Lawson Beaufort (UK)
Back to Pedestrian Wind Comfort and Safety
Lawson Beaufort (UK) expresses the Lawson comfort criteria on the Beaufort scale. It has six comfort classes, from sitting to uncomfortable, including separate classes for entrance doors and for roads and car parks. ArchiWind pairs it with Lawson 2001 safety.
Pedestrian Wind Comfort
Comfort checks how often the mean wind speed exceeds the upper limits of Beaufort force 3, 4 and 5.
| Category | Threshold wind speed (mean) | Exceedance probability | Activity | Color |
|---|---|---|---|---|
| A | > B3 (5.6 m/s) | ≤ 1% | Sitting | |
| B | > B3 (5.6 m/s) | ≤ 6% | Standing / entrance doors | |
| C | > B4 (8.25 m/s) | ≤ 4% | Leisure walking | |
| D | > B5 (10.95 m/s) | ≤ 2% | Business walking | |
| E | > B5 (10.95 m/s) | ≤ 6% | Roads and car parks | |
| F | > B5 (10.95 m/s) | > 6% | Uncomfortable |
Exceedance probability is the percentage of time the wind speed exceeds the threshold wind speed, after combining all wind directions. Read the table from the top: each location takes the first category whose condition it meets. Standing and entrance doors share the same limit. Comfort is classified on the mean wind speed; the gust-equivalent mean (GEM) is used for safety only.
Besides the comfort map, the results include the three underlying exceedance maps: the percentage of time the wind exceeds 5.6 m/s (B3), 8.25 m/s (B4) and 10.95 m/s (B5).
Pedestrian Wind Safety
Selecting this scheme uses the Lawson 2001 safety classes below. This pairing is an ArchiWind choice; reports should identify it as Lawson Beaufort comfort / Lawson 2001 safety. Mean wind and gust-equivalent mean (GEM) are assessed separately, using the worse safety class.
| Category | Threshold wind speed (mean / GEM) | Exceedance probability | Meaning | Color |
|---|---|---|---|---|
| A | 15 m/s | ≤ 0.023% | Safe | |
| B | 20 m/s | ≤ 0.023% | Unsafe | |
| C | 20 m/s | > 0.023% | Dangerous |
Exceedance probability is the percentage of time the wind speed exceeds the threshold wind speed, after combining all wind directions. Read the table from the top: each location takes the first class whose condition it meets. Unsafe means winds exceed 15 m/s too often to be Safe, while the time above 20 m/s remains within the limit. Dangerous means winds exceed 20 m/s more often than the limit allows.
For an annual result, 0.023% is approximately two hours per year. The gust calculation is described on the Lawson 2001 page.
Sources
- T. V. Lawson, Building Aerodynamics (2001): the Lawson comfort criteria expressed on the Beaufort scale.