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Reinforcing a flat garage roof.

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Oct 10, 2013, 11:56 AM
Reinforcing a flat garage roof.
OK, time to pick some brains.

I've got a flat garage roof, roughly 22x22 feet. It's mostly made of ceiling joists running the same direction but not completely so. It's got two mid support beams, neither reaching across full span. The one is just two 2x6's nailed together and nailed to a semi-central post. It doesn't even have a jack stud so it's only as good as the sheer strength of the nails.

It sags a bit. Water pools on it. Three years ago we had a new torchdown layer put on so at least it's water tight. However, being as I live in Denver, I'm worried that one day my roof will collapse under snow weight.

I'd replace the obviously lousy beam and, as necessary, add whatever I need to strengthen it and, at least, feel better about the snow.

Is there a good way to know just how much beam I need? Tripled 2x10's? 2x8's? Do I need something from the engineered beam list?

I could just go with 2x12's, I supposed, the largest I can get from my local big box lumberyard but they're heavy and I'd rather not use them unless I have to.

FWIW, code for snow load in Denver is 30".

Any thoughts?

Thanks in advance.

A picture is worth a thousand words so here's a quick diagram:


This message has been edited. Last edited by: BigManMark,
Oct 10, 2013, 08:33 PM
First off, the best way to get an accurate answer where you are building enough but not too much will be to have a local to Denver builder or engineer come out to see what you have and need.

From sitting here in Tennessee, I can tell you that there is no way a 22' span roof is going to stay up if it's made of 2x6's. Span loads under normal usage for 2x6 will only be 5' or 6' and that's not counting the massive snow loads you can get.

Don't be surprised to hear that the only way to do this right is a complete rebuild.

Oct 10, 2013, 09:52 PM
any good reason you can't go with a peaked roof if you have to tear it off and redo it? helps the snow run off, especially with dark shingles. with trusses, you can get rid of the post, too.

sig: if this is a new economy, how come they still want my old-fashioned money?
Oct 11, 2013, 10:53 AM
I had a quote of $10k to replace the roof with a low peaked roof built of trusses. He's a family member and a GC so I trust the quote. The job is made harder by the adjoining house which has to have its siding repaired, a door removed, etc.

Yeah, I know the snow loads are a real problem. Code for Denver is 30" and with a flat roof we'd get every bit of that. I've seen 36" in a single day fall.

I was trying to put off the expense to a different year. $10k right now would be hard.