‘Timber is one of the most common materials on a building site – but is often one of the least respected’. This is the conclusion argued by the Timber Research and Development Association (TRADA). In a recent article on the TRADA website, it was argued that poor storage and handling of wood on construction sites are some of the major causes of unnecessary damage.
The article further went on to say ‘Wood naturally contains moisture, the amount varying with the temperature and relative humidity of the surrounding air. Any mismatch between the moisture content of the wood and its surrounding environmental conditions can lead to changes in dimension as well as some physical and mechanical properties. All wood-based products, including external joinery products like timber windows, as well as solid wood, are subject to this change to some degree. It is particularly important when timber products are used in a centrally heated building.
Observing a few simple rules about the correct specification of moisture content and careful site storage can avert ‘drying out’ problems such as shrinkage, distortion and staining. In situations involving high class joinery or other prestige work, proper care takes on special significance.
It is desirable to introduce all timber and wood based products into the building at their in-service moisture content, but in practice this is rarely possible. However, if timber is ordered so that the recommended moisture contents are not exceeded at the time of installation, most shrinkage should not be a significant problem. For wood windows, this moisture content is between 12-19%. Creating and maintaining the correct site conditions is important for controlling moisture content.
Joinery and other wood products should be manufactured with the timber at the recommended moisture contents. If wood products have to be stored before delivery to site the manufacturer should keep them in conditions that will maintain the correct moisture content. Goods should be adequately protected during transit. This should ensure that they are delivered to site at the correct moisture content.
To avoid prolonged site storage and double handling, phase delivery to coincide with the progress of work. Use suitable handling methods to ensure that timber and wood products are not damaged during loading, transit and unloading.’
This essential advice from TRADA coincides with a new wood information sheet which is able to downloaded for free to TRADA members via their website.