Combating the Climate
The UK is seeing a bigger push for offsite methods than ever before, but our unpredictable climate can cause problems with build quality. Robin Lancashire, Timber Frame Consultant at BM TRADA, considers the challenges and solutions to mixing building innovations with wet weather.
Last year the NHBC published a report on modern methods of construction (MMC), which suggested that the majority of developers are now using innovative forms of construction, with much more being manufactured offsite. The drivers for using MMC are clear: increased efficiency and productivity, accelerated delivery, higher energy performance and improved quality.
With ever-increasing targets for housing, the Government is also putting pressure on developers to utilise offsite construction.
While the use of offsite methods – and specifically timber frame – is the solution to achieving energy efficient buildings with much shorter lead times, the realities and practicalities of this kind of building must be considered. On paper offsite is unbeatable, but how practical is it in the real world with our beloved British weather? As more homes are being built using offsite methods, we’re
receiving a significant rise in calls about the challenge of trapped moisture in timber frame buildings.
Previously, open panel timber frames were erected over a number of weeks, often getting damp from the rain in the process. The roof covering would then go on and the timber frame would begin to dry again, because it was well ventilated and any moisture absorbed into the timber frame materials was given time to escape. Only then did the insulation, polythene vapour control
layer and linings get installed in a dry environment. The timber would remain dry and deliver a good service life.
As an increasing number of components are arriving at site premanufactured, there is more to consider than just the timber frame – insulation, membranes and linings are also getting wet – and that can be very bad news indeed, particularly when a structural timber frame is in there too. If timber moisture content is above 20% for a prolonged period, it risks decay, and if a wet structure is enclosed with no ventilation, it also risks mould growth on surfaces.
If moisture damage occurs and drying out is needed, it counteracts the reasons for using offsite. Either the build programme is affected while the wet materials are dried or removed (which also increases costs) or the contractors plough on and hope for the best, negating the quality of the build and risking future structural failure if timber decay takes hold.
The solution is a tricky one. Developers are being encouraged to manufacture as much as possible offsite, yet the reality when the components arrive onsite can be challenging. It’s crucial that everyone onsite knows how these materials should be handled so that moisture stops being an issue for current and future buildings. Although achieving the solution may have its hurdles, the basic message is simple – arrive just in time, lift straight into final position and carefully protect onsite.