By the end of this week I have to make an application for a zoning varience on a pole building I want to build. I don’t have to have a full blown design for this zoning phase, but do have to give a sketch with basic dimensions of the intended building.
My plan is to buy “Storage rated” or “attic” trusses (ie usable for attic storage load), with something like a 10:12 or 12:12 pitch.
My question is what is the longest span I can count on for such a thing…before it ceaces to be cost effective? I’m sure I could get a huge span if I wanted to pay through the nose for it… I’d design my bldg with a span limit in mind.
For example, I’d keep it to 24′ width if trusses over that legnth get real pricy.
Also, is there a truss Mfr trade organization I could reference too?
Thanks.
Replies
Attic trusses can be great things, in certain situations. Expensive trusses, but cheap space per square foot.
Is there a particular size of building that you have in mind? I'd suggest figuring out what size building you want, then figure out how to do the attic from there.
But to give you some ideas to work with - A 24' attic truss at 12/12 is pretty typical stuff. But take it up to 28', and you have to lower the pitch or piggyback the trusses. (Make them in 2 pieces) So maybe a 28' at 10/12 starts to look good. Some truss places can build stuff up to 14' tall, others only 12' or so - It depends on their equipment. Keep the trusses in one piece and they'll be cheaper.
Once attic truses get up around 40' you start having trouble getting them to work. So then you start throwing more wood into it and get into some big bucks. That would probably be a practical limit to work with, unless you have a center bearing wall to help out.
One thing I don't like about attic trusses in general is that the manufacturers tend to stretch out the bottom chord spans to ridiculous lengths. Like 2X10 bottom chords spanning 18' or something like that. I always limit the length to depth ratio to 18 on the bottom chords. You gain some spring simply because you're walking in the middle of a roof truss - Stretch the bottom chord out too far and you've got a trampoline.
Ther are several truss related websites, but they won't do you much good in this situation. The Wood Truss Council of America (WTCA) has a site at:
http://www.woodtruss.com/index1.html
Then there's http://trussnet.com/, which is run by Wickes lumber. They have a discussion board, but it's pretty dead. (Like JLC)
Let me know if you have a specific span/pitch in mind, and I'll see if I can't come up with a rough drawing.
Support your local undertaker - drop dead.
Boss,
Just did a 30' 12/12 attic truss roof, with piggy backs. You're right about the floor bounce. Also, the manufacturers jig must have been off , on the attic trusses. The pitches were'nt the same, up to the bottom of the piggy backs. To compound this, the contractor who installed them ( not me) flipped them inadvertantly off the pile. Took 2 & 1/2 days of planing and shimming to straighten. We are talking variances of an inch, on some trusses. Nice fab. job hey ? I ran a truss shop floor early in my career, we alway rechecked against a pattern during production, apparently these guy don't . It's a shame some folks don't care about Q.C. I'd hate to be the guy that has to sheetrock that thing!
Brudoggie
Surely you jest - Trusses not lining up ???
Must have been your mistake. Trusses are NEVER wrong......................(-:
BTW - What room size and bottom chord size were you dealing with?
Boss,
21'wide room w/4' Knee walls & 8' ceiling, 2x12 joists. Trusses were 16" o.c. These were about the 4 th set of trusses I've laid my hands on , in the 15 yrs, since I built trusses. I'm a big stick frame fan, sorry! Maybe it is just incompetence in my local truss suppliers. Sent Architects plans for a custom lake front home to the supposedly better supplier, for a roof package, a few years ago. Hip roof, lots of corners, and a 600 sf mostly unsupported 2nd story in middle of home, also w/hip. Their response was " you want to do what". At that point I had former boss order up a pile of LVL's, and 2x12 Doug. fir, and cut loose. Managed to field engineer the job to eliminate some support posts that customers did'nt like in their living room. I like parallel chords for cathedral ceilings , because I build in the Great Lakes region, just wish they could be built on a tighter tolerance, but having done fabrication I'm well aware of the limitations. Maybe you have the answers, seeing you're in it daily. Does the oreintation off the pile really matter, or are they just blowing smoke up my ###? Have a good one!
