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Porch Uplift

Porch Uplift

Porch Uplift

(OP)
I know this is open for interpretation a bit, but would you consider a porch an roof overhang in regards to designing uplift?

Code ASCE = 7-05
roof pitch = 4
V = 100mph
Exposure = C

Also, when figuring GCPi, would you consider the structure to be open on partially enclosed?

RE: Porch Uplift

A porch attached to a building could be looked at as 100% obstructed air flow in one direction and you could probably use the monoslope profile calculations in ASCE7-05 for each component, don't have the table title in front of me but it is one of the tables...
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Roof overhangs have their own calculation and i want to say that the values from this are similar to obstructed open profile mentioned above.
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So I would consider it to act like a roof overhang or as a separate open structure. the loads shouldn't be too much so a little conservative calcualtions shouldn't hurt your design much

RE: Porch Uplift

Yes, you treat it as an overhang. If I'm not mistaken, there's an example in the "Guide To The Wind Load Provisions..." series. Calculate the wind loads for the overall house. For components & cladding, positive wind on the porch roof occurs when it's on the leeward side of the house. Simply use the positive external wind. There is no internal component. Negative wind occurs when the porch is on the windward side, and in this case it's treated as an overhang.

RE: Porch Uplift

I think if they actually acted as overhangs, most would have failed by now based on the super high loads ASCE7 assigns to these. I always treat them as mono-sloped roofs

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