Wind

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mojdehazani

September 17, 2025 00:26

I’m studying for PDD/PPD and came across a practice problem asking: “Which roof type experiences the most wind uplift, and which experiences the least?” The options were: 1. Flat roof 2. Curved/barrel roof 3. Shed roof (single slope) 4. Gable roof – high pitch 5. Gable roof – low pitch From my understanding, curved/barrel roofs often experience the greatest uplift because wind accelerates as it flows over the curve, but I’d love to hear how others have reasoned through this type of question.

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  Ralph Hale September 18, 2025 16:16

  Great question - anytime aerodynamics is involved, the real answer is "it depends" - an answer for one building shape might not be the same for another building shape with the wind coming from the same direction.  Change the wind direction and you get a different answer sometimes. In general, more obstruction of the wind creates more wind forces.
  
  Uplift is usually worst with large gable ends and large overhangs - they are significant obstructions of wind flow.  Hipped roofs and domed roofs are best because they don't have any real place for the wind to "catch", and generally, steep gable roofs with large overhangs are particularly bad, because the high end wall concentrates uplift forces and the overhang catches the concentrated wind.  Flat roofs and low-pitch gable roofs generally perform better because they are lower-profile - they present less roof to obstruct the wind. 
  
  In looking, I don't see any research about barrel-vaulted roofs and wind uplift to compare with, but Mansard and gambrel (barn-style) roofs are generally considered above-average choices for high-wind areas, and have similar (but admittedly not the same) profiles to a barrel-vault - their shape presents less obstruction to the wind than a steep gable roof covering the same area and shape of structure.  
  
  https://basc.pnnl.gov/resource-guides/hip-roof-vs-gable-roof#edit-group-scope
  
  It's fairly easy, but does take a good bit of computer time, to run simple CFD simulations in Rhino using the Butterfly plugin for Grasshopper - model a series of buildings, run the simulation with 3 different wind angles, and see which building shows the highest uplift forces. 
  
  Best,
  Ralph, the Amber Book Team

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