Symptoms
- Visible gap between the top of the baseboard and the wall
- Gap at the bottom between baseboard and flooring
- Gap size changes seasonally with humidity
Likely causes
- CommonWood baseboard shrinking with dry airSolid wood trim contracts in low humidity, opening small gaps at the wall.
- CommonUneven or bowed wall behind the baseboardA wall that isn't perfectly flat leaves the trim unable to sit flush everywhere.
- PossibleHouse settling shifting the floor or wall slightlyMinor structural movement over years can widen trim gaps.
What to do
- Measure the gap size to decide if caulk alone will bridge it or if trim needs adjusting.
- For small gaps, apply a bead of paintable caulk along the top of the baseboard.
- Smooth the caulk with a wet finger for a clean line.
- For larger gaps, consider adding quarter-round or shoe molding at the floor line.
- Nail the added molding into the baseboard, not the floor, so flooring can still move.
- Fill nail holes with wood filler and sand smooth.
- Paint or stain the trim and caulk to match.
Tools and parts
- Caulk gun
- Miter saw (if adding molding)
- Nail set
Paintable caulkSearch: “paintable caulk for trim”
Quarter round moldingSearch: “quarter round trim molding”
When to call a pro
Call a trim carpenter if gaps are large, uneven throughout the room, or if the wall itself needs to be addressed.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.