Equilibrium for Wood Moisture Content
Wood has been used as a building material for centuries, and over that time, we’ve learned a lot about what it takes for wood to keep both its beauty and its durability.
For most wood products, the most important requirement is that “green,” or freshly cut, wood has to be dried before it can be used effectively. Drying makes final dimensions more predictable and the wood easier to work with. It also increases wood’s strength, helps it bond better with adhesives, and lowers its weight for shipping, storage, and handling.
Over-drying, on the other hand, can lead to splits, cracks, warping, and other defects that affect the wood’s machining, safety, value, and appearance.
For any wood product or project, there’s an ideal moisture level that lets the wood machine well, perform well, and keep its natural beauty. But that level isn’t one fixed number. It depends on the temperature and humidity where the wood will be used, which is why tools like our EMC calculator and an accurate moisture meter are so useful.
Wood’s Natural Balance
Like many natural materials, wood is hygroscopic: it naturally absorbs moisture from the air around it and releases moisture into it. Even after green lumber is dried, the wood’s cells keep taking in moisture when the surrounding air is humid and giving it off when the air is dry. So the amount of moisture in any piece of wood depends largely on the conditions around it, mainly the relative humidity (RH) and temperature of the air.
In uncontrolled environments, these changes can be damaging, because they can cause rapid or extreme shifts in the wood’s moisture content (MC). As wood absorbs or releases moisture, not only does its MC change, but so do its dimensions. Cracks, splits, finish failures, warping, cupping, crowning, gaps, or adhesive failures can result if the changes happen too fast for the wood to gradually reach a balance with the air around it. Different species also tolerate moisture changes differently because of their structure.
All wood needs to reach a balance with its environment to prevent moisture-related damage. That balance is called equilibrium moisture content, or EMC. Wood flooring, furniture, and every other wood product need to reach an MC that’s in balance with the humidity and temperature around them.
How Can You Help Wood Flooring Reach Equilibrium?
1. Schedule delivery after the job site is at service conditions.
Even nearby plaster or masonry that hasn’t dried can temporarily affect the MC of wood flooring. Make sure the flooring has time to reach equilibrium with the job site’s conditions before installation, and ideally, install only once the space is at normal living conditions.
2. Make sure subfloors are dry enough.
Subfloors, especially in new construction, can still hold a lot of moisture. Concrete should be at the specified RH level (relative humidity testing is the most accurate way to measure moisture in concrete). Wood subfloors should be checked with an accurate wood moisture meter to make sure the flooring and subfloor MC are close enough. National Wood Flooring Association guidelines call for the flooring to be within 4 percentage points of the subfloor for strip flooring (under 3 inches wide), or within 2 points for plank flooring (3 inches or wider). If they aren’t, allow more time to reach equilibrium. You may also be able to use a moisture mitigation product, such as a vapor retarder, before installing the wood flooring.
3. Allow time for the flooring to acclimate.
Always follow the flooring manufacturer’s acclimation recommendations for its products.
After delivery, open the packaged flooring and separate it as much as possible so air can reach all the pieces and the whole load can acclimate. Take an initial reading with an accurate wood moisture meter so you can track how the MC changes over the following hours and days. Wagner Meters’ pinless wood moisture meters let you take as many readings as you need, as often as you need, without damaging the flooring.
4. Install and finish.
Careful installation is also part of keeping a wood floor beautiful, and once the flooring’s MC is in balance with the job site, you can proceed with confidence. The finish helps slow moisture movement at the surface, but be sure to give your customers maintenance advice so they can spot changes that might signal a moisture problem.
Free Download – 4 Reasons Your Hardwood Flooring Failed
Wood Moisture Content and EMC
Even in a fairly stable environment, wood still moves with the seasons as humidity and temperature change. Indoor heating and air conditioning help limit those changes, but small ones still happen, like a door that sticks in humid summer weather, or small gaps between floorboards in dry winter months.
Letting the flooring reach equilibrium before installation and verifying its MC with an accurate wood moisture meter are the best ways to get a beautiful, durable wood floor.
Troy Edwards is Technical Service Supervisor for Wagner Meters, Inc., where he oversees manufacturing, quality control and IT service for their electronic measurement products for the building and construction industry. Troy holds an AAS in Electronics Technology and has over 20 years’ experience in various electronic manufacturing and production positions.
Last updated on October 12th, 2026
800-634-9961
