18 foot patio beam span material for gabled roof

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Old 09-03-09, 02:07 PM
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18 foot patio beam span material for gabled roof

I am building an 8 foot wide 18 foot long patio cover that I would like to have a gabled roof with 4 posts only. T

I am encountering some very interesting challenges with spanning the 18 foot length with wood or steel or otherwise...

I see there are many companies in Australia (that will not respond to US inquiries) about their clear span technology etc.

Would it be recommended to use I-Beam steel 3x2 4x4 etc or box steel 4x4... or some type of wood or is their lighter aliminum channel type product that would allow for the gable middle and sides? My problem with wood is that for 18 feet the size/weight would be a problem.

The material for the top could even be light steel panels for a typical shed so not a whole lot of load up there unless I go fancy with wood tar and shingles...

Any thoughts / products / etc would be greatly appreciated!
 
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Old 09-03-09, 03:29 PM
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pmullins05,

Welcome to the forums.

Depending on where you are at, what snow and wind loads you may have to meet, etc., in can be done. However, a clear span of 18' will limit how you can go about it. Are you going to pull a bldg. permit for this cover? If so, you'll have to have the plans approved by the bldg. dept., and more than likely they'll have to be engineered.
 
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Old 09-03-09, 05:02 PM
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I may not be able to have a permit due to setback's and fighting city hall... I'm trying to keep the cost down so hiring an engineer is not an option. There is no snow or load that will be on the roof other than the sunshine and the roofing material... possibly metal sheets(light) or plywood/tar paper/shingles(heavier). It seems like in this day and age finding a lightweight metal channel type product used in pre-fabricated storage sheds roofs would be easy to find... but it isn't...
 
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Old 09-03-09, 07:24 PM
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I don't care about the dead weight of the cover, I would be concerned about the loads.

Setbacks are not a reason to avoid a bldg. permit. If it can't be changed so as to come into compliance with the setbacks, get a variance.

What do you have in mind for the footings, and how are you going to attach it to the footings?
 
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Old 09-03-09, 07:50 PM
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I was planning on on using a Simpson ABU44Z Strong Tie adjustable base post with 4 x .5 lag bolts into an 8 inch concrete foundation... The posts would be 4x4 pressure treated wood. The end header board would be 4x6. The frame center post for the top spanning beam would 4x4 wood.
 
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Old 09-03-09, 07:57 PM
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Is this cover going to be attached to the house or free-standing?
 
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Old 09-03-09, 08:48 PM
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The structure will be freestanding.
 
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Old 09-03-09, 08:58 PM
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ABU's won't hold it. They aren't designed for this type of application. They don't offer enough lateral support, don't have enough resistance to rotation of the posts, nor do they provide enough reistance to uplift.
 
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Old 09-03-09, 09:11 PM
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What if I build up a 6 foot cinder block wall on the front and back and tie the ABU into a concrete filled, rebarred 12x12 cinder block? The posts will then only rise about 2 feet from the cinder block. This would also allow for a gate to be put in front and behind the structure..
 
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Old 09-04-09, 04:24 AM
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Rather than go thru all of that, why don't you just 6 holes in the concrete (3 along each side) dig and pour concrete footings and set a CBSQ in the wet concrete of each of the footings.

That would give you a column base that will provide some lateral support, can't twist, and can't be pulled out of the concrete by uplift. That would also reduce your beam span on each of the side beams to less than 9', which you can use a dimensional beam (4X10 or 4X12) to span, and then you could simply truss the roof -- no ridge beam needed..
 
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Old 09-04-09, 05:16 AM
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Just a comment. Have you looked at anything like a web truss design. What comes to mind are the post and beam buildings that use metal plates bolted to the web members. You might be able to get some engineering from a good lumber yard as many design trusses all of the time. Could even work in a curved lower member to improve the looks.

Lefty's concerns about stability are well noted and you can't under estimate the lifting force of a good (bad) wind gust. Speaking from experience as one who watched my 115 pound canoe go sailing across my back yard, 30' up and traveled 200'. A canoe doesn't have a lot of surface area to get a hold of and that was only a 30 to 40 mph gust.

Bud
 
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