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Above left: The engineered or mass timber elements used for a New Model Building are glulam and LVL beams and columns, and CLT walls and floor slabs
Above right: The New Model Building uses a typical six-storey residential block to demonstrate how its principles and details can be applied
carbon structural material – at a time when the need to reduce carbon emissions and mitigate temperature rises has never been more urgent,” stated WTA. This loss of construction industry confidence, however, is not just being accepted. In fact WTA, working together with engineers Buro Happold, Gardiner & Theobald cost consultants and fire engineering specialists at UCL have just come up with a specific response. With backing from Built by Nature, an international network supporting initiatives to decarbonise the built environment, they have drawn up the New Model Building – a “set of design principles that showcase an exemplar methodology for building residential developments in a climate emergency”.
“Complying with current and consulted UK statutory guidance, the New Model Building utilises a low carbon engineered timber structure coupled with a non-combustible façade, demonstrating a way of building that responds to the challenge of meeting net zero carbon,” says WTA. “[It demonstrates] that timber can be used to construct housing that complies with statutory regulations and [aims] to change the current market perception of timber.”
The New Model Building uses a typical six- storey residential block to demonstrate how its principles and details can be applied. But it is stressed that they are not prescriptive and can be applied to deliver projects of varying forms and sizes and to produce bespoke designs for each site.
The engineered or mass timber elements used for a New Model Building are glulam and LVL beams and columns, and CLT walls and floor slabs. These can be used in a variety of ways and in combination with other traditional construction elements to deliver buildings that meet site requirements. At the same time, the New Model Building methodology has parameters. It has been developed for buildings under 18m high, with a floor-to-floor maximum of 2925mm, REI60 fire compartmentation and automatic fire sprinklers. Upfront embodied carbon (excluding sequestration) is 326kgCO2 m2
e/ (A1-5), and embodied carbon (A-C) is 271kgCO2
e/me, the RIBA 2030 Built Target. Buildings must also comply with all Building Regulation Approved Documents and not use combustible materials in external walls, allowing the building to achieve an EWS1 (external wall system) Form and meet GLA funding requirements.
The timber roof structure is installed to minimum 1:40 falls, with BROOF (t4) fire penetration resistant certified roof build up. The engineered timber structure is fully encapsulated using gypsum board applied in accordance with K-class test certifications and the façade is a non-combustible external wall system designed in accordance with Part B Regulation 7. Penetrations through the structure are protected using compliant details, balconies are of non-combustible steel structure in accordance with MHCLG and best practice methods of waterproofing are used.
The primary driver of the New Model Building, says WTA, is reduced carbon impact. Using an archetype residential building of six storeys and 29 flats, it completed a whole life carbon assessment (A-C), incorporating material volumes from the BIM Model and manufacturer Environmental Product Declarations and compared this to an equivalent building in concrete and steel frame. The carbon saving was 75%, plus the building achieved an A+ LETI rating (London Energy Transformation Initiative).
Other benefits of the New Model Building project is that it also comprises a set of details for key junctions. These are fully compliant with Building Regulations and, says WTA, will facilitate production of the technical design. “They have been developed in liaison with a national warranty provider to expedite the technical approval process,” it said. Comparing the archetype New Model Building with an equivalent reinforced concrete frame building using data from Q1 2023, it was 5% more expensive. But this figure does not take into account prelim cost benefits or cost savings through having a reduced build programme – and mass timber frames typically take a third of the time to erect of a concrete frame. Moreover, says WTA, building in timber is quieter and a mass timber prefabricated primary frame requires 60% fewer deliveries to site than a steel and concrete frame, “easing delivery times and construction planning”. ■
www.ttjonline.com | July/August 2023 | TTJ
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