Roof Uplift

[drewtheengineer]

With shallow roof pitches, windload on both the leeward and windward sides create an uplift. Logically, this is hard for me to see. How can wind hitting a surface actually lift it up?

I reason it as such... (correct me if I'm wrong)

It's similar to an airplane wing. The air traveling over the top of it has to cover more distance in the same amount of time as the air under it. The air above the wing is "thinner" (perhaps poor terminology), then the air under which creates the lift. Same applies to a roof?

Is this even close?

Drew

 

[boo1]

The vacume or suction on the leeward wall also generates suction. The Normal Force Analysis Method, provides a more accurate description of the wind forces with inward and outward forces acting normal to all exterior surfaces simultaneously.

 

[Taro]

When wind blows past an obstruction, the airflow separates from the obstruction at discontinuities. A vacuum is formed at the discontinuities and suction pressure results.

As the air flows up and over the roof, it doesn't make a sharp turn and follow the roof pitch. The separation between the airflow and the roof surface causes a vacuum (outward design pressure). This also occurs at wall corners as the wind goes around the sides of the building.