Why are there gaps between my floorboards?
Most gaps are wood shrinking in dry air: boards are always taking on or giving up moisture, so they narrow in winter heating season and swell back in humid summer. Check your indoor humidity first and keep it steady. Hairline seasonal gaps are normal; wide, uneven or growing gaps, or gaps with cupping or soft spots, point to moisture or movement below.
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By Kasra Taheri, Founder, LoclisPublished
Researched and drafted with AI, then checked claim by claim against the sources listed below before it was published. Prices and rules change; the dates beside each source say when it was last checked.
Step by step
Read when to stop and call a pro, further down this page, before you start.
Step 1: Measure the gaps
Slide a thin card or feeler gauge into several gaps and note the width and where they are worst, so you can tell later whether they are growing.
Step 2: Check the season and the humidity
Put a small hygrometer in the room. Gaps that open in winter and close in summer match the seasonal pattern.[1]
Step 3: Bring humidity into range
Aim for steady indoor humidity of 35 to 55 percent for hardwood, using a humidifier in the dry heating season and an air conditioner or dehumidifier in humid months.[2]
Step 4: Wait a full season
Let the floor go through a humid summer or a dry winter at steady humidity before you judge the gaps or fill anything, because many close on their own.
Step 5: Vacuum out the debris
Clear dust and grit from the gaps with a vacuum crevice tool so the boards can move freely and the dirt does not get ground into the finish.
Step 6: Fill only stable gaps
Once humidity has been steady, press a flexible wood-floor filler or a sliver of matching wood into the gaps that stay open, and wipe off the excess before it sets.
Step 7: Recheck at the next season change
Look again after the next big swing in weather; if gaps keep reopening or widen, move on to the pro list below.
Most gaps are seasonal shrinkage
Wood is never fully still. Dry wood undergoes small changes in dimension with normal changes in relative humidity.[1] More humid air will cause slight swelling, and drier air will cause slight shrinkage.[1] On a floor of many boards, a hair's width lost on each one adds up to visible lines between them.
That is why gaps often show up in January and fade by August. Changes that occur because of seasonal variation, although gradual, tend to be of more concern.[1] Virginia winters make it worse, because heating dries the air indoors. Shaw Floors notes: "Wood stoves and electric heat tend to create very dry conditions."[3]
Other causes worth ruling out
Seasonal movement is the usual cause, but not the only one.
- Wood installed too wet or too dry. The Forest Products Laboratory's Wood Handbook advises: "install wood at the moisture content levels that the wood will experience in service."[1] That limits later shrinkage and swelling. A floor laid straight from a damp delivery, without time to settle in the house, can shrink after the first heating season.
- Wide boards. A wider board moves more across its width than a narrow one, so its gaps are bigger.
- Age and wear. Old floors can shrink and loosen over decades, and nails or fasteners that worked loose let boards drift apart.
- Movement below. A flexing subfloor or a sagging joist can open seams along a line or in a patch.
Check the humidity first
A cheap hygrometer tells you what the room is doing. For hardwood, Shaw Floors advises: "maintain consistent humidity levels (35-55%) to prevent warping."[2] Virginia Cooperative Extension gives the same range for comfort: "people are most comfortable at 35% to 55% relative humidity."[4] For laminate, Shaw says to "maintain between 35% and 65% humidity year round to minimize expansion and contraction of your laminate flooring."[3]
In the heating season, "a humidifier can be used to prevent excess shrinkage due to low humidity levels."[3] In summer, "an air conditioner, dehumidifier, or periodically turning on your heating will help to maintain humidity during summer months."[3] Do not overshoot the other way. "Fungi (molds) grow in air over 60% relative humidity,"[4] so a humid house with a wet crawl space is a bigger problem than a gap.
Fix the gaps, in the right order
Fixing humidity comes before filling. If you pack a gap with filler in winter, the boards have nowhere to go when they swell in summer, and the filler pops out or pushes the boards into a ridge. Give the floor a full season at steady humidity, then fill what stays open.
For a stable gap, vacuum it clean, then press in a flexible wood-floor filler or a thin sliver of matching wood glued in place, and wipe off the excess right away. A wide gap in a few spots is a candidate for a sliver. Gaps through the whole room are usually better left alone or handled at the next refinish. For the cost and the repair-or-replace question, see how much floor repair costs in Virginia and should I repair or replace damaged flooring. Scuffs and scratches are a different fix: read how to fix scratches in hardwood floors.
Stop and call a pro if
- Gaps are wide, uneven or growing year over year, even when humidity is steady.
- Boards are cupped, crowned or lifting, which points to moisture rather than dry air.
- The floor feels soft, bouncy or sags near the gaps, which can mean a subfloor or joist problem.
- You smell must or see staining along the seams, or the gaps are near a tub, sink, dishwasher or exterior door. Find and stop the water first.
- The gaps are across a floor over a crawl space or basement that feels damp, because that moisture will keep moving the boards.
Getting help in Virginia
Loclis lists licensed Virginia contractors with their licence class. Browse flooring pros near you, or read more flooring answers.
When you are ready, describe the floor problem once and local pros quote it.
Common questions
- Are gaps between floorboards normal?
- Thin gaps that open in the dry heating season and close in humid weather are normal for solid wood. The Forest Products Laboratory notes that drier air causes slight shrinkage and more humid air slight swelling. Gaps that stay wide, keep growing or come with raised edges are not normal and need a closer look.
- Why do my floor gaps get bigger in winter?
- Heating dries the indoor air, and wood shrinks as it dries. Shaw Floors notes that wood stoves and electric heat tend to create very dry conditions. A humidifier in the heating season can limit the shrinkage.
- What humidity should I keep for a hardwood floor?
- Shaw Floors recommends consistent humidity of 35 to 55 percent for hardwood. For laminate, its range is 35 to 65 percent. Steadiness matters as much as the number, since the gaps come from swings.
- Should I fill gaps between floorboards?
- Only after humidity has been steady through a season. Filler locked into a gap in winter can be squeezed out or can push boards when the wood swells in summer. Many gaps close on their own, so filling too early often just repeats the work.
- Can gaps mean something is wrong underneath?
- Sometimes. Gaps that are wide, uneven, run in one area, or come with cupping, soft spots or a musty smell can point to moisture, a sagging joist or a failing subfloor. A flooring pro or carpenter can check from above and from the crawl space or basement.
Sources
- [1] Wood Handbook, Chapter 13: Drying and Control of Moisture Content and Dimensional Changes (FPL-GTR-190), USDA Forest Service, Forest Products Laboratory. Checked October 27, 2026.
- [2] Hardwood Care, Shaw Floors. Checked October 27, 2026.
- [3] Laminate Floor Care & Maintenance, Shaw Floors. Checked October 27, 2026.
- [4] ENERGY SERIES: What about Moisture? (2908-9020), Virginia Cooperative Extension, Virginia Tech. Checked October 27, 2026.
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