Wind and Shadow Analysis: how a building changes the air and light around it.

It assesses whether wind speeds at the places people actually use (entrances, plazas, walkways, terraces) remain within accepted comfort and safety ranges, judged against a criterion that relates wind speed and frequency to the activity expected there. Sitting outside a cafe tolerates far less wind than walking briskly, so the same wind speed can pass in one location and fail in another.

CFD simulates airflow numerically from a digital model; a wind tunnel tests a physical scale model under controlled flow. CFD is faster, cheaper and easy to iterate during design, which suits massing studies and comfort assessment. Physical wind tunnel testing is still the reference method for structural wind loading on very tall or unusual buildings, and some authorities will specifically ask for it.

Because a building's shadow falls on land the proponent does not own. Planning authorities and building bye-laws in many cities require tall-building proposals to show the shadow cast on neighbouring plots, open spaces and daylight-sensitive uses across the year. Rating systems also address solar access and outdoor comfort, and large developments may face the question during environmental appraisal.

Conventionally the summer and winter solstices and the equinoxes, at set hours through the day, because these bracket the extremes and the mid-range of the sun's annual path. Where a specific authority prescribes dates and hours, those govern. A single-date study is not a shadow analysis, the whole point is the annual range.

During massing, before the footprint and heights are locked. Wind and shadow problems are almost always fixed by geometry (a podium, a setback, a rotated tower, a canopy) and those are cheap decisions early and expensive ones late. A study run after design freeze usually documents a problem instead of preventing it.

They support several, depending on the system: outdoor thermal and wind comfort, natural ventilation strategies, daylight access and site design credits typically require analysis of exactly this kind. The credit language differs between IGBC, GRIHA, LEED and their versions, so the study scope should be set against the specific criteria the project is claiming.

For wind, the usual measures are geometric or mitigative: podium extensions, canopies, screens, porous barriers, landscape and relocating the affected use. For shadow, the remedies are massing changes: reduced height in a critical zone, a shifted footprint or a reoriented tower. Both are practicable while the design is fluid and largely unavailable afterwards.