What is a sticking door anyway? It's a door that gets stuck in its frame, making it difficult to open and close. A door could start sticking for several reasons. But whether it's due to age, humidity, or loose hinges, it isn't too complicated to get the door to stop sticking and you should be able to do it yourself.
What's causing the door to stick?
As mentioned, there are several ways a door can start sticking. It's important first to determine why a door is sticky - you don't want to start trimming the door down if it's just a matter of a loose hinge. Close the door and look at the way it sits in the door frame. At a glance, you should be able to see if the door is misaligned and where it's sticking. If you can't tell by eye-balling it, slide a piece of paper around the door in the gap between the door and the frame. If the paper gets caught, you'll know where the issue is.
Check the hinges. If they're loose the door won't fit properly in its frame and will probably rub against the floor when you open and close it. Use a screwdriver to tighten the screws. Then open and close the door. You may need to adjust the screws some more, either by making them tighter or looser, until the door fits perfectly again.
While we're on the subject, take a look at the hinges. If they're grimy or rusty, that may also impede the door from opening properly. It's likely the door will be squeaky too. Spray some WD-40 into the gap between the pin and hinge plate at the top. Then open and close the door several times to spread the lubricant. If that doesn't work, you'll need to remove the pins from the hinge plates and clean them with steel wool first. Once they're clean, apply the WD-40 and your door should be back on track.
When it comes to determining what's causing an issue in a home, no matter what that issue is, humidity or moisture always seem to make an appearance. A sticking door is no different. Humidity causes wood to expand. If the door only sticks during the summer, it's a seasonal thing that can be resolved with a dehumidifier or air conditioner. Removing the humidity from the air will shrink the door back to the size it's supposed to be. If the humidity isn't a seasonal issue, you may want to trim the door down a little.
Trimming the Door
If you've determined that the door isn't sticking because of the hinges or seasonal humidity, trimming the door is the most permanent solution. You'll need a block plane. A block plane is a tool that makes trimming flat wood surfaces easy. The pros prefer the more expensive models, but there are many affordable options at your local home improvement center, ranging between $9 and $30.
Mark the area on the door that's sticking. Remove the door from its hinges. Make sure the door is closed first - you'll need to rely on the door frame to keep the door in place. You can use pliers to twist and shimmy the pins free. Angling a flat-head screwdriver into the gap and tapping the other end with a hammer will also work. Once you've removed the pins, you should be able to pop the door out, but you might want to get someone to help you - doors can be heavy and unwieldy.
Run the block plane over the edge of the door that you marked before you took it down. You may need to pop the door back into place and trim some more multiple times before it fits just right, but take care not to trim it too much. Once you've trimmed the door down to the perfect size, use sandpaper to smooth it out. If you want your door to look perfect, you can touch up the area with some paint or sealant.
Sticky No More
That wasn't so bad now, was it? Your door should be working just fine by now. If issues persist, you can always call a pro and see what they recommend.