Pay a premium to reach for the skies, new BCO report finds

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Davis Langdon’s new study explains why the taller you go, the more you pay

Taller buildings are more expensive to build per m2, according to a new study by Davis Langdon. The report argues that as a result, to be viable, the value of tall buildings per m2 must also be higher.

A key finding was that height is not the sole criterion to weigh up when working out the relative value of tall buildings. The other elements affecting cost are the size of the floor plate, the overall proportion of the building, its location and degree of architectural expression.

Davis Langdon looked at the impact of height specifically on the costs of a structure and found that irrespective of floor plate, shape and form, tall buildings cost more to construct per unit of floor area than low-rise buildings.

This is related to:

their increased wind loadings and heavier frames
their vertical transportation needs, such as lifts
the effects of their scale on the movement of materials and manpower.

The report explains that wind loads increase disproportionately with height, bumping up costs of materials and structural members. Meanwhile, the time taken by workers travelling between floors can take up lots of time. These inefficiencies can be addressed, the report said, by rigorous management of the construction process, beginning with detailed planning.

Façades are similarly expensive for tall structures because of the higher wall to floor ratios, with tall slender buildings being the most strongly affected. The report recommends addressing this by rationalising the types of claddings and fixings in order to benefit from bulk buying. Also, it is said to be more efficient and sustainable to use the façade to control heat gain rather than relying on cooling installations.

Davis Langdon further found that plan size could ramp up the cost of tall buildings. It said:

The higher wall-to-floor ratio of a smaller floor plate will result in higher costs
Slender tall buildings need stronger frames to counteract wind action
Higher density lifts will be needed.

Davis Langdon’s findings, written by Steve Watts, have been published in Tall Buildings: A Strategic Design Guide, a book produced by the British Council for Offices and RIBA Publishing.

Key findings:

For a constant floor plate, costs per m2 of floor area increase with height, while overall net to gross floor area efficiencies are reduced.

The cost/height relationship is characterised by step changes, due to technical thresholds that occur at different heights and plate dimensions.

Larger floor plates are more economic, mainly due to their superior net to gross floor area efficiencies and improved wall to floor ratios.

City schemes in high value locations involve a trade-off, with reduced floor area efficiencies and higher cost, due to their more articulated facades, more complex forms and other implications of a more constrained environment.

Groundscrapers can provide more net area for the same overall gross area provision, at much lower construction costs, but involve less intense and potentially less sustainable use of high value land.