By Mario Vilchis, owner, Vilchis Hardwood Floors. Working in Durham since 2009.
We get called in to fix other people’s hardwood at least a dozen times a year. About a third of those failures trace back to the same mistake: the floor went down before it had a chance to acclimate. By the time the homeowner notices, it’s January, the heat has been running for two months, and there are gaps between every other board wide enough to lose a crayon in.
This is the cheapest step in a hardwood install to get right, because the only thing it costs is patience. It’s also the step almost nobody respects.
What acclimation actually is
Wood comes off the kiln at the factory dried to a specific moisture content, usually 6 to 9 percent. That’s lower than the moisture content of the air inside most North Carolina houses. So when the boxes land at your house, the boards immediately start absorbing humidity. They get slightly wider. They get heavier. They keep doing that until they reach equilibrium with whatever your house’s interior is actually like.
Acclimation is the process of letting the wood reach equilibrium before it gets nailed down. Skip it and the wood acclimates anyway. It just does it underneath your finish, in the form of cupping, gaps, or buckling.
What the NWFA says about it
The NWFA’s installation guidelines are the industry standard. They cover acclimation in detail, but the two numbers most homeowners should care about are these. The flooring’s moisture content should be within 4 percent of the wood subfloor’s moisture content for boards under 3 inches wide, or within 2 percent for wider boards. The interior environment should sit between 60 and 80 degrees with relative humidity between 30 and 50 percent, and the HVAC should have been running at those conditions for at least 48 hours before the wood is even delivered.
Notice neither of those numbers is a number of days. That’s the trap. Most installers will tell a homeowner “we’ll let it sit for three days” or “five days.” Acclimation isn’t measured in days. It’s measured with a meter. The wood is acclimated when the meter says so, not when the calendar does.
Why the Triangle is harder than the manufacturer thinks
The kiln-dry target on a box of hardwood is calibrated for the average North American interior. The Triangle is not the average North American interior.
In July, indoor humidity in a Durham bungalow with the AC running can sit at 55 to 60 percent even with everything sealed up. Wood that’s “ready to install” off the truck isn’t ready for that. It needs to gain moisture and settle first. In January, with heat running, the same house can drop to 25 percent relative humidity, and the wood has to lose moisture before it goes down. Same house, same product, completely different acclimation timeline depending on the season.
A 1,000 square foot job in Hope Valley in mid-July might need 7 to 10 days. The same job in January might need 4 or 5. A house out near Lake Crabtree with crawl-space humidity bleeding up through the subfloor could need 14. We don’t know until we measure.
How we actually handle it
Mario is on every install, and the moisture meter is the first tool out of the truck.
Before the wood ships, we check the subfloor. Readings should be in the same ballpark as where the wood will eventually equalize. Concrete subfloors get a different test, either calcium chloride or RH-probe, depending on the situation. If the subfloor is too wet, we don’t deliver.
When the wood arrives, we open the boxes immediately. Cardboard traps moisture, which slows acclimation, not speeds it up. We stack the boards loose in the room where they’ll be installed, with spacers between them so air can circulate.
Then we wait. We come back every couple of days and pull readings off random boards from different parts of the stack. When the wood has equalized with the subfloor inside the NWFA’s window, we install. Sometimes that’s three days. Sometimes it’s two weeks. The number of days isn’t what we’re chasing. The number on the meter is.
A real example
Last spring a homeowner off Hillandale called us. Three houses down from a job we’d done a few years earlier. New install, different contractor, eighteen months old. Quarter-inch gaps every few feet across the whole living room.
I asked her if the installer had used a moisture meter before laying the floor. She wasn’t sure. I asked if the wood had sat in the house for any length of time before going down. She said the installer brought it in the morning of and told her the floor would “settle in” once they lived on it.
That’s the whole story right there. The wood was probably kiln-dried to around 7 percent. It went down in late August with the AC running at 55 percent humidity. By the time the heat kicked on in November, the boards had absorbed moisture, expanded against each other all summer, then contracted hard once the dry winter heat pulled it back out. Permanent gaps.
We fixed it, but fixing it meant pulling everything up and starting over. The job ended up costing her almost twice what doing it right the first time would have. Plus a week of being out of half her house.
Questions to ask the installer before you sign
A few things that’ll tell you whether you’re hiring somebody who knows what they’re doing.
Ask what kind of moisture meter they use and when they last calibrated it. Anybody who answers without thinking has used one recently. Anybody who fumbles the question hasn’t.
Ask what moisture content they’re targeting for your specific house, and how they arrived at the number. The right answer references the NWFA’s EMC tables, or a regional moisture chart, plus the season.
Ask how long they let the wood acclimate. The wrong answer is a number of days. The right answer is “until the meter readings stabilize.”
Ask whether they need the HVAC running at normal living temperature and humidity before delivery. If they don’t bring up HVAC at all, get another quote.
There are good hardwood installers across Durham and the Triangle who do all of this without being asked. There are plenty who don’t. The difference doesn’t show up on the estimate. It shows up six months later.
When hardwood is the wrong call anyway
Sometimes the house and the homeowner’s habits don’t match what wood needs. A vacation rental in Carrboro that flips between 90 percent humidity (no AC, doors propped open) and 40 percent (AC blasting for the next guest) every weekend is going to wreck a hardwood floor no matter how patiently it was acclimated. Same with a house where the HVAC runs inconsistently, or where there’s an unsealed crawl space pumping humidity up into the floor from below.
For those houses we usually steer people toward LVP or laminate. Both stay dimensionally stable in conditions that would tear up wood. I’d rather lose a hardwood sale than install a floor I know is going to fail.
What this comes down to
If you have a hardwood install coming up, three things matter more than almost anything else. Get the HVAC running at normal conditions a week before delivery. Make your installer take moisture readings on both the wood and the subfloor, and ask to see them. Don’t let the calendar drive the install date. If somebody wants to deliver Monday and install Wednesday in the middle of a humid Triangle July, push back.
If they push back at you for pushing back, you have your answer.
We work across Durham, Raleigh, Cary, and Chapel Hill. Call (919) 794-1116 or request a free in-home estimate, and we’ll come measure for real.
Mario Vilchis runs Vilchis Hardwood Floors out of 237 Obie Dr in Durham. He’s been installing and refinishing hardwood in the Triangle since 2009 and shows up to every estimate himself.
