Technical guide 2 min read

Moisture & Humidity Standards

Wood moves with the air around it. What that means in a British home, what to measure, and how to keep a floor stable through the year.

Applies to

All wood floors

Main cause

Seasonal humidity swing

Measured with

Hygrometer and moisture meter

Most stable

Engineered construction

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Why wood moves at all

Timber is hygroscopic. It takes moisture out of the air when the air is damp and gives it back when the air is dry, and it changes size as it does so. This never stops. A wood floor is not a static object and was never sold as one.

In a British home the swing is predictable. Winter heating dries the air, boards give up moisture and shrink slightly, so fine gaps can appear at the joints. Summer brings the moisture back, the boards take it up and the gaps close. A floor that behaves this way is behaving correctly.

Good to know: Movement across the year is normal and is not a fault. What is not normal is cupping, lifting or a gap that never closes, and each of those has a cause worth finding.

Construction decides how much it moves

Two floors can look identical and behave completely differently, because what governs movement is how the board is built.

Solid wood

One piece of timber. Moves the most across its width, which is why it is not suitable for underfloor heating.

Engineered wood

A real oak wear layer over a cross layered core. The layers restrain each other, so the board holds its width. This is why it is approved for underfloor heating.

LVT

Not timber, so humidity does not affect it. It does respond to temperature, which is a different problem with a different answer.

What to measure, and when

Two instruments answer almost every question here, and neither is expensive.

Room humidity

A hygrometer on a shelf tells you what the floor is living in. Read it in January and again in July.

Subfloor moisture

A meter before fitting, taken in several places rather than one. Concrete and screed hold water long after they look dry.

After commissioning

Over underfloor heating, the reading that counts is the one taken after the system has been run and cooled, not before.

Near external walls

These are the coldest and often the dampest points in the room. Test there as well as in the middle.

Important: Where your product fitting instructions state a moisture figure, that figure governs. It differs by construction and by fitting method, and it is the number your guarantee is written against.

Keeping a room stable

You are not trying to hold the room at one number. You are trying to avoid violent changes.

Finish wet trades before fitting

Plaster, screed and paint all release water for weeks. A floor laid into that will move once the room dries out.

Let the packs settle in the room

Leave them flat and unopened where they will be fitted, for the period your fitting instructions state.

Heat gradually in autumn

Bringing a system up in stages over several days gives the boards time to follow. It is the sudden change that damages timber.

Ventilate rather than dry aggressively

A dehumidifier run hard in one room creates exactly the swing you are trying to avoid.

Watch conservatories and sun rooms

Wide temperature and humidity ranges make these the hardest rooms for any wood floor. Glue down performs better than floating here.

Worried about movement in your room?

Conservatories, new builds and rooms with underfloor heating each behave differently. Tell us the room and we will tell you what suits it.

Ask our team Subfloor requirements

Technical guide Subfloor Requirements Technical guide Underfloor Heating Guide Fitting guide Engineered Wood Installation Guide

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