Exterior doors in St. Louis homes go through a lot. Humid summer air can swell wood and composite slabs, the air conditioner then runs in a sealed house, and winter heating dries everything out again. If a door sticks in July and rattles in January, the door and its threshold are usually reporting moisture and air leaks. This guide explains how to tell swelling from seal failure, what to check at the threshold, and what to do next.
Why doors change with the season
Wood and wood composite absorb moisture from humid air and release it when the air dries. A door that fits well in dry winter air can bind at the top corner during a muggy St. Louis week. Steel doors move less, but their frames and weatherstripping still shift with the house. The threshold, usually metal or wood with a strip of weatherstripping on top, is the lowest and most exposed part of the assembly. Rain blown against the bottom edge, water splashing off a step, or runoff pooling on a poorly graded landing can keep the threshold wet for days.
Signs the door is swelling
- The door binds on the latch side during humid weather but closes easily once the house is cooled.
- Paint or finish bubbles, cracks, or peels along the bottom rail or the edges.
- The door rubs the top of the frame or drags on the threshold.
- Dark spots or soft wood appear at the bottom rail, which can mean moisture is sitting in the wood rather than passing through it.
Signs the seal is failing
- Daylight shows around the edges when the entry lights are off.
- A draft moves across your feet, or you see fine dust lines on the floor just inside the door.
- Water stains or dark streaks show on the interior floor or trim below the door.
- Water pools on the outside threshold after rain, or the sweep is flattened, cracked, or missing.
Check the threshold and sweep first
Start at the bottom. Close the door, then slide a sheet of paper under the bottom edge at several spots along the length. If the paper slides out with no resistance at any spot, that gap is letting in air and rain. Look closely at the door sweep and the threshold seal. Replace a worn sweep with one sized for your door, and confirm the threshold sits flat and is fastened tightly. A loose threshold lets water work underneath it.
Look at the grading outside as well. In older St. Louis neighborhoods, a front stoop may slope toward the house, or a downspout may empty right beside the entry. Splash-back keeps the threshold wet. Correcting the slope or moving the downspout outlet away from the door often helps more than any change to the door itself.
Inside the house, follow the air
A door can look fine and still cause a humidity problem if air moves around it. In a sealed, air conditioned house, moist outdoor air can be pulled in through gaps at the threshold and jamb, then condense on cool surfaces near the entry. Place a simple hygrometer in the entry, away from the door itself, and compare its reading with a room farther inside. If the entry stays noticeably damper than the rest of the house, focus on the door gaps before blaming the air handling.
What to do next
- Note when the door sticks: after rain, during humid weeks, or only in winter. The pattern points to swelling or to a seal problem.
- Run the paper test at the bottom, along the latch side, and along the hinge side.
- Look for stains, soft wood, or bubbling finish on the bottom rail and threshold.
- Replace a worn sweep or threshold seal, and tighten any loose fasteners.
- Correct drainage at the step or move the downspout outlet so water runs away from the entry.
- If the wood is soft or dark, or the frame has moved out of square, have a qualified contractor look at the structure before you rebuild anything.
When to stop patching
Weatherstripping and sweep replacements are reasonable homeowner work and cost little time. Get a professional opinion if the jamb is rotting, the door will not latch once the weather turns dry, or water appears in the wall beside the frame. Those signs point to structural moisture, and a surface seal will not solve them. Keep notes on when the problem appears, take a few photos, and bring them to whoever inspects the entry. A clear record of the pattern usually makes the next step faster in any St. Louis home.