CLT – the optimum medium rise solution

Greg Cooper, engineering manager for the X-LAM Alliance highlights the benefits of using cross laminated timber as a core structural component for residential applications:

CLT is now extensively used across the commercial and education construction sectors and the benefits have been widely acknowledged, but it has not been prolifically used in residential developments in the UK until now. According to the findings of a recent survey by the Structural Timber

Association, 74 per cent of the UK’s contractors, developers, architects and registered providers revealed they plan to increase specifications of structural timber due to benefits such as thermal, acoustic and sustainability performance, together with speed of build.

It is in medium rise residential developments where the advantages of CLT as a core structural solution truly come into play. The key is in the strength to weight ratio of the engineered timber – it has proven multi-storey capability, with residential buildings up to nine storeys already constructed in the UK and a structural capacity beyond this. Typically the solid timber walls for five to six-storey construction are in the region of 140mm thick, therefore optimising internal space. Factory manufactured to exacting standards, CLT is an extremely stable solution which has little shrinkage or movement post construction.

The benefits during construction are numerous – from reduced loading on foundations and infrastructure services, to impressive thermal, acoustic and airtightness performance over more traditional materials, but most importantly a CLT construction solution provides cost and programme certainty.

Cost and programme certainty

Being a largely prefabricated off-site solution, CLT is manufactured to exceptional levels of accuracy, ensuring minimal defects. This improves construction and project delivery timescales, reduces costs and maximises efficiency on all levels.

With other methods of construction, significant contingencies have to be allocated for unpredicted situations, such as secondary members for additional structural bracing. With cost certainty crucial for developers and affordable housing providers, CLT eliminates this risk as it is manufactured in controlled factory conditions and the only elements which may affect costs are changes to the design of the structural frame or building reconfiguration.

Speed and sustainability

Precision engineered for on-site installation, using CLT as a core structural component reduces site construction time, making project planning less weather-dependant, more predictable and reduces programme risk. Internal works can proceed earlier to make the critical path run more smoothly, which again improves construction and project delivery time, reduces costs, maximises efficiency on all levels, and most importantly offers a faster return on investment.

Timber is the number one renewable, mainstream construction material and can produce greener buildings with a lower carbon footprint. With sustainability in the construction industry being of high importance, having PEFC or FSC Chain of Custody Certification ensures projects maintain a fully transparent Green Supply Chain.

Fire resistance

One of the most crucial advantages of particular relevance to multi-storey residential developments is CLT’s inherent fire resistance. The panels can be designed to a specified fire resistance and unlike steel, remain structurally stable when subjected to high temperatures. CLT panels can be designed to fire resistances of 30, 60 and 90 minutes.

CLT is the only structural timber solution to fully comply with all Fire Resistance REI classes and addresses all three (loadbearing capacity, integrity and insulation performance requirements) without the need for costly add-ons or adaptations.

The optimum medium rise solution

With the housing shortfall making the headlines on a regular basis and the 2013 Offsite Housing Review highlighting the potential for off-site construction methods to play a more significant role in the housebuilding industry, the housing sector is increasingly turning to cross laminated timber as the optimum sustainable solution for medium rise housing, particularly in highly populated, urban areas.

At the forefront of European CLT research and development, the X-LAM Alliance is an innovative partnership bringing to the UK construction market a seamless and consistent method of supplying certified structural packages, across all construction sectors.