St. Louis summers bring warm, moist air into the region, and winters bring dry indoor air once the furnace runs. Wood floors, interior doors and window trim respond to those swings more than most parts of a house. Wood takes up moisture from the air and gives it back, and it changes size as it does. Understanding that cycle helps you decide whether a sticking door is a humidity problem or something else.
How wood moves
Wood expands across the grain when it absorbs moisture and contracts when it dries. Along the grain it changes very little. That is why a solid oak floor can cup, gap or buckle, while a door can swell at its edges until it binds in the frame. Engineered flooring moves less but still responds, especially at seams and along the perimeter of a room.
What St. Louis seasons look like indoors
In late spring and summer, humid outside air can enter a house through gaps around windows, a damp crawlspace, a basement without a vapor barrier, or simply by running the air conditioner less than the weather calls for. Floors over a crawlspace or a basement slab often show changes first. In winter, heating dries indoor air quickly, and wood can shrink, leaving gaps between boards and narrowing the reveal around trim. Older homes in St. Louis and St. Louis County often have original oak floors and solid wood doors, so these changes tend to show up as seasonal patterns rather than one-time damage.
Signs to check
- Doors that stick in summer and swing freely in winter
- Gaps between floorboards in cold months that close in humid months
- Cupping, where board edges rise, or crowning, where the center lifts
- Trim pulling away from the wall or opening at the corner joints
- Dark or damp spots at the base of walls, under rugs or on exposed subfloor
- Finish that looks cloudy, blistered or lifted
Testing the air in your home
A basic hygrometer shows the relative humidity in a room and is widely available. Place one in the main living area, a bedroom and the basement, and read it over several days, including a hot, humid stretch and a cold, dry spell. A steady reading through the year matters more than hitting any single figure, and large swings are the bigger concern for wood. Keep a simple log so you can compare readings with the seasonal signs you see in the house.
Where the moisture comes from
Before blaming the air, check the sources. A dehumidifier running in a basement, a clothes dryer vented indoors, long showers without an exhaust fan, and a leaking crawlspace all add moisture. Ground moisture rising through a slab or crawlspace floor is a frequent source in older St. Louis homes. Gutters that discharge water against the foundation can feed the same problem, especially after heavy rain.
Practical steps for floors, doors and trim
- Confirm the source before acting. Read your hygrometer, check the crawlspace or basement floor, and look for leaks.
- Run exhaust fans in bathrooms and vent the clothes dryer to the outdoors.
- Keep gutters and downspouts directing water well away from the foundation.
- If readings stay high in a basement, use a dehumidifier and plan where its water will drain.
- Use a humidifier in winter only if the air becomes very dry, and watch windows for condensation.
- Do not trim a swollen door in the humid season. Wait until the air settles, since a door planed in July can leave a gap in January.
- Wipe spills promptly and use mats at entries to limit water carried in on shoes.
When to call a professional
Consider a flooring specialist or a licensed contractor if boards are cupped across a whole room, if the subfloor feels soft, if doors bind in both seasons, or if you see visible mold or notice a persistent musty smell. Those signs usually point to a moisture source that needs to be found and corrected before any cosmetic repair makes sense.
For a St. Louis home, the goal is steady conditions across the year, not perfect numbers. Track the air, fix the sources, and make adjustments only when the pattern is clear.