Porch Addition Uplift 1

[Juanchoganda]

I have a project in Miami, FL where the client wants to add a roofed porch attached at the back of a residence? I'm thinking of adding 2x rafters with a wood beam and post to support it.

What kind of pressures should be used to to check the uplift on the structure? Should it be the roof or overhang pressure from the residence C&C values? or should I do a separate wind analysis using open structure values?

 

[driftLimiter]

C&C pressures for an overhang should yield a pretty high value. There is no harm in checking what the uplift pressure would be if you analyze it via open structure. Best to take the max of the two and design. Also concerning to me is the positive anchorage of the deck to the existing structure. Don't skimp out on this load path. Simpson has some nifty connectors for that (DTT1Z, DTT2Z) there are other ways to accomplish it.

 

[JStructsteel]

How about open structure pressure with obstruction (the walls) and see how that compares?

 

[Juanchoganda]

I was using the C&C values to check on the beam and footing uplift and I was getting large members to work but it seems that I was heading the right direction.

Thanks for the suggestions, I'll try those methods and compare.

 

[RPGs]

I agree you're going to get some very large net uplift using C&C values. Particularly if you're using a accurate dead loads for your wood framing--the stuff is really quite light.

It's good to be safe of course, but the contractor might be totally confused by the sheer amount of fasteners you specify to resolve the net uplift. I really recommend taking the time to do the open building analysis.