BWF members such as yourselves frequently use our Member and Technical Helplines for assistance on a wide range of Employment, Health and Safety, Contractual and Technical issues. We’re putting up a frequently asked question every Tuesday in order to help members and illustrate the type of advice we are able to provide. If you have any questions that you would like to see featured, we would be happy to assist. This question and many others like it can be found in our Question Centre. If you want further advice on any of the issues, don’t hesitate to ring the helpline or browse our extensive publications library, which includes our documents on timber variety vs performance, care of timber windows on site, and resin exudation. This week: How can I control moisture content? Utilising timber with the correct moisture content for the intended end-use is probably the single most important factor in ensuring satisfactory long-term performance of wood-based products. It is also one of the least well understood by the specifiers of timber products.
Timber shrinks as it dries and swells again if wetted. If dried to a moisture content close to that which it will reach in service it will not swell or shrink significantly. Doors Timber used in the manufacturer of doors will be graded in accordance with BS EN 942:2007 Timber in joinery – General classification of timber quality and the workmanship will meet the requirements of BS 1186 Part 2:1988 Timber for and workmanship in joinery ‘Specification for workmanship’. The moisture content of timber in the doors should be in the range of 6% to 16% depending upon their type and location. Windows Windows should be checked at the time of delivery to ensure that they are in accordance with the order schedule, the delivery is complete and that each window, including any protective packaging, is not damaged.
For long term performance of the window and finish, it is important that this moisture content is maintained during storage on site and during the construction process. BS 644: Timber Windows recommends that the moisture content of timber windows should be between 13% and 19% although fully factory finished windows are likely to be manufactured at the lower end of this range. For further information on allowing for the movement of timber, please see this technical feature in ‘Join-in’.