A wood door sticks each season for one of two reasons: by a shifting foundation or moisture penetration into the door or around it.
In the summer you can hardly get them open. I fight with the doors, kicking and pushing until I finally work them open. It is not due to paint build-up on the edge of the door.
As the frost comes out of the ground in the spring it can raise or lower a porch or stoop and cause a door to bind. Moisture in the ground expands earth and clay and exerts extreme force upon a building. We’ve discovered the power of wet earth when many additions settled during the drought last year. Many of those structures should be rising back up thanks to all the rain we’ve been getting this summer.
Check in the basement under and around the binding door. Are there any cracks in the wall? This would be an indicator of a shifting foundation. There is no easy cure for this except to force surface water away from the house. If the earth is kept dry at the footings they will move less season to season.
Sometimes the shrinking and swelling of wood cause the binding. Either the lumber surrounding the door or the door itself is taking on water. When wood gets wet it swells. Check the siding or bricks for gaps or cracks that let water penetrate into the house or on to the door. The house itself could require caulking or even a flashing to prevent water leaks.
If water can come in direct contact with the door make sure it is properly sealed both top and bottom. Too often attention is placed on the surface of a door and none on the top and bottom. Water, due to capillary action, loves to suck into the ‘end grain’ of lumber. Once there, the wood will swell and then cause a door to stick in the opening.
If pitching the ground so water flows away from the house, caulking the area around the door, or even painting the edges of the door can’t cure your problem, there is still a remedy.
Plane the edges of the door until there is at least a one-eighth-inch gap between the door and the jamb. This can be done with a block plane, a rasp or Surform file, or a belt sander. Don’t attempt this with a palm or vibrating sander; they don’t remove enough material fast enough to do the job properly.
Then either paint or varnish the edges to seal them. Don’t forget to put at least two coats on the top and bottom of the door.
To finish the job the door needs weather-stripping to seal out the elements of nature. Here is the secret cure; us a ‘bumper type’ weather-strip. It’s not unlike the way the seal works on a refrigerator. It mounts on the doorstop around the outside of the door. It bumps against the surface of the door, not the edges. If the door shifts up or down in the opening, it won’t bind on an edge weather-strip.