how to calculate corner post size for patio cover?

stash-hdyNovember 19, 2009

How can the size of a corner post be calculated? Building a patio cover that will be attached to the house on one side and off the roof for its width. If I calculate the weight of the materials can I estimate the weight on the corner post by dividing the weight by say 3 or 4. The front beam will be supported by the house at one end by the house and the post on the other, The front beam will be a double 2x12 16 feet long. The cover will extend approximately 10 feet from the house. So the cover is 10 x16 supported by the house for 10 feet, along the roof for 16 feet and open on the front for 16 feet and one side for 10 feet. Rafters and ceilng joists for structure attached to the house. Any suggestions would be appreciated.

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brickeyee

"If I calculate the weight of the materials can I estimate the weight on the corner post by dividing the weight by say 3 or 4."

You calculate the area the post is supporting, including any required snow loads, and wind uplift loads.

The weight bearing capacity of wood is actually very high, but you must check for both pounds per square inch loading and buckling of the post.

You also never cut the load tight since that makes the slightest error have a large effect.

Wood defects (grain run out, knots), errors in perpendicular, etc.

Required margins to account for materials and actual construction are rather large.

    Bookmark   November 19, 2009 at 9:15AM
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stash-hdy

The materials will weigh approximately 2800 pounds, the corner post I want to use is rated for 3000lbs. It should be fine , thanks for the input

    Bookmark   November 19, 2009 at 9:33PM
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manhattan42

You need a to hire a local structural engineer or architect to do your calculations.

No answer from any other source will suffice.

    Bookmark   November 19, 2009 at 11:59PM
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brickeyee

"The materials will weigh approximately 2800 pounds, the corner post I want to use is rated for 3000lbs. It should be fine , thanks for the input"

That would be cutting it very close.

Add a couple workers up there during constriction and you could cause cracks.

No snow loads?

Get a local PE to size things and stamp off the plans.
The AHJ is unlikely to accept anything less since you are not building 'per se' according to eh code.

    Bookmark   November 20, 2009 at 8:31AM
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macv

I suspect the OP is talking about the dead weight of the entire roof so, if I understand the odd description, the post should only need to support a quarter of that. If there is a snow load, I would be more concerned about the beam.

The OP should definitely consult a professional who can actually look at the conditions. The description here is too unclear to use as the basis for design advice.

    Bookmark   November 20, 2009 at 9:09AM
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stash-hdy

There is no snow load and the weight is dead weight. I will consult a structural engineer if I can find one.

    Bookmark   November 20, 2009 at 10:53AM
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sierraeast

Even death valley has a snow load,(20 p.s.f.) and here in the mojave desert, we are at 40. Every once in a while ma nature rears her ugly head and we get dumped on with roofs collapsing because of the "only 40" snow load requirements. In fairness, it's typically older homes pre-codes that get damaged. That's why it's always a safe bet to go over kill in certain structural applications. Definetely seek out a reputable, licensed engineer.

    Bookmark   November 20, 2009 at 12:15PM
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macv

The Gulf coast, a third of Georgia, and the entire state of Florida has a zero ground snow load according to the 2003 IRC. Of course, they have even more serious weather problems.

    Bookmark   November 20, 2009 at 2:15PM
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