I’d like to build a carport. It will basically just be a shed roof extending off the front of my garage. I’ll need a beam, as thin as possible, to span 22 feet from side to side.
It looks to me like steel is the only thing that could easily do that, but the cost is high, and how thick does it have to be? I priced out some 6" i-beams. $500 each. How do I attach wood to those? Can’t exactly nail into them.
That brings me to LVLs and such. Less pricey, but very thick. I suppose I could double up on a couple of thinner ones (like 6") but they don’t seem to be rated for exterior use, and I’m pretty sure a carport would be considered exterior use, even though they’d be under a roof.
Any guidance?
The advantage of LVLs are that
- you can put them up 1 ply at a time
- they hold nails/cut easily
- the lumber yard will likely size them for you if you ask
The disadvantage is that the depth will be about 1/16th of the span when using 2-3 plies.
The advantage of steel is that an I beam (W shape is what you want, for “Wide Flange Beam”) will be about 2/3 the depth of an LVL. The disadvantages are
- An engineer will likely charge you about $600-800 to size this beam, but will also tell you how to top connect it
- It will be one piece (fwiw it will weigh about the same as the LVL)
- You will have to buy a 40’ piece, or pay a premium to have it cut down from a 40’ piece. (stock lengths of steel are 20’/40’)
Note that nobody can properly answer your question from the data given (edit - just notice you mentioned 16’ rafters below). You would need to include the span of the rafters and (at least) your location to determine the snow loads and wind loads (edit: and seismic, though it’s unlikely to control for this design) for sizing the connections.
Disclaimer: I’m a structural engineer, but I’m not your structural engineer. For a long span like this I recommend contacting someone licensed in your jurisdiction to help you out.
Not their structural engineer yet!
They’re our structural engineer now, Dave.
One option would be to make the beam a flush condition. To get a 16’ span with rafters you’re going to be using at least 2x8s. That’s 7.25" deep. If you were set the top of the beam at the top of the rafters and hang them from the beam (simpson or USP hangers) that buys you some space. Now an 11.88" LVL would only stick down 5-5/8" below the bottom of the rafters. (okay, 5-3/4"-6" with the additional slope over the 5.25" of beam) I’m not saying that a 3 ply 11x88 LVL with a 2.1E, bearing in a BC6 cap on 6x6s would work for your application, but the height tolerance would seem to add up in your favor.
22 ft unsupported seems like a very long span to me, what’s that nearly 7 metres?
Sounds like it’s getting into the realm of structural enginneering not diy for me.If you want to save costs you might think aout a “flitch beam”, that’s 2 wood beams with a steel plate sandwiched in between - the three components are bolted together every few feet. Easier to join to the timbers then.
https://www.youtube.com/watch?v=QWUNd559UQYI still think you might be more like 10"x2 or even 12"x2 timbers to cover that span if totally unsupported. But might still come in a little cheaper than the i-beam.
Maybe the roof will be very lightweight and no snow weight is expected - but I’m no structural engineer so don’t take my word for it.Other features like corner bracing or canti-leverage, or some other support structure or other feature (like is it the bottom side of a framed gable triangle) might also help.
LVLmight not be suitable, but i think you can get treated “glulam” beams suitable for exterior (covered) use.
https://en.k2-builders.com/what-type-of-glulam-can-be-used-for-exterior/A flitch beam sounds interesting. The problem with 2-by timbers, like 10x2 or 12x2, is their thickness. A 12x2 would drop down 12 inches, and the highest point of my carport is only 8-feet high. In its 16-foot run, it has to drop at least 4 inches in order for water to run off. I can’t be using material as thick as 12x2. That’s why I was considering doubling or tripling some engineered wood. But at that point it seems like steel would be the same cost and better performing. I dunno. Like you said, I may have to talk to an engineer.
yeah, glulam is probably a non-starter too if there’s no height available.
I think you can do triple flitch.So like : [w]|[w]|[w]
maybe that’d work with 3 2x6s , 2 steels, all boted together.
To attach wood to an I-beam, you could drill holes in the flanges of the beam, then use bolts. There are also fittings that you can slide posts & beams into, with various ways of securing them to the material they hold. If you’re not using T-shaped fittings, you could bolt fittings together.
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Try an image search for “beam connectors” and you should get an idea of the types of things that are available, but a trip to your local builders’ merchant & a chat with the people there may be more fruitful.
Easiest thing to do is talk to a metal building company. They do carports all the time. Even if you don’t have them do it, you could get detailed info on materials.
Any reason the high side of the shed roof can’t intercept the existing garage roof further up the pitch? Then you could use open web trusses which although deeper are lighter and potentially cheaper than a wide flange. Attaching them higher also gives you more clear height with a longer span.
That was the original plan. I was going to just extend the existing roof outward, but it would shed rain directly where you have to walk to get to the cars. You’d basically have to walk through a waterfall.
It would shed rain off the low end? Can you use a gutter and downspout?