Q FROM ROB: "When we moved into our house, the previous owner had installed 2 solid wood doors going to the upstairs bedrooms, but didn't bother to paint or prime them.
So last spring I decided to paint them. I just did 2 coats of standard interior paint. I did a fairly thorough job, but I probably didn't do the bottom of the door. That was fine, until the summer came, when the doors decided to soak up all the humidity and outgrow the size of the door opening, so they couldn't close all the way. It was really annoying.
It looks like they've finally lost all of that moisture, since you can close the doors again. I think one of them might have gotten a little warped during the process, but its not too bad.
Do you have any recommendations for what I could do to prevent them from expanding again this summer? Should I apply another layer of paint and make sure that there are no exposed areas? Do I need to get a special kind of paint? Do I need to strip off the paint I have? Or is this a normal thing and I should just shave off some of the top/side so that it has room to expand each summer?"
Most solid wood doors are frame-and-panel doors, like the one pictured above. That greatly minimizes movement, because only the 8' of the two outside frame pieces are expanding, instead of the entire 30" width of the door. The panels actually float inside the frames, entirely unfastened, which leaves them 1/2" or so of room to move that won't affect the overall width of the door. (However, it's not fool-proof. That same door sticks so badly that one of the frame pieces actually split. You can see the aftermath below.)
A strong finish is the best way to minimize the effect of wood movement. Two or three coats of interior trim paint should do the trick nicely, and you don't need to paint the bottom edge. If you want to see wood grain, use a hefty polyurethane.
If the doors are still sticking, your only option is to plane or cut them down. I would wait until August, and then re-cut them to just barely fit in the frames. If you cut them too small, you risk them shrinking so much that the latches don't close in winter.