The timber at our 55 Pall Mall development, an 8-storey speculative office building, is cross-laminated timber (CLT) used for the floor slabs. These are supported by a steel frame, with a high recycled content, forming a hybrid structure. The use of CLT has been popular in Scandinavia, as well as mainland Europe for many years, and is now growing in popularity here in the UK too. On these shores it’s most often used for smaller residential blocks, extensions to existing offices, as well as schools, doctors’ surgeries and other public buildings – all sharing the common attribute of being just a couple of stories high, where the speed of erection is a big draw.
Mass timber for taller buildings has historically been more challenging here, facing a stringent post-Grenfell regulatory environment and also nervousness from the insurance industry. This is changing though. Excellent work by bodies such as the Structural Timber Association, The Alliance for Sustainable Building Products, Built by Nature and others has started to dismantle many of the hurdles, both real and perceived. As a result, there is a growing recognition that mass timber offers an exciting and relevant material with which to build new mid-rise commercial buildings.
For many the main argument for timber is an aesthetic one, but exposed timber, to some eyes can have a slightly rustic or domestic aesthetic. Full credit to our friends at Berkeley Estate Asset Management for delivering the first timber building in Mayfair, 36-38 Berkeley Square, a huge success, attracting leading fashion brand Chanel to choose it as their global headquarters. However, we know that a fair amount of the exposed timber is in the process of being covered up by the tenant’s fit-out.
Similarly at The Carter of LVL (Laminated Veneer Lumber) on the top floor extension has been largely covered by the tenant.
This is because there are a multitude of other very strong reasons to use timber in our new building, beyond the visual aspect:
Low carbon – it sounds obvious, but the carbon savings can be very substantial. Our embodied carbon measure for the whole building is 499 kgCO2/m2 (A1-A5, excl. biogenic carbon, Stage 5, RICS v2), which is extremely impressive by any standards for a new building (with an element of retained façade and basement). This is 47% below the GLA Benchmark and 17% below the GLA Aspirational target.
Lightweight - this means the new building, despite being larger than the previous one, is actually lighter. This in turn means we were able to re-use the existing piled foundations and basement construction. This saved an enormous amount of carbon, as well as programme time and cost. It also meant less risk in dealing with the London Underground tunnel underneath us.
Spatially efficient – we were keen to use a chilled ceiling environmental control system for comfort and for low energy reasons. CLT provides the perfect flat soffit for this, and coupled with fresh air under the floor, means we were able to squeeze the total floor/slab depth (underside of soffit to top of floor tile above) to just 750mm, which includes a 275mm clear floor void. This allowed us to maximise the clear ceiling height on the floors to over 2,800mm.
Clean, fast erection – there’s far less dust and noise associated with CLT slabs, with full strength being achieved from the moment it’s dropped into place.
Future flexibility – our CLT panels, 5.4m x 2.2m, can be removed should, for example, a communication stair between floors be desired.
