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carports and patio covers

Bender

Bender

SAWHORSE
Joined
Aug 27, 2018
Messages
22
Location
King County
How do you guys deal with stand alone carports and patio covers. I cant see how you can build one perceptively. I have two of these on my desk and i'm scratching my head. i feel like i'm missing something. I'm in Washington state 2015 IRC, seismic zone D, 120mph wind and 30LBS snow. thanks.


Lugarde-Carport-apex-roof-CP4060-p109.jpg
 
Bender, fellow WA guy here, where abouts are you?

And what aspect of prescriptive construction for patio covers/pergolas/carports/etc. has you stumped? Lateral resistance?
 
I believe that the question is regarding bracing. When I was contracting I built a few of these type of structures, utilizing 4" iron columns with a base plate bolted to a reinforced foundation under the slab. This method resisted lateral forces well enough. When you stand a roof structure on 4 to 6 wood posts connected to the slab with simpson AB44 bases it doesn't seen to provide a lot of resistance to collapse. I comprehend how a patio cover resists these forces when attached to a structure. Standing alone is a different situation entirely.
In Bender's photo the posts are at least braced at the post to beam connection. I have seen plenty that haven't even got that detail.
Is there any prescriptive design to refer to when reviewing such a plan? Do these type of structures meet your prescriptive code?
 
I understand your concern now, Is this submitted under and engineer's stamp or by a homeowner/contractor?
Some cities have a standard detail for these types of structures. In CA you might try Davis and the City of LAB&S departments.
An issue as I see it would be the depth & dia. of the footings, given that there is no connection linking them together and no slab.
 
AH101.2 Permitted uses.
Patio covers shall be permitted to be detached from or attached to dwelling units. Patio covers shall be used only for recreational, outdoor living purposes, and not as carports, garages, storage rooms or habitable rooms.
 
Seismic I wouldn't really know, but per IRC, without "walls" wind is not an issue...Very little of what is actually built fits into the prescriptive code, and takes a little digging and alternative means and methods...Like I do not believe there is still a beam chart for decks that addresses anything but a simple span, no cantilevers or multiple spans....But they get approved every day...
 
steveray said:
Seismic I wouldn't really know, but per IRC, without "walls" wind is not an issue...Very little of what is actually built fits into the prescriptive code, and takes a little digging and alternative means and methods...Like I do not believe there is still a beam chart for decks that addresses anything but a simple span, no cantilevers or multiple spans....But they get approved every day...
Click to expand...
Wish this were the case. Locally, wind governs over seismic every time (and we are an SDC D).
 
ADAguy said:
Good illustrations MH,

Steve is obviously not a DP? Why do balloons rise and kites fly?
Click to expand...

They are not buildings, balloons only rise with hot air or filled with something lighter than..o_O.....Try running a building with no true walls through the IRC for wind and let me know how that works out. We were speaking of bracing, not uplift, but we have tables for uplift, so that is a non-issue and can easily be dealt with in the IRC.

Walls are the bigger "sail" which is what is shown in Marks 3rd picture...Without them there are significantly less reactions on a building...

But without Bender chiming back in, we may never know the specifics of his question...
 
Walls or no walls there is uplift when wind passes over a roof due to the upward suction being placed on the roof.

90

Figure 1. Engineers analyze the interactive effects of high winds on a building in terms of four types of building responses: (1) "uplift," the suction of wind on the roof; (2) "shear" or "racking," the tendency of rectangular building elements to deform into out-of-square parallelograms; (3) "sliding," a sideways pushing force; and (4) "overturning," lifting and toppling of the structure from the windward side. An engineered design has to provide for connections of predictable strength to resist all of these assumed load conditions.

Let's take a closer look at just one kind of loading: uplift. When a high wind strikes a house, the flow of air over the roof creates an upward suction, in the same way that wind creates lift on an airplane wing. Wind tries to lift shingles and sheathing off the roof, the roof sheathing pulls up on the roof rafters or trusses, the roof structure pulls up on the wall plates (trying to lift the walls), and the walls pull up on the floor deck or foundation that they rest on. If any connection anywhere along that load path fails, the structure can come apart. It's just one of the ways that wind can destroy a house, but it's an important one and has to be understood, designed for, and built for.
 
Pole buildings are not covered in the IRC, so they can not be build prescriptively. I assume i am not the only one getting "plans" on buildings of these kind, so how have other jurisdictions dealt with these? i believe this would need to be engineered as it falls outside of the prescriptive code. Wind is in fact a big problem for us here and has a long history of damaging/destroying buildings. I hope this clears up what i meant by my original post.
 
If not pre-engineered then it will be up to you to hire an engineer for a pole structure.
Your insurance will not replace it in the event of high wind destruction. If a pre-engineered check their disclaimers.
 
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