The City of London’s guidelines for wind microclimate ensure that wind conditions around public spaces are safe and comfortable, enhancing the overall usability of outdoor areas. The City of London uses a modified version of Lawson Wind Criteria named City Lawson Criteria. The categories and respective colors are shown below.
| Comfort Category | Mean and GEM wind speed (5% exceedance) | Description | Colour |
|---|---|---|---|
| Frequent Sitting | 2.5 m/s | Acceptable for frequent outdoor sitting use, e.g. restaurant, café. | Grey |
| Occasional Sitting | 4 m/s | Acceptable for occasional outdoor seating, e.g. general public outdoor spaces, balconies and terraces intended for occasional use, etc. | Blue |
| Standing | 6 m/s | Acceptable for entrances, bus stops, covered walkways or passageways beneath buildings. | Green |
| Walking | 8 m/s | Acceptable for external pavements, walkways. | Yellow |
| Uncomfortable and/or Unsafe | > 8 m/s | Not comfortable for regular pedestrian access. | Red |
Key changes from the Lawson Wind Criteria include:
- The Frequent Sitting category was altered to reflect the City of London’s goal to create more active public spaces with café and restaurant seating areas.
- The Uncomfortable category was renamed due to feedback that the Lawson Business Walking conditions often lead to complaints. This category is now only applicable to areas not expected to have regular public foot traffic.
It is important to differentiate between the definition of the calculations behind the City of London wind comfort metric and the definition of the simulation process defined by the City of London regulatory guidelines. While Orbital Stack implements the calculation of the City of London wind and thermal comfort criteria, Orbital Stack offers many different levels of simulation, some of which may not meet the regulatory requirements of the City of London. For example, many studies will need both CFD and wind tunnel testing for City of London submission, CFD evaluations require very specific simulation settings, and AI simulations are not currently an accepted approach. Please refer to the official City of London documentation for a comprehensive review of all requirements.
City of London Color Legend
What is it measuring?
The color scale indicates pedestrian wind comfort according to City Lawson Criteria. Results are divided into comfort categories ranging from Frequent Sitting to Uncomfortable.
What options can I specify?
The Season and Time of Day ranges.
*Note: The City of London criteria are also used in Birmingham and Leeds but are not referred to by that name in those locations.
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