Several design options were created, all adhering to the above principle elements, which were evaluated from the perspective of both cost and carbon reduction. “The client opted for a bowstring truss solution using glulam beams supported by the external columns, a timber-framed office and for all the secondary elements to be in timber,” continues Hagan. “We developed the concept design for this to Stage 3, passing it on to a Specialist Subcontractor (B & K Structures) for the detail design and construction stages. During the design process we worked closely with B & K Structures to inform ASI on likely cost and programme implications of our design proposals”
The environmental team modelled all the options, including the original steel design (the baseline model), and the net effect of adopting the chosen solution was a 30% cut of life carbon. From a baseline of c.1700 tonnes of carbon, the design modifications resulted in a saving of 500 tonnes.
“We could have saved even more carbon if we had been able to replace the steel cladding with a more sustainable option, but this was not possible since planning consent had already been granted and construction was imminent,” Hagan concludes. “Although our solution was more expensive than the baseline model, the client considered the carbon savings outweighed the cost. In future, with involvement from the start, we will be able to design the most efficient timber frame building; and if the warehouse were to be let before construction, we could assist the client further by offering a range of designs for tenants to select according to their different requirements.”