do I need more support here?

[rmclarke]

No, not refering to this forum...the support here is super

Roof supports all glued in today and I've been planning on 1/8" okume ply in and out with ridgid foam insulation.....I don't have any cross supports between the roof members, except for where the vent and the front window will be....so, do I need any? I got to wondering if maybe, given the flat roof style of the hopper, I should put in more support or make the roof 1/4" instead or should I just proceed with my plan ??





Richard

[mikeschn]

Richard,

It honestly looks like plenty of support, especially if it's going to be backed by some EPS insulation. Be sure to glue up the joints real good with titebond III, to prevent the delamination problem I had on the Escape Hatch!



Mike...

[Hoosier Greg]

Although it looks plenty strong now down the road in few years I see what will resemble a roller coaster on your roof. I'm not architect by any means .But I have worked on many roofs with sagging problems. 99% of the time it was caused by the hot sun and too thin of an underpayment (plywood--or OSB board) ..

My suggestion would be rather than cross members ad another spar or two as close to 8" on center..

Now, you might get away without cross members if your roof had a build in arch. From looking at the picture your roof looks fairly flat.. Just my opinion.....


Looking Good ..
Greg.

[48Rob]

Hi Richard,

Using 1/8" ply will work, but it will be a weak roof.
Both from a weight supporting view, and from a structural one.

Your "box" design is fairly strong because of what it is, but the "skin" including the roof, is what really holds everything together.

"IF" the foam is a tight fit between the inner and outer layers of 1/8" ply, and it is all glued together, then you'll have a very strong roof you could walk on.
If all the "parts" are not joined as one, then I'd be concerned were it mine.

Some cross braces are a very good idea, as they go with the thought that joining two pieces as one increases the strength.
I'm not sure what your centers are on the roof supports, but as little as 12" with just 1/8" ply might be too much...
As Greg suggests, 8" on center for 1/8" ply is more realistic.

If I had to promise a customer that the roof would be structurally strong and look reasonably straight, 1/4" ply glued to the roof supports, or two layers of 1/8" glued together and to the roof supports with no more than a 12" on center span would be my choice. (Glued and screwed, mechanical fastening is a must...)

The extra weight, if it is part of an overall concern, is not nearly as heavy as the weight of wondering and worrying for the life of the trailer...or the horrible realization that you must now "take apart" the trailer to "make it stronger"...

Rob

[starleen2]

As A fellow "flat roofer" I can speak from experience that I used 3/8 ply on the roofs of two prevoius designs and both eventually sagged - in the third (current build), I plan to bow the roof line about one inch and add a center brace as well. Nothing is worse than seeing a small lake form on your roof during a rainstorm

[rmclarke]

Thanks everyone for the input

Even though I'm trying to go light here, I don't think 1/4" for the roof will be too much....I definitely do not want 'RRS" (rollercoaster roof syndrome)
And probably a bit more support won't hurt much either.

Richard

[bdosborn]

Its not as much an issue with 1/4" as it is with 1/8" but it might help if you orient the grain of the plywood so it spans the spars as opposed to running parallel to them. 1/8" is definitely stiffer with the grain oriented across the spars.

Bruce

[planovet]

Or, you can just install more spars like James did

http://www.tnttt.com/viewtopic.php?t=24786&highlight=