To install reclaimed oak floorboards, the room must have a relative humidity of 45 to 65 percent, at a temperature between 15 and 22 degrees Celsius. The wood itself must have a moisture content of 8 to 12 percent at the time of installation. If these conditions are not met, the wood will continue to move significantly after laying, resulting in gaps or warping. Below, the most frequently asked questions about moisture content, acclimatization, and underfloor heating are answered.
What moisture content should oak wood have before installation?
Oak wood is ready for installation when its moisture content is between 8 and 12 percent. For flooring applications in heated rooms, the lower end of this range is considered the most stable. Antique oak that has been stored outdoors or in a dry barn for years will in many cases have already reached this level without any additional drying step.
Freshly sawn or wet wood can have a moisture content of 30 percent or more. That difference may sound technical, but the effect is immediately visible: wood that is installed too wet will shrink and develop gaps. Wood that is too dry relative to its environment will swell. Due to years of natural drying, antique oak has a more stable cell structure than new wood — but even so, it requires the right conditions at the time of installation.
How dry does the room itself need to be for oak floorboards?
The room in which oak floorboards are to be laid must have a relative humidity of 45 to 65 percent. At a temperature between 15 and 22 degrees Celsius and a humidity level within this range, oak wood is at its equilibrium moisture content and will remain stable.
In practice, this means the room must be fully finished before installation begins. Fresh concrete floors, recently plastered walls, and newly applied render continue to release moisture for months. That moisture rises and is absorbed by the wood. A room that appears ready on paper may not yet be if the construction moisture has not fully evaporated.
- Concrete floors need a minimum of 3 to 6 months after pouring to dry sufficiently
- Anhydrite-based screeds dry differently from concrete screeds and require separate measurement
- Rooms without heating or ventilation dry considerably more slowly
- New construction structurally contains more construction moisture than renovation projects in existing buildings
What happens if the room is too humid or too dry?
A room that is too humid causes oak floorboards to absorb moisture and expand. This leads to warping, edges lifting, and in severe cases, damage to the joints between the boards. A room that is structurally too dry causes the opposite: the wood loses moisture, shrinks, and gaps appear.
Oak responds to changes in moisture. This is not a flaw, but a characteristic of the material. Due to its dense cell structure and long drying time, antique oak reacts less dramatically than younger wood — but it remains a living material that breathes. Extreme fluctuations in humidity, such as a room reaching 75 percent in summer and dropping to 30 percent in winter, are problematic for any wooden floor.
In practice, stable humidity is more important than the exact figure. A room that stays around 55 percent year-round is more favorable than one that fluctuates between 40 and 70 percent.
How do you determine whether a room is ready for wooden floorboards?
The room’s humidity is measured with a hygrometer. The moisture content of the floor construction itself is measured with a moisture meter for building materials. For a screed, the generally accepted maximum moisture content is 2 percent for cement-based screeds and 0.5 percent for anhydrite screeds.
- Measure the humidity in at least three locations in the room, preferably at different heights
- Measure the temperature at the same time, as humidity and temperature are inextricably linked
- Measure the moisture content of the screed using a CM test or a calibrated electrical moisture meter
- Repeat the measurements over several days, not just at a single point in time
- Verify that the heating system has been running for at least several weeks, especially in the case of underfloor heating
A single measurement provides only a snapshot. Anyone who wants to be certain that a room is sufficiently stable should take measurements at the same times each day for at least one week.
How long does oak wood need to acclimatize before installation?
In most cases, oak wood needs to acclimatize in the room where it will be installed for a minimum of two to four weeks before work begins. The exact duration depends on the difference between the wood’s moisture content upon arrival and the equilibrium moisture content of the room.
Acclimatizing means the wood is stored in the correct environment — not wrapped in packaging and not stacked without gaps between the boards. The planks need air circulation on all sides. If they are stacked tightly together or against a damp wall, they will acclimatize unevenly and subsequent measurements will not be reliable.
Antique oak that has been stored dry for many years generally requires a shorter acclimatization period than new wood. Even so, it is advisable to wait at least one week and measure the moisture content both before and after that period. Only once the readings are stable is the wood ready for installation.
Are there additional requirements when using underfloor heating beneath oak floorboards?
Underfloor heating imposes stricter requirements on both the moisture content of the wood and the conditions in the room. The maximum surface temperature of the floor must not exceed 27 degrees Celsius. In rooms with underfloor heating, humidity drops quickly in winter, placing additional stress on the wood.
Underfloor heating dries out the air. Combined with cold outdoor temperatures, the humidity in a heated room can fall below 35 percent. At that level, oak shrinks noticeably. For projects with underfloor heating, it is therefore advisable to run the heating system several weeks before installation, so that the screed is fully dry and the room has reached its operating temperature.
In addition, the underfloor heating must be started up gradually after installation. An immediate jump to the maximum temperature causes thermal stress in the wood. Increase the temperature in stages over a minimum of two weeks. Solid antique oak handles this better than thin engineered products, but the same principle applies here: gradual is the key.
How Frank Pouwer helps prepare oak floorboards for installation
Oak floorboards that are properly prepared from a technical standpoint will perform without issues for decades. It starts with choosing wood that is already dry, and with a supplier who understands what happens on site before the wood reaches you.
- Our antique oak has a natural drying time of more than five years, meaning that in most cases the moisture content at delivery already falls within the desired range
- We can measure and document the moisture content of the boards before shipping, so you know exactly what you are receiving
- We offer advice on the right board size, thickness, and finish in relation to the floor construction and heating system
- For projects with specific technical requirements, such as underfloor heating or large surface areas, we work with you to determine which boards will be the most stable
- Our stock of reclaimed wooden floors is extensive and well documented, allowing you to move quickly
Would you like to know which boards are available and whether they are suitable for your project? Request a quote and we will work together to find the best option for your situation.
