Simple Carport Structure?
 

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Folks, this here is your basic shelter of the type popping up outside restaurants and in food cart pods all over the place here. I was thinking about building something like this as a functional-not pretty carport of this construction. However, I’d need it about 4’ wider. Do you think this simple structure would work at that width? How would I calculate the snow load it could take?

Ok, looking at AWC 2021 https://awc.org/codes-and-standards/span-tables/

4” ice ~ 43 psf. I’ve never seen more than 2” accumulate here, at that point trees or their big limbs are coming down, all over my neighborhood. So 4” feels like a reasonable worst case.

Using values for northern Doug fir rafters no 1/2.

At 50 psf live load I can span the required distance using 2x10 on 12” centers or 2x12 on 16” centers. At 40 psf, 2x10 on 16” centers.

I have an idea for the construction of the roof covering to reliably shed snow and ice rather than accumulate it.

My house has asphalt shingles, and retains snow.
I put a metal roof on the carport/woodshed/storage thingy I built, and snow slides off.

Roof pitch is a bit steeper on the house, but it still holds snow.

Do you want to drive in the high side of the roof, and have it slope away, or drive in the side? If you need a large enough opening for a car to drive in, you might want to consider a post frame design, with 3 trusses, or more if you want to hold more vehicles.

As far as snow load and wind load, the truss designing software will size it appropriately.
This is a simple 20 x 20 from the Menards site.

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Where can I find truss design software?

I like the idea as I assume I could use less expensive lumber.

Drive in from side.

I don't think there is such thing as a simple structure. Just how much space do you want to cover? Actually the truss companies use a higher grade lumber. Will likely need proper concrete footings at each post not just for load but so it does not fly away.

You want "#2 and better". No utility grade.

Want to cover 17.5’ x 20.0’, drive in from one of the 17.5’ sides, slope from one 20.0’ side to the other, so rafters need to span 17.5’. Will be on an existing concrete driveway. Need clearance 8’ under lowest rafter.

For a clear span of 17.5, I'd use TJIs instead of dimensional lumber.

My carport spans 24 feet.

I used 24 foot TJIs at 16" o.c. stacked on 2x6 studs, also 16".
It's also the floor for a storage area above. 16 o.c. is probably overkill for just a roof.
24 is more appropriate

http://forums.pelicanparts.com/uploa...1715461389.jpg

...or just go with trusses, and follow the engineering notes

With all the engineered trusses, including steel ones that are actually not too costly, I'd go with something like that. http://forums.pelicanparts.com/uploa...1715559789.jpg
⁸http://forums.pelicanparts.com/uploa...1715560071.jpg

I prefer over built than just enough.
When we did the roof for my shop, the trusses were engineered to hold racks to hang from them.
One day, they will ever be assembled.

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http://forums.pelicanparts.com/uploa...1715560757.jpg
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I went through this exercise designing a 12'W x 20'L patio.

It's a fair bit of engineering to do it yourself, I would look for an off the shelf package that is stamped by an engineer. Or a complete kit that you assemble.

Shouldn't the trusses be sitting on top of the posts?

That has to be a drawing error.

Since I entered the thread, I think I would design with a simple pergola design in mind and then use that structure to attach the poly roof. The benefits are a more pleasing structure, better support of the plastic and a better shade factor. Tinted poly is not as cool as one would think. Between a neighbor and and I, we found that his light green tint as equal to better than my smoke tint.

FWIW, my panels have lasted since 2006. I have replaced some and they stand out as more clear, of course. I might not have had to replace any, but my original attaching process was defective. I didn't predrill larger holes and once a few cracked wind did some damage.

The cover being free standing needs a lot of design consideration. Winds really play havoc with the edges to the point that I tucked them behind facias. I left just enough space for drainage. Any trees around that will drop leaves or sap will be very problematic and should be avoided. Either way, it needs cleaning often.

http://forums.pelicanparts.com/uploa...1715627681.jpg
http://forums.pelicanparts.com/uploa...1715627681.jpg
A couple years ago I built this for an outdoor kitchen at my place in the mountains.
Tinted polycarbonate, screwed together 2x6 rafters, 12" bays. My beams are each 5-2x6 bolted together lams which make a much stronger beam than a 6x8 solid (no worry about splitting grain). I googled the strength of polycarbonate roofing and it's virtually unbreakable (565 PSI). The fasteners would pull out before the plastic would break so it's all about your under pinning. Last winter I had 6 feet of snow on top with no problems

Byron, where do you keep the rest of the bicycles?

Dang that looks perfect. And simple. Love it.

Looking at that above, I see bracing holding it up in one direction what is keeping it from flopping over sideways?

Yes, that is a nice well braced patio that happens to have a cover.
Cover then covering.

Pay no attention the the CAD design. It's not nearly complete and has errors already. That's not even a grape arbor.