Shed roof

[TroyC]

Would it be practical to build something like this 20' wide and 40' long? Just thinking.....

[Don P]

Now this is where we might be able to play with another set of beam conditions.

If the rafters are simply spanning 20' then a full cut 2x8 in #2 SYP is probably the bare minimum if there is no snow load. Under just the dead load, self weight, it will probably sag about 5/8" in the center. Under any kind of load and with time I would expect it to get pretty humpty bumpty.

If you meant to say the beams are spaced ~12' apart and the 20' 2x8's are centered over that, well then, the see-saw is just about balanced, but a little bit to the safe side, inboard. Time will be kinder, if the overhang is stiff enough. A 2x8 with a relatively light skip sheath is stiff enough for the overhang in a no snow area, if there is load on it if would need more scrutiny.

Technically the "sweet spot" where everything wants to stay straight and flat is when each overhang is .35 the length of the center span with a uniform load.

[TroyC]

Thanks Don P.

This would be in a no snow load area, central Georgia. All SYP wood. It would be for a sawmill/work area. I'd like to have a 20' between each of the 6 uprights, length and width. Simple 1x4 purlins over the rafters with 29 gauge galvalume. Of course one 40' side elevated a foot or so for some slope.

I probably did not apply the toolbox calculator correctly in figuring the beams or rafters. I was thinking 4 20' beams on 6x6 post with 22' rafters on 16" centers, only 12" or so of overhang.  I'd like to keep as much open span between uprights for loading sawmill and doing tractor work under it. I could not figure if an 8" or 10"  rafter would be appropriate.

I also looked at ridge board gable style roof , but I am trying to keep it simple as possible.

Thanks for any guidance.

[Don P]

Ahh, we're not talking picnic tables and grills.

Full cut 2x8's will work, strength is fine, sag is not great, deeper is stiffer. The beams can be 3 ply 2x12's to make a 6x12. That is stronger than sawing out a 6x12 because it scatters the knots.  If you horizontally board across the knee braces, nailing well to the brace, post and brace, it locks that into a much stiffer bracing unit. You can then lose tapes, pencils, small tools, etc in the Y but they will stay nice and dry.

[TroyC]

Thanks for that info. Makes me think this might actually work!

If 2x12's are cut for the beams instead of a solid beam, is there any benefit to gluing the sandwich? Would nailing or bolting the sandwich be better?

Also, thanks for the bracing tip. Hadn't thought of that.

[Don P]

What the guys with pocket protectors say is that glue in a built up beam adds no strength, but it does add stiffness... and you are mostly in stiffness trouble, so it wouldn't hurt. For this I would nail it. 3 rows down the length, 2" down from the top, 2" up from the bottom, down the centerline. A diagonal pattern, every foot on every line. Hmm, I screwed you up there, at full cut you really should be using 16 commons or even 20's to get penetration depth. It may be worth a box of 6" timberlocks if you don't want to swing that hard that long. ... or 4 plies at 1-1/2" thick and gun nails.

[TroyC]

Thanks again! The plan seems to be coming together!