Cross Laminated Timber in Place of Cast in Situ Concrete Slabs

Mace installed 6000m2 of cross laminated timber (CLT) at Harwell NSTF in place of cast in situ concrete slabs.

Using this method had many benefits which are detailed below:

Sustainability:

• 36% carbon saving compared with a concrete frame (1,200 tCO2e for concrete and 770 tCO2e with CLT)
• No silica dust generated (air quality benefits)
• CLT can span further than composite metal decking (the obvious alternative), meaning that the number of steel elements was reduced
• Reduced embodied carbon

Health & safety:

• Installed with a guard rail as edge protection at ground level prior to lifting
• CLT has integral fire resistance properties
• Fully dry installation eliminating wet trade
• No hot works for shear stud installation
• Reduced weight allowed large sections of CLT to be placed reducing working at height – only limited by transportation size limits
• Panels shipped to site pre slung so reduced access to lorry required

Programme/Performance:

• CLT provided a 40% programme saving over the equivalent concrete floor slab
• MEP interfaces easily installed, and roof and floor finishes could be applied directly which allowed earlier watertight and fit out to commence.
• No temporary works or cure time for concrete
• CLT weight is ~6.0kN/m3 as opposed to 25kN/m3 for concrete (reduced foundation load) allowed change from piled foundation to ground beams
• Off-site manufacture and quality control
• Airtight due to lapped joint detailing
• Flat underside allows direct application of decorative finish

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