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You Can’t Afford To Be Wet Behind The Ears

Rob Winstone on Equilibrium Moisture Content — Part 3

LAST month I explained how timber is affected by both relative humidity and temperature. We also have to consider the type of building that the material will be installed into.
BS 8201:2011 Code of practice for installation of wood and wood based panels says that the timber flooring should not be installed into a building until the environment is at the ‘in service’ levels and that the moisture content of the wood should be matched to that environment.
With the new Sustainable Code for building starting to be more widely used, our buildings will become more airtight with mechanical heat recovery systems removing humidity from wet airs and replacing it with warmer drier air.
There has been a shift over recent years to warmer environments and underfloor heating and as relative humidity falls with an increase in temperature, we can anticipate that during the heating season the timber will lose moisture and reduce in dimension.
The counter to this is that during the summer and into autumn when the heat system is off and the door and windows are open, we will continue to have the same high humidity’s we have had for centuries. Therefore the timber flooring will have to work between two greater dimensions.
But don’t forget that we still have a large aging building stock where the efficiency of the buildings are not so good and the relative humidity levels there may be generally higher.
We can use the emc of existing wood in existing building to help us. The timber that is there will be in equilibrium with that environment and therefore can tell us at what level of moisture content the new materials should be or what precautions are required to protect the new material from failure.
Wood flooring should be at the right moisture content to suit the environment that it to be installed into. BS8201 says that timber should be acclimatized for the least time necessary.
Remember that timber, through storage and transportation, can vary slightly in moisture content from one board to another and within the same length of wood flooring, Therefore the boards need to finally balance to the new environment.
For this to be achieved it is important that all of the boards surfaces are allowed to breathe to the rooms environment. It is therefore necessary for the boards to be stacked with spacing sticks, something that I have never witnessed on site.
This therefore makes knowing the product, your supplier and the conditions where it is to be used and in more detail so as to limit the amount of movement that will take place in the timber.
The Flooring Industry Training Association (FITA) run a one day course on ‘Moisture – preventing floor failures’ to help you understand moisture and using moisture testing meters.
The more you understand, the more you will test and the more you will understand the more successful you will be.

Rob Winstone is a flooring consultant, an expert witness for timber flooring and timber issues and an accredited civil and commercial mediator.
T: 07831 443088

This article has been reproduced from the Contract Flooring Journal website. You can find them at