finish work.
Sagging of the frame structure
Wood frame structures sag over time. It is a material property. Consider a door opening in an upstairs bedroom. On the left side of the opening, the king and trimmer studs are directly below so the load from these studs is well supported with minimal deflection in the floor.
On the right side of the opening, the trimmer and king studs sit on the floor decking between two floor joists. It is inevitable that the loads from the king and trimmer studs will force the floor decking to sag.