40x30 Build - roof truss question

[pago cruiser]

Finally moving forward on this.
40W x 30D x 2x6x10' studs. 18 x 8 car door and a 12 x 8 shop roll up door, with a 4' man door on one side. Having questions with the roof.

Design is to match the existing Southwest style home - parapets with cut-outs, stucco, faux vigas beams.

Thinking of sloped top chord trusses, sloped from front to back. This will allow the parapets on front and sides, and then sheet water off the un-parapetted (is that a word?) back. Metal roofing for light weight and durability.

Guess I should have made calls during the week, as our couple local (Tucson) truss shops are closed. I really want the inside garage height level - or I could go with sloping parallel chords. Did a search, but could not find this topic.

From some truss tables, it appears a 16" deep TJI is sufficient for my span, with 40/20 psf live/dead loads. But... I would guess that the sloped top truss has to be minimum 16". How tall at the front? I'm going for minimum slope, maybe 1/4"/ft. But assuming the 16" is the minimum, this would make the truss about 8" taller in the front, to which I would need to then add the appx 12" high parapet. So my 10' high studs + 16" truss min + 8" + 12" parapet = a front height of 13'... (ignoring the 3/4" ply and standing seam metal roofing.) Dang! That's about 12" taller than the house it's adjacent to.

Anything I'm missing? Might have to rethink the inside dimension...

 

[readhead]

TJI is not a truss it is a joist. 1/4"/12" is not a good number for a metal roof. Would recommend rubber.
Are there plans? Is there a building department involved? Are posts a possibility?

 

[pago cruiser]

Thanks for the reply.
I found both 16" deep trusses and TJI's to span 30'.
Could not find any vendors of sloping top TJI's, only trusses. Could not find any dimensions or DATA on spans with sloping top chord trusses. Hence the question. My bad on the description.

From http://www.metalconstruction.org/index.php/applications/low-slope-roofs:
"Low slope structural roofing, generally used on roof pitches ranging from ¼:12 to 3:12, consists of interlocking panels...". I found several companies advertising their products at 1/4"/12". Ergo, I assume this will work? Problem is, if I go more pitch, then my building gets even taller.

I'm about an hour out of town, and even getting Contractors out here to look at the site has been an issue. Rubber roofs around here are pricey. For economics, longevity, and the labor pool in my area, steel seems the best solution.

Yes, there will be full plans to the Pima County Bldg. Dept.

I could use intermediate posts, but I'd rather not. Unless I were to build a wall around them , I think they'd always be in the way...

 

[hippie2cams]

My building is 30x40 and it is set at 3 on 12 and the peak from floor level to peak is approximately 13.8 inches. That doesn't sound to high to me.

 

[pago cruiser]

Thanks for the reply.
The problem is that I can only slope to the back; essentially flat, except for as required for drainage.

My current house has about a 1/12 slope, center peak, gable end. Then the parapets are around the perimeter. But it took a rubber/epdm/plastic whatever to make the drainage work - kinda. I still get ponding as the entire roof (1500 sq,ft.) is then sloped to 4 gutters. I don't want to repeat this with the garage, and the "slope to the back", parapets on front and sides solves that.

But it takes a 16" joist or truss to span 30', and then at minimum slope of 1/4"/ft, another 8 on top of that 16". Add them all up, and the garage is taller than the house by about a foot; assuming I stick with my desired 10' interior height. We are on a hill with a long drive, and it will seem...odd, to approach and see the major structure being the garage. At least it seems to me it will be odd...

Hopefully I can talk to some truss/joist guys tomorrow, and maybe a structural engineer at work. I've seen commercial buildings with nominal 12" steel I beams for near a 30' span, and then purlins perpendicular between the building edges and the I-Beams. Problem is, then I don't know how to get my 1/4" or 1/2" /ft slope.

I can't make the existing house taller, and I can't make the garage lower without site drainage issues; unless I can find a magician truss guy, guess I may have to have 9', or 8' interior...

Dang.

 

[readhead]

Knock the 8" down to 2". Just enough to flash. I install metal roofs. I would not install on that low of a slope. There are way to many pieces to flash and seal. I know the supplier says it will work but if you think rubber is spendy wait until you see what the labor for a properly installed metal roof will be.
You are making yourself crazy here. You need to talk to the engineer and have him design what you need vs what you might do.

 

[ASHMAN_AZ]

Did you finish this build, what local supplier did you end up going through, what type of roof, and how tall were the trusses?

Any finished pictures?