Wind Loads Are Not Simply Horizontal Pressure - They Are Complex, Three-Dimensional Forces That Affect Structure and Envelope
Wind loading on buildings is governed by ASCE 7 (Minimum Design Loads and Associated Criteria for Buildings and Other Structures), which provides procedures for calculating wind pressures on building surfaces. Understanding how wind loads are determined, how they are resisted by the structural system, and how they affect the building envelope (curtain wall, roof uplift, cladding anchorage) is tested on the ARE PPD exam in the integrated building systems and structural design content areas. Architects do not typically perform detailed wind load calculations - that is the structural and facade engineer's work - but they must understand the principles to make informed design decisions about building shape, height, openings, and structural system selection.
Basic Wind Pressure Determination
Per ASCE 7, wind pressure on a building surface is determined by: Basic Wind Speed (V): The 3-second gust wind speed at 33 feet above ground in open terrain for the design risk category, read from ASCE 7 wind speed maps. Wind speed varies by geographic location - coastal areas and high plains have higher design wind speeds than sheltered inland areas. Velocity Pressure (q): Calculated from basic wind speed: q = 0.00256 × K × Kzt × Kd × V² (lbs/sq ft), where K is an exposure coefficient (related to terrain roughness), Kzt is a topographic factor, and Kd is a directionality factor. Pressure Coefficient (Cp): A dimensionless factor that relates the velocity pressure to the actual pressure on specific surfaces of the building (positive on windward walls, negative on leeward and side walls, positive or negative on roof depending on slope and position).
Wind Pressure on Building Surfaces
When wind hits a building, it does not simply push evenly on the windward side. The actual pressure distribution is more complex: the windward wall (facing the wind) experiences positive pressure (pushing in). The leeward wall (facing away from the wind) experiences negative pressure or suction (pulling out). The side walls (parallel to wind direction) experience negative pressure (suction). The roof experiences negative pressure (suction) except on low-slope windward roof sections. Roof corners and edges experience the highest negative pressures - this is why roof edge cladding systems and parapet attachments are some of the most demanding wind-load design elements in a building.
Building Shape and Wind
Building geometry significantly affects wind loading. Taller, narrower buildings have higher wind pressures than low, broad buildings of the same volume. Buildings with irregular plan shapes (set-backs, re-entrant corners) create complex local pressure zones. Rooftop equipment adds to wind loading. Openings in the building envelope (windows, doors, vents) that could allow internal pressurization increase the design wind load on the structural system and envelope.
Key Exam Points
- ASCE 7: standard reference for wind load determination on buildings.
- Basic wind speed (V): from ASCE 7 wind speed maps; varies by location and risk category.
- Velocity pressure q: calculated from wind speed, exposure, topography, directionality.
- Windward: positive pressure (push in). Leeward and side walls: negative (suction). Roof: typically negative (uplift).
- Roof edges and corners: highest local negative pressures; critical design zone for cladding and roofing anchorage.
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