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Old 01-24-2012, 11:28 AM   #1
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Roof deck structure question

I'm planning a roof deck (as many converters do) and I'm wondering what size metal tubing is appropriate for spanning an eight-foot-wide roof.

Since the only steel on my former bookmobile is below the floor and in front of the driver, I'd like to use aluminum for the deck crossbeams. I'll be asking the local metal shop what they think is best, but I'd like to go in with a little knowledge. Does anyone have any ideas on what size square tubing I should use for such a structure? Also, what spacing has everyone else used between the lateral beams? Sixteen inches or less? Or greater?

Thanks!
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Old 01-24-2012, 04:25 PM   #2
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Re: Roof deck structure question

How much weight do you intend to put on it?
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Old 01-24-2012, 04:41 PM   #3
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Re: Roof deck structure question

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Originally Posted by chev49
How much weight do you intend to put on it?
I'd like to be able to store a couple of hundred pounds of stuff up there (in two car-top carriers) as well as make it strong enough to support one or two people for lounging in the sun. The carriers will be near the edge on either side of a roof hatch and the people will be aft of that, so it's not like the support beams will need to support everything in one spot.
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Old 01-24-2012, 07:19 PM   #4
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Re: Roof deck structure question

I am supposing that you are going to tie into the existing framework, therefore i would use the same tubing spacing as in the original design. That might also indicate which size tubing to use. I would probably use 2x3 or so, as most of the ribs i have worked with are about this size. But, first, i would see what the skeletal framework was.
As far as weight goes, both the human weight load and the cargo loads are dispersed in a wide range, because all of the structure is welded together, and there are many connections to the original framework. I would certainly gusset all corners if i were doing it, and add center supports as well.
Hope this helps.
Just my two cents worth.
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Old 01-24-2012, 08:51 PM   #5
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Re: Roof deck structure question

Quote:
Originally Posted by chev49
I am supposing that you are going to tie into the existing framework, therefore i would use the same tubing spacing as in the original design. That might also indicate which size tubing to use. I would probably use 2x3 or so, as most of the ribs i have worked with are about this size. But, first, i would see what the skeletal framework was.
As far as weight goes, both the human weight load and the cargo loads are dispersed in a wide range, because all of the structure is welded together, and there are many connections to the original framework. I would certainly gusset all corners if i were doing it, and add center supports as well.
Hope this helps.
Just my two cents worth.
Your suggestions gave me an idea: I'm thinking I can use 2x6 pressure-treated boards to span the width and rest the edge of the boards on the roof itself. The roof is arched (to about two inches above the edge rails), so I can create a template of the arch and cut the bottom of the wood planks to exactly fit the curve of the roofline and place these boards directly over the existing roof support beams inside the ceiling. At the sides of the roof I can tie the boards into the structure with foot-long square tubing bolted through the wall skin below the roof. This will keep the boards from flopping over until the deck planks are attached and once that's done, the whole system should be very sturdy. In addition, the solid structure below the deck should be slightly more aerodynamic than a raised platform as it would force all air flow over the top instead of through a maze of complicated tubing. I think a single layer of double-stick foam tape would sufficiently protect the roof surface from chafing on the wood beams.

Something like this:


What do you think?
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Old 01-24-2012, 09:23 PM   #6
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Re: Roof deck structure question

That would probably work. I would make sure that you had long enough side braces and that they went into the ribs and not just the sheet metal skin. I also imagine that making the cross ribs of wood, could take quite a while, but 2x6 pressure treated would stand the weather.. and for decking you could use the plastic board decking material, which works great, and is very tough.
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Old 01-24-2012, 09:54 PM   #7
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Re: Roof deck structure question

Quote:
Originally Posted by chev49
That would probably work. I would make sure that you had long enough side braces and that they went into the ribs and not just the sheet metal skin. I also imagine that making the cross ribs of wood, could take quite a while, but 2x6 pressure treated would stand the weather.. and for decking you could use the plastic board decking material, which works great, and is very tough.
My thoughts exactly.

The wall skin is 1/8" aluminum. The bracing wouldn't support any weight (the weight of the deck is carried by the roof itself) so I would think that simple carriage bolts through the braces with washers and locknuts inside the wall would be enough to prevent the brace from rotating during acceleration or braking.

I also think the labor saved by simply screwing the decking to the cross beams (as opposed to through-bolting into metal tubing) would offset the increased time spent cutting the beams to fit the contour of the roof.
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Old 01-25-2012, 12:30 AM   #8
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Re: Roof deck structure question

I think all that would work, but the bolts are for supporting weight, and the main problem of course is vibration after bouncing all the time, and not necessarily acceleration of the bus or normal braking. for any bolts, besides washers, etc, nyloc or other locking nuts is a good idea.

Hope this helps.
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Old 01-25-2012, 07:17 AM   #9
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Re: Roof deck structure question

I like the idea of wooden "joists" that match the curve of the roof.
I did that once on a friend's bus. I used silicone and L brackets to hold them on to the metal roof surface. Then at the ends of the boards I attached a "rim joist" that ran from the front of the deck to the rear of the deck. I attached the "rim joist" to the ends of the floor joists with screws. I also siliconed the inside of the "rim joist" to the metal roof surface.

It was very sturdy.

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Old 01-25-2012, 08:01 AM   #10
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Re: Roof deck structure question

Quote:
Originally Posted by Accordion
I like the idea of wooden "joists" that match the curve of the roof.
I did that once on a friend's bus. I used silicone and L brackets to hold them on to the metal roof surface. Then at the ends of the boards I attached a "rim joist" that ran from the front of the deck to the rear of the deck. I attached the "rim joist" to the ends of the floor joists with screws. I also siliconed the inside of the "rim joist" to the metal roof surface.

It was very sturdy.

Yeah! I like that! Thanks.
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