Scisssor Truss or Ridge Beam?

[Green]

Ok, first post be gentle...

Looking to build a 40' x 60' x 12' structure. It will be residential. Building on a slab, mostly. Slab will be 40' x 35' with the remaining 25' being a "basement". That portion of the overall size will be 3' below grade.

12' walls will allow a second story in the 40' x 25' section, while from the outside you would simply see a 40' x 60' x 12' structure.

Here's my dilema: I need/want vaulted ceilings in order to make the second floor idea work (more accurately a split level on the inside). The Slab portion of the home needs to be a 40' clear span. I don't want any interior walls in that portion of the home.

I've explored the possibility of using something like Miracle Truss (or many other similar companies). That option is viable from the standpoint of being able to span that great of a distance, but seems costly. I plan on building the walls out of 2x8.

1) Can I get engineered scissor trusses with a 40' clear span? (I've emailed a few truss companies, but no responses so far)

2) Is a Ridge Beam and rafters an option? That seems like an extremely long span for an unsupported ridge beam.

3) Should I just consider a lite-gauge steel frame/red iron frame combination instead?

Any thoughts (besides I'm crazy?)

[Don_P]

You're crazy :)
I'd look into trusses. You're pretty much out of the ridge beam and stick frame size. At over 32 wide this is an engineer req'd building.

[bighammer]

the above project sounds fun, but will also keep you busy. I would be sure to check with your engineer about pitch on your trusses. I bet your going to have raise your sidewall height to acheive 2nd story living. I have framed some post-to-truss buildings and they typ. have a 4/12 pitch. With the min. amount of deflection they could have a 1 1/2 / 4 pitch on the inside.....or something like that...keep us informed...how far apart are your trusses going to span??

[Richard A Hetzel]

I just did a house with clear-span scissor trusses spanning 38 feet. The pitches were 6/12 on the top chord and 3/12 on the bottom chord. You need a fairly big difference in pitches in order for the trusses to have enough depth. The house was about 86 feet long, and had a few different kinds of trusses, and the cost of the trusses was about $16,000 in northeast Pennsylvania.

[Green]

You are both correct... Initially I was looking at using an engineered steel scissor truss. The inside pitch would have more closely matched the outside pitch allowing me to ignore the "rule of 3" that would apply to lumber built scissor trusses.

I will either have to stick with my original thoughts or raise the pitch in order to achieve the correct amount of headroom for the upper level. The 12' walls will still give me an approximate 6' sidewall height. I guess another option would be to raise my sidewall height in for that portion to 14' and go with a common truss/flat ceiling. That would also help break up the roofline.