porch roof cantilever diaphragm connection?
porch roof cantilever diaphragm connection?
(OP)
I have a covered porch open on three sides on the coast (high wind area) but no seismic. The open two corners are supported by brick columns. I am tasked with designing a new roof at a higher height (2-3ft) than the exising roof. I plan to design the porch roof as a cantilever diaphragm to resist lateral wind loads. I will be extending the ex. brick columns w/ wood posts and using them for gravity loads only. the side adjacent to the ex. roof will likely sit on a cripple wall and/or lvl. I plan to detail 45°bracing down to the existing roof height to transfer the diaphragm forces into the existing diaphragm on the one side of the porch only. Does anyone if this approach is permissible by IBC/IRC? and or know of any special considerations I should look it? thanks






RE: porch roof cantilever diaphragm connection?
BA
RE: porch roof cantilever diaphragm connection?
DaveAtkins
RE: porch roof cantilever diaphragm connection?
Mike McCann
MMC Engineering
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RE: porch roof cantilever diaphragm connection?
I'd say they all fail in uplift before they have a chance to fail because of diaphragm issues. I see porches all the time built on 4" unreinforced SOG, and then sometimes THOSE get converted to liveable spaces.
Not saying that its right, just saying that is what I suspect... After the 2004 hurricanes in Florida every contractor and his brother was out there replacing aluminum porch roofs and pool screen enclosures.
jgeng- if the porch has no walls, then there may be very little to negligible lateral force, except from your brick columns. But I suppose you have considered that.
RE: porch roof cantilever diaphragm connection?
RE: porch roof cantilever diaphragm connection?
RE: porch roof cantilever diaphragm connection?
If you field verify the post has no uplift connections, this may constitute a "dangerous condition" or some other trigger mechanism that gives you solid code backing to show the client you must correct the situation. You can also tell the client (hopefully talk to the homeowner), if you determine it so, "Look, to the letter of the code, we do not have to do this. But why spend all this money on this new porch and have something that can blow away the next hurricane/storm when we can fix it now." Brick work can be pricey but its not gold, you are already adding a new roof..
For your project, are they removing the existing roof and then reframing it? If this is the case, some codes may require you to then bring the rest of the supporting vertical structure up to current code (ie columns, footings, connections).
Sometimes this is also based on square footage or $$ of the project, though I would not think you are triggering either of these for a porch renovation.