Wooden and wooden frame doors are affected by humidity, humidity fluctuations, or excess moisture, as well as the temperature differential between the two sides (thermal bowing) .
Typical examples, when a door may be susceptible to bowing because of local water or humidity exposure, include:
- The door leaf was trimmed and the raw wood was exposed - this will increase the tendency of the door to respond to humidity.
- The bottom of the door comes into contact with a wet floor.
- A high level of humidity from the shower causes water condensation on the door panel. Water drops on the edges of the door panel or around the hardware will find their way to the wood frame.
Understand temperature differentials
It is common for wooden doors to respond to the temperature differential between two sides (such as house-to-cellar/garage/attic doors). Most garages are not tempered and tend to be colder in the winter and quite warm in the summer. Conversely, most houses stay heated or cooled within a relatively narrow temperature band. A wooden door may bend toward the warmer side, away from the cold area.
Each door vendor has specific technical standards: Dorsis uses wood material with a moisture content (MC) of about 12% for areas with roughly 40-60% relative humidity (RH). When the door gets exposed to higher humidity, the moisture content may climb to about 15-17% over several months. The higher MC may cause the wood frame to swell, causing the door to bow. Likewise, the wood may shrink and deform the door in a dry environment.
How to adjust a bowed (warped) door
WARNING: There's a limit to how much you can adjust the door using the built-in door straightener — the straightener may not allow you to remove more than 2.5 mm (up to ~3/32") from the bow. Do not overtighten the straightener: applying excessive force may cause the door frame to break, resulting in permanent damage to the door.
- Set two sawhorses at a distance roughly equal to the door panel's height.
- Place the door leaf on two sawhorses so the bow is on top. The weight of the panel will help straighten the door.
- Find a square opening for the straightener at the top edge of the panel. The straightener is on the "lock side" of the door, about 10 cm (~4") away from the edge. A round white sticker may cover the hole. If the door is a wood veneer door, veneer may cover the hole — use a small needle to find the opening.
- You'll need a 5 mm metric Allen Hex Key (or hex bit) at least 4" long to reach the straightener.
- Place a long box-beam level on the door panel (Stabila, Sola, or similar.)
- Turn the Allen hex key 90° in one direction (you may need to try both) and observe if the door panel adjusts in the desired direction. Use the box-beam level to asses progress. Work in 90° turn increments. Once you feel that you need to apply significant rotational force (torque), stop. You are likely at the maximum tension you can use before damaging the panel.
- Leave the door on the sawhorses for 24 hours. After 24 hours, check if you can re-adjust the straightener (try a 90° turn).
