Moisture, Humidity and Room Climate
Wood moves with the air around it. What that means in a British home, what is normal and what is not, the readings the standards ask for before a floor goes down, and how to keep a room stable through the year.
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.
What the published standards say
Each entry is quoted from its source and linked to it. The full set is in the standards reference.
BS 8203 — relative humidity limit for a subfloor
UK practice following BS 8203 treats a subfloor as dry enough for resilient floor coverings when hygrometer readings do not exceed 75% relative humidity (65% RH for solid timber coverings), measured with a hygrometer sealed to the surface so that it reaches equilibrium with the base.
| RH limit, resilient floor coverings | 75 % RH |
|---|---|
| RH limit, solid timber floor coverings | 65 % RH |
“The base can be considered dry enough to install most floorcoverings if a series of tests produce readings not exceeding 75% R.H. (65% R.H. for solid timber floorcoverings).”
Source: F. Ball and Co. Ltd - Digital Hygrometer, Technical Data SheetRoom conditions at the time of fitting
The MMFA, the European association for multilayer modular floor coverings, requires the flooring to acclimatise for at least 48 hours in the same conditions as the installation area, stored flat and cross-stacked in unopened boxes at roughly 15-25 degrees Celsius and 35 to 65 per cent relative humidity.
| acclimatisation before installation | at least 48 h |
|---|---|
| storage and acclimatisation temperature | 15-25 °C |
| storage and acclimatisation relative humidity | 35-65 % |
“Leave the floor covering to acclimatise in the same environmental conditions as the installation area for a period of at least 48 hours prior to installation. Always store the boards flat and cross-stacked, in their original unopened boxes and at approx. 15-25 °C and between 35 % and maximum 65 % relative humidity.”
Source: Prior to installation — MMFA (Multilayer Modular Flooring Association)Acclimatisation before fitting
The Contract Flooring Association's guide states that the room should be at its in-service temperature 48 hours before installation so that the flooring can be kept in the room and reach room temperature before it is laid.
| conditioning before installation | 48 h |
|---|
“They also advise that this temperature should be attained 48 hours prior to the installation, so that floorings can be kept in the room and brought to room temperature (acclimatised) before installation.”
Source: CFA Guide to Contract Flooring - Contract Flooring AssociationMoisture content at delivery — what EN 13489 requires
EN 13489, the product standard for multi-layer parquet, requires the moisture content of the elements to be between 5 % and 9 % at the time of first delivery, measured by the oven-dry method of EN 13183-1. The corresponding figure for solid parquet under EN 13226 was not available from a source we could read, so it is not stated here.
| Moisture content at first delivery, multi-layer parquet (EN 13489:2023, clause 4.1.2) | 5-9 % |
|---|
“The moisture content shall be between 5 % and 9 % at the time of the first delivery of the product.”
Source: EN 13489:2023 - Wood-flooring and parquet - Multi-layer parquet elements (SIST preview of the standard, clause 4.1.2 Moisture content)How long a screed takes to dry
BS 8204-1 gives a drying allowance of one day per millimetre of thickness for the first 50 mm of a levelling screed, with longer per-millimetre times above that thickness, so a 50 mm screed drying in good conditions takes roughly two months.
| drying allowance, first 50 mm | 1 day per mm |
|---|---|
| thickness covered by the 1 day/mm rule | 50 mm |
| resulting drying time for a 50 mm screed, good conditions | about 2 months |
“with levelling screeds, one day should be allowed for each millimetre of thickness for the first 50 mm, followed by an increasing time for each millimetre above this thickness. It is therefore reasonable to expect a levelling screed 50 mm thick, drying under good conditions, to be sufficiently dry in about 2 months.”
Source: Drying of Screeds - RonacreteDamp-proof membrane — Approved Document C
Approved Document C, paragraph 4.2, states that floors next to the ground should resist the passage of ground moisture to the upper surface, not be damaged by moisture from the ground or by groundwater, and resist the passage of ground gases.
| paragraph in Approved Document C | 4.2 |
|---|---|
| requirement covered | C2 Resistance to moisture |
“Floors next to the ground should: a. resist the passage of ground moisture to the upper surface of the floor; b. not be damaged by moisture from the ground; c. not be damaged by groundwater; d. resist the passage of ground gases.”
Source: Approved Document C - Site preparation and resistance to contaminants and moisture, 2013 edition (HM Government)
