PRACTICE
BUILDING COST MODEL: RESIDENTIAL TIMBER

We really enjoyed collaborating with Alinea on the Building cost model article about the use of structural timber in residential developments.  

The study which compared two detailed cost models, one each for a CLT and concrete design for a seven-storey private residential building. The scheme was designed with both a timber and concrete solution in mind at the outset, with a structural layout to suit both.

The outcome of the analysis showed that 'the construction cost variance between timber and concrete for this hypothetical scheme is minimal. The higher CLT superstructure costs are offset by the ability to reduce pile quantities because of a lighter frame, hence a saving on substructure. The CLT programme for the frame and upper floors is around 10–15% shorter than the concrete option, resulting in a lower preliminaries cost.

With the quicker frame programme and virtual parity in construction costs the overall appraisal figure with CLT should glean a greater return, with units coming to market quicker than the equivalent RC scheme. Further potential savings could arise from the ability to reduce floor-to-floor heights (CLT floors are thinner than the concrete equivalent), which brings savings not only in frame costs but more significantly in external walls.

Exposing walls and soffits of slabs could also benefit costs and programme, but this would depend particularly upon input from fire and acoustic specialists to ensure a fair comparison.

Concrete is the most prevalent frame material both historically and currently for new-build residential developments. Aside from its inherent design qualities, the costs associated with low/mid-rise residential are in the main more competitive than alternative materials. The scale of competition in the concrete market helps to keep costs competitive, meaning that pricing levels are subject to a high degree of variation. Concrete generally remains the most cost effective residential frame solution; however, the gap has narrowed and as the CLT supply chain grows, this gap will continue to close. CLT will therefore become a more viable alternative to concrete as long as it is considered early and schemes are designed to match the specific dimensional requirements. A building requiring longer spans or a more complex configuration will likely increase costs above concrete and therefore nullify the advantages of CLT.'  To read the article in full you can visit Building Cost Model: Residential Timber or download the PDF.

 

 

 

Image: Stadthaus, Murray Grove - Will Pryce Photography