A special NLA Think Tank with experts from the field sought to find some answers – unearthing in the process that there are moves afoot to self-insure buildings, hitherto a major stumbling block in creating tall timber structures.
That point came from Louisa Bowles, head of sustainability at Hawkins/Brown, who said that there is an initiative going on within the industry about developing self-led insurance schemes for developers or contractors who want to work with timber. ‘It will be interesting to see where that goes’, she said, ‘if that’s a potential solution to some of those insurance barriers, which I’m sure all of us have probably faced at one time or another on these schemes’.
The event began with a presentation on the challenges around environmental design targets associated from tall buildings from Wilkinson Eyre director Dominic Bettison, also of NLA’s Tall Buildings expert panel, much of it informed by a City of London tower the practice is designing for Aviva. Right from the get-go, the client wanted an ‘incredibly low carbon building’ as an aspiration, he said, and towards the industry goal of getting operational energy down by 75% and embodied carbon down by 75% across all building typologies by 2030. With tall buildings that is more challenging, not least because of things like passenger lifts but also in cooling and in structure, including in creating large basements - which ‘seem to be getting deeper and bigger to allow for more plant and bicycle storage, ironically’. But tall buildings can be a sustainable form since they play a role in helping cities reach governmental targets for densification; can reduce urban sprawl; give a long design life that should allow for refurbishment and re-use and longer life means a stronger case that timber is genuinely sequestered. ‘We think there really is an opportunity here to capture carbon for long periods of time’, said Bettison. Tall buildings tend to have smaller roof areas, but PVs are increasingly being integrated into facades, he added, while things like battery storage of energy are also increasingly an option, but there is a negative perception among the general public that tall buildings are gas guzzlers, which needs to be overturned.
Fred Pilbrow, senior partner of Pilbrow and Partners, showed the practice’s work for Dutch developer Edge Technologies on a new 28 storey office tower and new public park and garden – an important aspect of tall buildings to allow for more generous public space. The scheme’s embodied carbon capability is also interesting since it is a hybrid structure of post-tensioned concrete for the superstructure and the use of highly flexible CLT, the project aiming at BREEAM Outstanding and Well Platinum. The base of the side-core building is a four-storey cluster of timber mezzanines with exposed post-tensioned concrete slab on the upper floors providing good thermal conditions. The compartmentation is also good for fire prevention, Pilbrow added, while other green features include an intelligent chilled ceiling system (including occupational sensors), photovoltaics, heat pumps, all of which yield a 51% reduction in current Part L and embodied carbon of 704kg/m2 with a ‘route map’ to get down to around 540. The scheme also includes a collaboration idea with Tesla to install a battery pack and enable it to get to carbon positive status in use.
In the end we want these buildings to be adaptable and long life. That’s probably the most important thing we can do in terms of justifying the initial carbon investment in the system.
Rory Bergin, Sustainable Futures Partner, HTA said the practice was moving more towards prefabrication in some of the residential schemes it designs, with initial figures showing 20-40% reduction in embodied carbon, even without using timber and mostly taking in situ concrete out of the process, replacing it with steel. ‘The impact of that is huge’.
Russell Whitehead, Director, Robert Bird Group, said there was still a drive to build in timber because it was perceived to be the most sustainable solution, but there was also a move towards people combining more appropriate solutions to still meet flexibility and the brief office tenants expect to see, especially in central London. But it was ‘a shame’ that timber was not possible to be used as a building material in taller buildings because of the perception from insurers and mortgage lenders, not least because it tends to be concealed. ‘I guess it's going to take a while to get over the impact of Grenfell intelligently understand how to get around those issues and get confidence back in the construction industry that we are able to deliver high quality buildings that are built as per safe details’.
Think tank chair Peter Murray said timber use in Britain had been a problem since 1666 and the Great Fire of London, and was latterly very impacted by Grenfell Tower. In Australia, though, said Philip Vivian, Director, Bates Smart the effects of Grenfell were mostly felt in composite aluminium and cladding but they had less of an issue convincing fire departments over timber use.
In the US, meanwhile, said David Crabtree, Practice Leader and Design Leader, Perkins & Will there was more ‘acceptability’ with large municipalities considering mass timber, not least because of the precedent of lower-rise timber buildings and examples from China. But does everything have to be high rise in the ’10-mile city’, he asked, with its ‘comfortable density’ and more mid-rise?
Commercial seems to be more open to timber than residential, added Bowles, and work is underway on establishing new embodied carbon targets to ‘bring together all the conflicting ones across the industry at the moment’, using ‘more robust data sets’ in a bid to align them more fully. But the London Fire Brigade is following a ‘very, very tough line’ on all aspects of regulations on schemes over 18m, even without CLT, said John Robertson of John Robertson Architects, in the aftermath of Grenfell. Testing seems to be the area where there is least data, he added. ‘There is obviously a lot of data around on using CLT, it’s just getting it into some sort of regulatory format would be really good. It would almost be the breakthrough that we all need’.