Wood and Weather
We all know that weather affects wood outdoors. Sometimes the effect is even desirable, as weather grays wood and makes it look old.
But weather affects indoor wood as well. Wood, of course, was once a tree, a living thing. It is composed of cells of various types. While the wood in a cabinet may not be sprouting any new life, those cells still collect water when in a humid environment and get rid of water when the environment is dry (such as in the winter when the furnace is on).
If you bought, for example, a hand-made cabinet in January and the door fit perfectly in its opening, don’t be surprised in July if the door has gotten a little big for the opening. Those cells filled up with the water in the air.
There are ways to get around this. One way is to use plywood or medium density fiber board (MDF), particularly in areas where these materials will not be seen, such as interior shelves, the back, the bottom, and so forth. Plywood is wood but because the grain of the thin layers of wood run perpendicular from layer to layer, moisture will affect it much less. MDF is made up of wood product ground up very fine (not like particle board where a broken piece looks like compressed oatmeal; MDF is very strong and smooth) with an inert glue. While the surface of MDF will swell if exposed to a puddle of water, moisture in the air does not affect MDF.
There are also some tricks to building that allow for the wood to change from season to season. For example, carpenters typically do not attach a whole wood table top to a set of table legs. To do so is an invitation for the wood to form a large crack. Instead, the table top is held on by a clip (metal or wood) set in a groove in the apron and screwed to the underside of the top. The groove allows the wood to move back and forth without cracking.
Likewise, carpenters usually allow panels in doors to “float”–they are not glued or otherwise fastened in the frame of rails and styles. Finally, if a carpenter needs a wide board and glues up several smaller boards to achieve this, he or she will make sure that the growth circles are opposite from one board to another. If the rings in the end look like smiles on one board, they flip the next board so the rings look like frowns.
If you want to make sure a door will fit year round, buy the cabinet in the summer or buy one in the winter that has a little bit of space between the door and the frame. The charm of wood is its variability in terms of grain and feel. Moisture is just one more area of variability.