To Stick Or Not To Stick

January 26, 2011 9:04 PM

Why is a friends door sticking in dry weather and not wet?

At a friends house now. The door to her studio is sticking pretty bad. It works fine in wet weather. I thought the opposite would happen. What up?

posted by goalyeehah to home & garden (8 answers total)

Usually humidity causes things to expand. That means that if the door is made of something absorbent (wood, paper, cardboard-core), it can expand and jam/stick against the frame.

In this case, it is likely that something -- the door frame, a section of the wall, the underlayment of the flooring -- is pushed AWAY from the part of the door that is sticking, freeing it as (mysterious thing) is soaking up water.
posted by fake at 9:11 PM on January 26, 2011

If it's mid winter (no humidity, just frost) and everything shrinks, the frame shrinks too, or at least: can warp. Also, surrounding structures can set in a non-square fashion and make doors stick by offsetting them.
posted by Namlit at 12:01 AM on January 27, 2011

Happened to me, too. I kept taking the (heavy!) door off its hinges and planing a bit more off the bottom, but a couple of weeks later it was sticking again. Then a friend came to visit, took one look and said, that door's a parallelogram. He was right: its own weight was making it sag, and I hadn't noticed because it was happening so gradually. I got the local smith to run up a steel frame, jacked up the sagging side of the door (away from the hinges) and bolted the frame onto it. Problem solved. YMMV.
posted by aqsakal at 1:09 AM on January 27, 2011

It might be any of the above things. But my first thought, like fake, was that it could be the frame that's expanding when the weather is damp. Any expansion in the frame will tend to push the top of the frame up a little and make it slightly wider, particularly at the top. Depending on the materials used, the door may not expand as much as the frame.

The gap between door and frame needs to be enough to accommodate the door in wet weather, so it may still be a case of planing the edge of the door a little at the point where it sticks. But make sure everything is nice and square and that the door is solidly attached at the hinges and sitting properly in the frame, too.
posted by le morte de bea arthur at 2:15 AM on January 27, 2011

There's some misinformation here. When wood expands due to moisture, individual boards get wider and thicker but they do not get longer. When it shrinks, boards get narrower and thinner but they do not get shorter. The door frame can't shrink in a way that causes sticking. Neither does the opening get taller or wider in damp weather.

It would help to know whether this is an exterior or interior door, whether it's a slab or frame-and-panel door, whether it's a metal or wood door.

Has your friend been doing a lot of cooking or taking long showers? The weather -- is it hot and dry, or cold and dry? By "dry" do you mean "low humidity" or "not raining?" Even though absolute humidity levels are typically lower in cold weather, the relative humidity outdoors doesn't change much from winter to summer (except in coastal areas, where humidity is typically higher in winter). Condensation on the interior side of cold exterior doors can make the door damp even when indoor air is relatively dry.
posted by jon1270 at 4:14 AM on January 27, 2011

Longitudinal shrinkage of wood (pdf).
I'm not even claiming that this is the solution, I agree that we lack info here, but the option shouldn't be dismissed.
If the door itself is ply (and hence shrinks less) and the frame the typical medium-quality softwood, the here quoted 1/10 to 2/10 inch of shrinkage per 8 feet of length might just jam a door that's tight to begin with.
posted by Namlit at 6:35 AM on January 27, 2011

Oh man, now you're getting all technical. Yes, wood does shrink lengthwise a tiny, tiny bit as it dries out. As noted in that paper, the change is very small even over large changes in moisture content. Between fiber saturation (around 28% MC) and air-dry (~12%), the length of the board changes by about 0.1 - 0.2%. Within the range of oven dry to fiber saturation, movement is pretty much directly proportionate to the change in MC. Since the MC fluctuations in installed wood are never anywhere near so large (barring catastrophic roof leaks that would have the interior walls falling apart), the changes in length never approach the 0.1-0.2% described in that paper.

This part of the movement is not zero, but it may as well be.
posted by jon1270 at 6:56 AM on January 27, 2011

Are the hinge screws loose? Maybe the swelling of the wood around the hinge screws tightens them up in damp weather, making the door sag less. This would seem to apply primarily for doors that are usually closed.

Does it *always* free up in "dry" weather?

Finally, I'll restate what was mentioned above. If you're like me and use "dry weather" to mean summer, and "wet weather" to mean winter, then you've got it backwards when it comes to typical indoor conditions. Generally, the indoor humidity tends to be lower in the winter (central heating) than in the muggy summer, air conditioning notwithstanding.
posted by RikiTikiTavi at 4:01 PM on January 27, 2011