why use roof trusses?

[Mosey]

I'm still pondering how to go about building a pole barn with a higher than normal ceiling, 14 feet. I was thinking I would just build the walls 14 feet high, then use roof trusses. But, now I'm thinking that maybe it would be better to not use trusses and just use a center beam with rafters to eliminate the bottom part of the truss (is this called post and beam? I'm not sure of the terminology). That would allow me to use shorter walls and still get the height I need.

So, does this make sense? Why do people use trusses in the first place? I'm learning as I go here. I don't want to hire it done, partly because I can't afford it and partly because I won't learn to do thing for myself unless I "just do it!".

 

[MarkV]

Danny,
The big question is how large of building do you want. Roof trusses are normally used so that you can span a larger area than you would be able to with conventional lumber sizes. Let us know how wide and long you want the barn to be and we can give you an idea if it is practical with out trusses.

MarkV

 

[Mosey]

MarkV - I'm planning to build a 22 foot wide by 24 foot long building.

 

[DocHeb]

Trusses are less expensive than plain timbers when used to span longer distances. They also function as collar ties to prevent the exterior walls from bowing out. You could use dimensional lumber for rafters, but collar ties (ties parallel to the floor that restrian the exterior walls from bulging outwards) would still be required. There are many types of trusses beyond the simple truss. Some, like a scissors trust, allow for greater headroom in the building. Others, like attic trusses, allow for load bearing floor surfaces upstairs. Trusses take less time to install than dimensional lumber rafters

 

[mikim]

<font color=blue>to eliminate the bottom part of the truss</font color=blue>
you can't do that ---- picture your rafters leaning against the center beam and braced on the top plate. without joists running from wall to wall to keep them tied in, your walls will be pushed out of plumb by the weight of the roof pushing down and out on the walls. A few years ago I helped a friend put up a garage with 10' walls - when he priced the difference between stick building the trusses or buying them - the trusses were each $10 more - not enough to warrant the time and trouble doing it ourselves. And the manufactured ones I'm sure were better than we coulda built.

mike

 

[BillG_in_TX]

Here's a <A target="_blank" HREF=http://www.cheshirerooftrusses.co.uk/roof_trusses.html>link</A> to a page with various types of trusses pictured. Surely not every kind, and you probably wouldn't want to get them from Cheshire./w3tcompact/icons/wink.gif

 

[MarkV]

Danny,
A roof that wide can easily be build with convention sized lumber. Your rafters would be cut out of 14’ or 16’ boards depending on the pitch and the size of the eaves you want. For a roof rated at 30 psf live load you could use 2x6 southern yellow pine on 16” centers or 2x8 on 24” centers.

I think where you will run into a problem is the length of the building. To build a roof with out ceiling joists (the crosspiece from the top of one wall to the top of the opposite wall) or collar ties (like a ceiling joist but attached above the top of the wall to the rafter) you need a structural ridge beam. A beam 24’ long will be hard to work with and expensive. It would have to be an engineered beam (laminated lumber) which are built to a size their computer figures out based on you building plans and area snow loads. You could get around this but it would require and interior post to break the 24’ span to shorter lengths and that is what most are trying to avoid in a barn.

That is a rather simplified explanation so if I was not clear enough for you let me know and I will try again./w3tcompact/icons/eyes.gif I think as you research farther you will find that trusses will be the most economical way to build what you want. There are also trusses made that the bottom cord (carpenter word for the piece across the bottom) rises to a high point in the center (like the roof does) if that would help meet your height needs.

MarkV

 

[Von]

Danny, I built my shop using Scissor trusses and have 8' walls and have a hieght of over 12' in the center. And have an 8' overhead door to get in. My shop is 24' x26'. I don't know if that will work for you or not, but its an idea.

 

[yooperdave]

Hi Danny,

You have a couple of choices here. For maximum headroom, use a structural ridge beam with a very significant post at each end. The beam would either be a glulam or a steel wide flange section.

A much simplier solution would be to use scissors style trusses. The bottom chord pitches up to the ridge at approximately 1/2 the rate of the top chord. By all means, use a truss plant to engineer and fabricate the trusses. Member sizes, connections, lateral bracing, loading, etc. should not be guessed at by someone with only good intentions as qualifications. Your building should be safe and reliable. I hope you can afford to build your building right.

Good luck

Yooper Dave

 

[Mosey]

Thanks for all the info. Everything you folks said makes sense. The scissors truss sounds good, but only gives me the height I need in the center. I need the 14’ height to start about 3’ in from the edge of the wall (it’s for clearance for a car lift, which will be used to lift full size trucks and tractors). Actually 13’ would be probably be enough. My suburban and pickup are both over 6’ high counting the roof rack and I want to be able to lift it so the bottom is 6’ off the ground so I can walk under it. My Boomer is not quite as tall, but there’s always a chance I could get a bigger tractor someday, or my neighbor might want to use the lift for his tractor, which is a bigger tractor. MarkV, you’re right, I don’t want any center post in the way. The engineered beam sounds too expensive.

I started out planning to build 14’ high walls, but when I went to talk to the building codes guy he said I can’t have wall that high with having them engineered, which sounds expensive to me. He was going to check on whether 12’ walls were OK and get back to me, but hasn’t yet.

So, any recommendations on how to proceed without getting into too much money? Or, is this something that can’t be done without spending a lot of money on a engineered design? Thanks.