Every winter, Mario Vilchis fields the same nervous phone call. It usually comes from someone who recently bought an older Durham house with its original 1940s oak and has just noticed thin dark lines opening up between the boards. The caller wants to know what went wrong.
Usually nothing did. “In almost every case those gaps will close on their own by April,” says Vilchis, who has been laying and refinishing wood floors in Durham since 2009 and owns Vilchis Hardwood Floors, a family-run flooring company in the city. Seasonal movement, not damage or wear, is the most common reason homeowners call him back about a floor. “A hairline crack between boards looks like the floor is failing,” he says. “That’s just wood living in a Triangle climate.”
Why do hardwood floors gap in winter?
“Wood is never fully done being a tree,” Vilchis says. Years after a board has been milled and nailed down, it is still trading moisture with the air in the room, swelling a little when the house is humid and shrinking when it dries out. “It’s not a defect. It’s the material.”
What makes the Triangle hard on wood is the size of the swing. “We get sticky, soaking summers and dry, heated winters,” he says, “and that gap between the two seasons is wide.” Outdoor humidity here regularly tops 90 percent in August. Once the furnace comes on, the air inside the same house can drop below 25 percent, and by late February a home where nobody is managing humidity is often down around 22 to 28 percent.
The National Wood Flooring Association puts the safe zone for wood floors at 30 to 50 percent relative humidity, with the thermostat somewhere between 60 and 80 degrees. Vilchis says most Triangle houses blow through the top of that range every summer and the bottom of it every winter unless someone is actively managing it.
He has a number for how much a single board moves. A 5-inch plainsawn red oak board can change about 0.09 inches in width between 30 and 60 percent humidity. That is less than a tenth of an inch, but a living room floor has dozens of boards, and in January the shrinkage shows up as gaps between them.
How wide a gap is normal?
Vilchis sizes up gaps with things most people carry in a wallet. A winter gap about as thick as a business card is ordinary. “If those gaps close back up when summer humidity returns, they’re normal seasonal gapping and there’s nothing to fix,” he says. The National Wood Flooring Association’s guidance for homeowners says much the same: gaps that come and go with the seasons are considered normal.
A credit card is his other gauge. “If you have gaps wider than the thickness of a credit card and they’re still there by late May, that’s worth a call.” So is a winter gap getting close to an eighth of an inch. When gaps stay put, he says, the floor was usually installed too dry, or the house has a moisture problem that nobody has tracked down yet.
Why do older Durham homes see bigger swings?
A lot of Vilchis’s work is in Trinity Park, Watts-Hillandale and Forest Hills, neighborhoods full of houses from the 1910s through the 1950s that still have their original hardwood. Many of them sit on crawlspaces. “Whatever is going on under your floor is going on inside your floor too, just delayed by a few weeks,” he says.
He points to research from Advanced Energy in Raleigh that found traditional vented crawlspaces in the area stayed above 70 percent relative humidity all summer, while sealed, conditioned ones stayed below 60. He once pulled up cupped boards over a Durham crawlspace he describes as “basically a swamp under the joists,” and the floor was fine once the space underneath was fixed. “The floor was the symptom, not the problem.”
Sealing a crawlspace isn’t cheap. He puts encapsulation at $5,000 to $15,000 for most Triangle homes, “which is real money, but for older homes with persistent moisture issues it pays for itself in floor longevity alone.” For houses that can’t hold steady humidity at all, such as places that sit empty for stretches or homes where nobody wants to babysit a humidity gauge, he steers people toward engineered hardwood or luxury vinyl plank. “I’m not going to push solid hardwood on a house that’s going to fight it.”
What can homeowners do about winter gaps?
Buy a hygrometer first. They cost about $15 at a hardware store, and Vilchis wants one in the main living area and another next to any floor that has given trouble before. “If you don’t measure indoor humidity, you’re guessing,” he says.
