Roof structure material selection help request

[MatBirch]

I’m building a sort of canned ham/ bread loaf trailer, 13’ long x 8’ wide. My original intent was to go as a foamy, but in my world, that actually wound up to be far more expensive. I’ve changed things up and going with a very simple frame and skin plan. My hangup at this point is the roof. I need to select material to build the trusses out of. It won’t be a walk on, and snow load is fairly light here. I just want to make sure that it doesn’t sag over time. I’m figuring I’ll put a 1” crown on the roof to help with this.
So...
I’ll be cutting the crown shape into each truss, but what material to use?
I believe I can stay in the. range of 1-1/2” thick at the tapered end at the walls. This will leave me with decent headroom, and keep the overall height where I need to facilitate storing the trailer.
2x ?? I can use 2x3, and not have too much waste. Heavy, and the quality of the wood they use to produce dimensional lumber (especially 2x3, 2x2, 1x2) is less than stellar these days.
3/4” plywood ?? 2 layers laminated, glued and stapled.
Since I’d be laminating it, I can get the material free, utilizing offcuts from work. This is how I built my wall profiles, which turned out very strong.
Any other thoughts? Multiple layers of thinner plywood?

The entire interior will sprayed with about 1-1/4” of 2# expanding urethane foam. This stuff bonds incredibly, and while not providing any structure per se, it does serve to tie everything together, and make it far stiffer, and more solid.

[OP827]

Plywood is not a good material for roof trusses simply because half of the grain is in the wrong direction to tension stress. Laminated strips are going to be stronger than general lumber wood due to less defects and glue being stronger than wood.

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[les45]

I used common pine 1X2's (actually 1X4's split) doubled on 12" centers for my 12X7 retro standy. I insulated with 1.5" foam board and skinned the top with 5mm Revolution ply which I also used for the interior ceiling. I stapled all the plywood every 4". Rather than crown the spars transversely, I simply sloped the roof line in both directions from center primarily for looks and drainage. I pulled a 10 lb weight on the center of the doubled 1X2's and only got 1/8" deflection and that was before the insulation and skins. I wouldn't stand on it but I'm not seeing any sag. I plan to seal the roof with an EPDM membrane.

You can see details with pics in my journal at : http://tnttt.com/viewtopic.php?f=50&t=70991

[MatBirch]

Well, I hmm’d and hww’d over this for too long already, so I went on a shopping trip yesterday.
I settled on some 2x3 Doug fir. It took some digging, but I found enough stock with some good grain in the correct orientation


I marked the taper I wanted on them, and cut them with a skilsaw.



I then stacked them all together, clamped them up, and kissed them with a belt sander to ease the transition, and make them nice and uniform , and ready to play nice together.


Quite pleased with the end result!