Scissor trusses or not?

[Cuda416]

Good morning everyone, hopefully you've all had your coffee and are ready to today's question from me regarding my upcoming pole barn/shop build.

Turns out adding scissor trusses for my building is a whopping $261 over the base price and so at first this seemed like a no-brainer. Then I started reading about ceilings for them and it appears the load rating for the bottom chord for these things is almost always zero because they are designed to withstand top loads only and can actually pull apart if a ceiling is applied to them which then cause the roof to collapse.

Whoah!, say what!??

Is it just me (possible) or do they present a serious safety issue for pole barns?

it is better to just use the "standard" flat bottom trusses if I don't need the extra height?

 

[Thumper68]

If that were true than there would be millions of homes with failed ceilings.

The truss manufacturer can give you the proper specs for what the truss can support.

I like a vaulted ceiling in the shop, give much more room when working with longer items.

So for me it would depend on side wall height, I have 14 foot side walls and a vaulted ceiling.

 

[ssdave]

No need to guess. Ask the truss manufacturer that is quoting your trusses. The bottom chord load rating will be printed on the truss diagrams, usually it is 10 psf, which is quite adequate for drywall as well as lights, door mounts, etc.

 

[d300]

Trusses are designed for the intended/anticipated loads. If you want to hang a bunch of weight then tell the designer and that is what you will get. As the span increases or the weight increases then the truss members will get bigger. Simply no mystery.
FWIW, I just installed some 42' scissors on my new house and they have an increased bottom chord load design.

.

 

[Cuda416]

Thanks Thumper68, Although that was one of my initial thoughts, I was a bit alarmed by how many posts I saw concerning this and I am still waiting for the numbers come back. My concern is a little more amplified by a 36' span across my proposed building. I'll have a 14' wall height as well and yes, the extra height will be nice to have.

 

[Cuda416]

No need to guess. Ask the truss manufacturer that is quoting your trusses. The bottom chord load rating will be printed on the truss diagrams, usually it is 10 psf, which is quite adequate for drywall as well as lights, door mounts, etc.

Yep, i am waiting on the numbers to come back. Sounds like from what has been said so far, it's sort of an urban myth at this point.

 

[Cuda416]

Trusses are designed for the intended/anticipated loads. If you want to hang a bunch of weight then tell the designer and that is what you will get. As the span increases or the weight increases then the truss members will get bigger. Simply no mystery.
FWIW, I just installed some 42' scissors on my new house and they have an increased bottom chord load design.

.

Thanks, safe to assume you don't have open trusses in your home and have put a ceiling under them too. Good stuff.

 

[Cuda416]

No need to guess. Ask the truss manufacturer that is quoting your trusses. The bottom chord load rating will be printed on the truss diagrams, usually it is 10 psf, which is quite adequate for drywall as well as lights, door mounts, etc.

You were spot on, they got back to me and said they would adjust the design to support a ceiling load. A little more cost, but that should be expect I suppose.

Thanks again

 

[Cuda416]

Actually, it's more correct to say you were all spot on. Thanks everyone for such quick responses. I'll be pulling the trigger this week on my kit. Getting pretty excited to get started.

 

[6768rogues]

Have the truss designer design them for your use. For a ceiling and insulation, have them put 10 psi dead load on the bottom chord. No big deal, they can design whatever you want.
I have a 14" high ceiling in two of my buildings. It is plenty high for a lift. I did not need the extra height and it would have been more air to heat and cool.

 

[yeldogt]

I'm confused .. what are you worried about ?

I like using them -- you get a very steep roof line outside and a nicer ceiling line inside.

 

[Cuda416]

I'm confused .. what are you worried about ?

I like using them -- you get a very steep roof line outside and a nicer ceiling line inside.

I was reading all sorts of things saying you can't hang anything, including sheetrock or anything of any weight from them or they can collapse. it was a knee jerk reaction to reading a few posts. My designer is going to make the change for me. I admit I was a bit confused.

 

[BIG-BRO]

Here's my new garage with 38' span scissor trusses. Bottom chord is rated for 10 psf and will carry insulation, sheetrock and lights. Outer pitch is 7/12 and inside is 4/12. Plenty to carry snow load here in New Hampshire.

 

[rburke65]

Oooh....you're going to like the new garage! Good for you!

 

[Cuda416]

Here's my new garage with 38' span scissor trusses. Bottom chord is rated for 10 psf and will carry insulation, sheetrock and lights. Outer pitch is 7/12 and inside is 4/12. Plenty to carry snow load here in New Hampshire.

Thanks for the picture. I expect to hear from my designer today. I'm itching to get started....

 

[yeldogt]

I was reading all sorts of things saying you can't hang anything, including sheetrock or anything of any weight from them or they can collapse. it was a knee jerk reaction to reading a few posts. My designer is going to make the change for me. I admit I was a bit confused.

It's a question of material size ... basically, a scissor is a roof within a roof ... look at the picture.

They are extremely strong -- especially when held together with plywood. -- the force wants to push the walls out.

 

[Cuda416]

It's a question of material size ... basically, a scissor is a roof within a roof ... look at the picture.

They are extremely strong -- especially when held together with plywood. -- the force wants to push the walls out.

I understand the basic structure, just wasn't sure about the loading of the lower chord. I agree since they will want to push the walls out, they "should" be pretty darn strong no matter what, but that assumes the walls are hard to push out

I think it's safe to say that's not going to be "easy:. I was just very surprised to read anything related to them collapsing at all because of the very reason you state.

Thanks

 

[Cuda416]

Scissor trusses have been ordered (for a surprisingly small difference) at 10psf. Thanks for the info everyone!

 

[Blk88GT]

No issues with mine, 40' span in the great white north....