Once the reading slips under 30 percent, it’s time to put moisture back into the air. A whole-house humidifier tied into the HVAC system does the most good, and Vilchis says one typically costs $400 to $1,200 installed. Portable units help too, though only in the room where they sit. He tells homeowners to aim for 35 to 40 percent through the winter.
Rugs and furniture parked over a heating vent are another culprit. The boards underneath dry out faster than the rest of the room, which is how one board ends up cupped or crowned while the floor around it looks fine. So is an uneven thermostat. North Carolina falls can bounce between 75-degree afternoons and 40-degree nights for weeks, and a house that gets heated hard at night and shut off during the day dries the top of the boards while the underside stays damp from the crawlspace. Vilchis calls that a recipe for early gaps and light cupping.
He would also rather people trust the gauge than the calendar. He has seen homeowners run a dehumidifier and a humidifier at the same time without realizing it. In Durham, the dehumidifier can usually come off around mid-October, once highs settle into the 60s, and the humidifier around mid-April, when they reach the 70s. “The right humidifier and the right hygrometer will do more for your floors than any product I could sell you,” he says.
When does a gap point to a bad installation?
Gaps that never close are a different story, and Vilchis says many of them trace back to the day the floor went down. About a third of the failed hardwood floors he is asked to repair come down to skipped acclimation, the step where the wood sits in the house and adjusts to its humidity before anyone nails it down. “This is the cheapest step in a hardwood install to get right, because the only thing it costs is patience,” he says. “It’s also the step almost nobody respects.”
Wood leaves the kiln at roughly 6 to 9 percent moisture content, drier than conditions inside most North Carolina homes. Skip acclimation, he says, “and the wood acclimates anyway. It just does it underneath your finish.”
He remembers a call from a homeowner off Hillandale whose floor was 18 months old and had quarter-inch gaps every few feet across the living room. Vilchis asked whether the installer had used a moisture meter before laying it. She wasn’t sure. He asked whether the wood had sat in the house for any length of time first. It hadn’t: the installer brought it in the morning of the job and told her the floor would “settle in” once they lived on it. “That’s the whole story right there,” Vilchis says. The floor went down in late August with the air conditioning holding the house near 55 percent humidity, swelled through the rest of the summer and shrank hard once the heat came on in November. Fixing it meant tearing out the floor and starting over, at nearly twice the cost of doing it right the first time, plus a week out of half her house.
Anyone hiring a flooring company in Durham can screen for this before signing. Vilchis suggests starting with the meter: what kind the installer uses, and when it was last calibrated. “Anybody who answers without thinking has used one recently,” he says. “Anybody who fumbles the question hasn’t.” Next comes the moisture content they’re targeting for your house and how they got to that number. A good answer refers to the NWFA’s moisture tables and the time of year. Then ask how long the wood will acclimate. “The wrong answer is a number of days,” he says. “The right answer is ‘until the meter readings stabilize.’” If an installer never brings up running the heat or air conditioning at normal settings before delivery, he says, get another quote.
Is winter a bad time to install or refinish hardwood?
Not if the installer goes by the meter. The season changes how long acclimation takes: a 1,000-square-foot job in Hope Valley might need 7 to 10 days in mid-July and only 4 or 5 in January. The month Vilchis is wary of is December, and only for people who need the floor finished before a holiday. “Not because the floor will fail,” he says. “Because the margin gets thin and something usually slips.”
He calls winter “quietly one of the better times to refinish,” since dry indoor air shortens the wait between finish coats. The catch is that a closed-up winter house is hard to air out. If someone at home has asthma, or there’s a baby in the house, he says to tell the contractor up front so they can choose the finish with that in mind.
What should homeowners watch for in spring?
For most winter gaps, the fix is patience. “A wood floor that moves a little with the seasons is doing exactly what wood does,” Vilchis says. What he does want people to call about are gaps wider than an eighth of an inch that are still open in spring, cupping that hasn’t flattened back out by November, and dark stains that won’t lift with normal cleaning, which can mean moisture has gotten under the finish.
