Israeli Criteria (IS 5281)
In Israel, analyses of pedestrian wind comfort and safety conditions are mandated for new — and in certain cases, existing — developments. These criteria, part of the Israel Green Building Standards (IS 5281: Sustainable Building), are used to assess the wind environment in the vicinity of developments.
They address both comfort for various pedestrian activities and safety concerns related to excessive gusts. The guidelines assume open-air conditions and that pedestrians are dressed appropriately for the season (thermal comfort is evaluated separately).
IS 5281 Comfort Categories
| Wind Comfort Category | Exceedance Frequency (Vgust > 6 m/s) | Exceedance Frequency (Vgust > 9 m/s) | Description | Color |
|---|---|---|---|---|
| Seating Zones | ≤ 20% | ≤ 5% | Calm/light breezes, ideal for outdoor restaurants and seating | |
| Entrances | ≤ 25% | ≤ 10% | Gentle breezes suitable for entrances, bus stops, waiting areas | |
| Streets & Parking | ≤ 35% | ≤ 15% | Moderate winds, acceptable for leisurely walking or parking areas | |
| Business / Commercial Areas | > 35% | > 15% | Windy conditions, nuisance for activities, mitigation typically needed |
IS 5281 Safety Criteria
| Wind Safety Rating | Threshold (Vgust) | Exceedance Probability | Description | Color |
|---|---|---|---|---|
| Pass | 20 m/s | < 0.1% | Excessive gusts occur rarely. Suitable for sitting and long stays | |
| Limited Risk | 20 m/s | > 0.1% | “Danger Zone” for sensitive activities; extended stays problematic | |
| Exceeded | 20 m/s | > 0.2% | Unsafe – gusts exceed acceptable limits, affecting balance and footing |
How Wind Speeds Are Calculated in IS 5281
In IS 5281, the wind speed thresholds for comfort and safety are based on a gust-equivalent wind speed (Vgust), not just the mean velocity from CFD. This accounts for turbulence so that two locations with the same mean wind speed but different turbulence intensities may fall into different categories. The formulation is:
$$ V_{\text{gust}} = V_{\text{mean}} + \alpha \cdot \sigma $$
where:
V_mean= average horizontal wind speed from CFD or measurementsσ= standard deviation of wind fluctuations (often estimated from turbulent kinetic energy as $σ \approx \sqrt{2k/3}$)α= gust factor, taken as 3 in IS 5281
This adjustment ensures that gustiness is explicitly captured in all IS 5281 comfort and safety tables.