If you own an older home anywhere from Tinley Park to the city, you've probably watched thin lines open up between your floorboards in February, then vanish by July — sometimes replaced by board edges that lift slightly and catch the light. It looks like a flaw. It usually isn't.
At Landmark Flooring, we hear this question every single season. Solid hardwood is hygroscopic, meaning it constantly trades moisture with the air around it. Chicago air swings harder than almost anywhere, so your floor moves with it.
It's the Weather, Not a Defect
Wood never fully stops breathing after it's installed. When the air around it is humid, the planks absorb moisture and expand across their width. When the air dries out, they release that moisture and contract. This happens to every solid wood floor on earth — Chicagoland just pushes the extremes harder than most climates.
Our winters drop indoor relative humidity into the teens once the furnace runs nonstop, while July afternoons by the lake routinely push past 70%. That's a massive annual range for a natural material to ride out, and the visible result is seasonal gaps followed by seasonal tightness. None of it means your floor was installed wrong or milled poorly.
Winter Gaps Versus Summer Cupping
In winter, dry indoor air pulls moisture out of each board and the planks shrink, opening fine gaps along the seams. Lighter species like maple and white oak tend to show these lines more plainly than darker, heavily figured woods. In most cases the gaps close on their own once spring humidity returns.
Summer brings the opposite problem. As boards absorb moisture and swell, the pressure has nowhere to go and the edges rise higher than the centers — that's cupping. A little is normal and seasonal. Persistent, severe cupping usually points to a moisture source below the floor, such as a damp basement or crawl space, and that's worth investigating before it becomes permanent.
The Humidity Range That Keeps Wood Stable
The single most useful thing you can do is hold your indoor relative humidity steady through the year. Wood flooring is happiest in a fairly narrow band, and staying inside it dramatically reduces how far your boards travel each season.
Keep relative humidity between 35% and 55% year-round
Below 35%, expect shrinkage, gapping, and occasional splitting
Above 55%, expect swelling, tight boards, and cupping
Most solid hardwood lives comfortably at 6–9% moisture content indoors
How to Keep the Movement in Check
The most reliable fix is mechanical. Add an in-line humidifier to your forced-air furnace so the house holds moisture through the dry months, and run a basement dehumidifier in summer to keep ground moisture from migrating up into the subfloor. Together they flatten the annual swing your floor has to absorb.
Material choice matters too. If you're reflooring and the constant movement bothers you, engineered hardwood and wider-plank layouts behave very differently than narrow solid strip — and we'll walk you through which construction suits your room, your subfloor, and your tolerance for seasonal change.
Seasonal movement is manageable once you understand it, and the right floor for your home makes it nearly invisible. The team at Landmark Flooring has helped homeowners across Tinley Park, IL, Orland Park, IL, Naperville, IL, Oakbrook, IL, and Chicago, IL choose, install, and care for hardwood that holds up to Chicago's climate since 1991.
Stop by Tinley Park, IL to see solid and engineered options in person, feel the difference between species and finishes, and get straight answers about what will work in your space. Contact us today to book a visit or schedule an in-home measure.
