What size beam for canopy over my deck?


Old 06-22-14, 10:59 PM
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What size beam for canopy over my deck?

There is currently a canopy over my deck which looks like it was brought in from somewhere else because it is of older materials and is just sitting on the deck (the posts do not go all the way through to the ground). It basically has 2 4x6x24' beams running parallel 12 feet apart being supported by 3 4x4 posts on each beam. There are 16' 2x6's on top of that (they overhang 2' on each beam) with corrugated fiberglass panels. I want to rebuild it because it leaks and I want the posts to go all the way to the ground so they aren't sitting on the deck and am probably going to use fiberglass panels again. This canopy is against the house so I may also want to attach one end to the house so I can eliminate one of the beams. My question is, instead of using a 4x6 with a post in the middle like there is now, could I run a larger beam and eliminate the post in the middle? There won't be much weight up there with just the fiberglass and I live in Seattle so it rarely snows but this will need to have a pretty low pitch to the roof. The other option I thought about was putting a solid roof with either roll roofing or shingles to match the house if I can make it steep enough, but I would imagine that would be too heavy to do without the middle post if I go that route, right? The overall size of this canopy is going to be 24' long and somewhere between 12-16' wide.
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Old 06-23-14, 05:42 PM
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Some pics would help. The structure that you described doesn't sound like it meets code. Attaching it to the house doesn't sound like a good idea. There are some really nice all year round awnings available that do everything that the canopy does.
Old 06-24-14, 12:49 AM
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For a beam to span a 24', using conservative design (40 PSF) load values, with joists at 24" centers, you'd need a steel beam with a Section Modulus of about 21.6 C.I. Something like a W 12 x 19, meaning the beam will weigh about 500 lb., or close to a quarter ton. Are you prepared to lift something like that into place? Serious thought should be given to leaving the center columns in place.

And forget about shingles. They are not designed for low-slope roofs, and will leak. You already have the leaks, right, so why not go with something that won't leak?
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