Why do penthouses have higher wind loads than the main building?
Penthouses sit above the main roof where wind speeds are highest and there's no shielding from adjacent buildings. Wind speed increases with height following a power law. Additionally, penthouses create localized turbulence and are often in roof corner zones where C&C pressures are highest. A penthouse might see 20-40% higher wind loads than the same structure at ground level.
What structures count as penthouse enclosures?
Penthouse enclosures include: mechanical equipment rooms, elevator machine rooms, stair towers extending above the roof, cooling towers with enclosures, rooftop restaurants or amenity spaces, and any enclosed structure above the main roof level. Each must be designed for wind loads based on its height above ground and exposure.
How much do wind loads increase with height?
Wind speed increases with height following ASCE 7 velocity pressure exposure coefficient (Kz). At 400 feet in Exposure C, Kz is about 1.35 compared to 0.85 at 15 feet. Since pressure is proportional to velocity squared, this means roughly 60% higher pressure at 400 feet. Penthouses on tall buildings need significantly stronger designs.
Do penthouse walls need impact-rated glazing?
In Miami-Dade HVHZ, all glazing in the building envelope must meet impact requirements, including penthouse enclosures. Some engineers argue penthouses above a certain height have reduced debris risk, but current code doesn't provide exceptions. Impact-rated glazing or hurricane shutters are typically required.