City adopts new tall-buildings wind guidance

The City of London has formally adopted a new set of guidance aimed at limiting the impact of new high-rise development on pedestrians and cyclists at street level.

Claimed by the corporation as the “UK’s first wind microclimate guidelines for new development”, the rules set new standards for the effects of tall buildings on their surroundings and require differing sets of action depending on the height of proposals.

Members of the City’s planning and transportation committee voted to accept the 15-page rulebook, drawn up for the authority by consultants RWDL, at a meeting yesterday. The City said the guidance would take effect immediately.

The move follows concern over the effects of Rafael Viñoly’s Walkie Talkie on street-level wind conditions and, more dramatically, the long-running saga of Aedas’ 112m-tall Bridgewater Place tower in Leeds.

Under the new rules, no action is required for proposals up to 25m in height “unless sensitive pedestrian activities” are intended nearby or the scheme is located near an exposed location, such as the edge of the River Thames.

Computational fluid dynamics (CFD) simulations or wind-tunnel testing are required for proposals of between 25m and 50m in height, or where the proposal is double the height of surrounding buildings. Both kinds of testing are required for buildings up to four times the average height of surrounding structures – or for proposals between 50m and 100m.

For high-rise buildings, defined as being 100m or taller in height, the City guidance calls for either wind-tunnel testing or CFD simulations to support early-stage massing optimisation. For the detailed design stage it demands data from both kinds of study to “demonstrate the performance of the final building design”.

The new guidance also stipulates that where both kinds of assessment are required, they should be conducted by separate consultancies. (See file below)

In a report to yesterday’s meeting, chief planning officer Annie Hampson said that while tunnel tests and CFD modelling were accepted requirements for some categories of new development in the city, the new guidance was aimed at giving developers greater clarity.

“The Wind Microclimate Guidelines are the UK’s first such guidelines and establish a more robust methodology to wind assessments and raises the benchmark for acceptable wind conditions resulting from new development proposals in the City,” she said.

“The guidelines are a result of a consensus from the wind engineering community and are intended to ensure the comfort and safety of pedestrians and cyclists.

“The document is technical guidance to wind engineering practitioners and complements the City’s Transport Strategy and Local Plan which aim to prioritise pedestrians, promote cleaner and healthier ways to travel, and increase the amount of high-quality public space in the City.”

Key elements of the guidelines include the reclassification of previously-acceptable “business walking conditions” as “uncomfortable” and to be avoided; a requirement to assess the variation of mean and gust wind speed and height; and the UK’s first criteria to ensure the safety and comfort of cyclists.