Brudoggie
Brudoggie -
You threw out a lot of stuff in that reply.
21'wide room w/4' Knee walls & 8' ceiling, 2x12 joists
Bad news there - I'd never do a room over 18' 9" with 2X12. (20 to 1 ratio) That would explain your springy floor.
I'm a big stick frame fan
That's O.K. - I plan to start a self-help group for that...........(-:
mostly unsupported 2nd story in middle of home,
I get a lot of those - Mostly drawn by guys with autocad who think they're architects. Sometimes they draw a dashed line in the middle of the basement and write "beam" next to it. That's about all the engineering they know how to do. They expect me to spend hours and hours figuring out how to support these mysteriously floating second floors (for free) and then don't understand why it ticks me off. Sometimes they don't bring in the prints until after the foundation is in, and there's no way to add more footings or pier pads. Definitely one of my pet peeves.
Maybe you have the answers, seeing you're in it daily
Not, not really. Wish I did. The truss industry is still maturing, but it will be many years before there are any significant changes.
Part of the problem is inherent in the construction industry itself. We mostly hear 3 things from contractors:
1. How cheap can you make these
2. How fast can I get my quote
3. How fast can you get them to me
Quality is somewhere around number 10 on the list of priorities. so consequently the plant guys mostly hear that they should build things as fast as possible. It isn't easy to make a quality control program a high priority when everybody's hounding you to get stuff out the door.
Does the oreintation off the pile really matter, or are they just blowing smoke up my ###?
Yes, it does matter. As you've noticed, trusses aren't perfect when they come off the tables. There might be a dip down in one top chord, and a slight crown in the other side. Or the peak may have been shoved a touch off center to get things to fit better. Most plants I've worked at paint the tails on one end of the trusses, and the crane operators know that all those ends should go the same direction.
Guess that's enough B.S. for one day.........
Moody bitch seeks nice guy for love-hate relationship.
All,
Thanks for the tips and feedback
Boss,
Sounds like under 40' could be OK for a single-piece attic truss. I'll probably be more in the area of 32'. For some reason I had the notion of 24' being a cutoff point, so this is good news for me.
I like to err on the conservative side in terms of load ratings though. This is for my woodshop, and the attic is for storage...maybe even lumber storage. Is this kind of weight too much to ask for an attic truss?
I never even thought about keeping the orientation of the stack the same. good to know!
A 32' attic truss at about 9.5/12 should give you a decent room and not be too expensive.
If you're worried about the loading, just tell the truss people how miuch you want the thing designed for. A live load of 40 PSF on the floor is typical. Some use 30 PSF, which I think is too light. You may want to bump it up to 60 PSF or more - It's your choice.
But keep in mind that sooner or later you have to start reducing O.C. spacing and/or using larger chord sizes to make the truss work, and that can get expensive.
If you get a proposal from a truss company, email me. I'll send you my fax number so I can look over their design if you like.
If money could talk, it would say goodbye.
Thanks for the offer Boss. When the time comes I think I'll take you up on that. I'll buy ya a beer in the Tavern for your troubles...
Boss,
Sorry to dump my post job completion stress on you. Contractor who installed the trusses, really passed me a beauty this time! By the way, it was his own personal project. Nice to be able to pay someone to fix your own problems , hey? I was sure that span was extreme. But what does a carpenter know. As for those designer issues, you know what they reply, "it works on paper", love that one. Don't you enjoy solving other peoples engineering deficiancies? As for Self-help groups, I don't think I have time for another 12 step program. Well, got to get another beer. Thanks for the replies.
Brudoggie
I work in the Boise area of Idaho. Whenever I've used attic trusses, if the span was, say 32 ft., they made us have a bearing wall underneath at 24 ft. I don't know about your area, but I'd bet it would call for similar requirements. Instead of using dimensional limber for the bottom chord, the truss companies here have almost all gone to a web design, like a 12 to 16 inch parallel chord truss. But still, the engineers require a bearing wall at 24 ft. I've had both 2x4 and 2x6 walls required, depending on the engineer. Good luck.
Don't know why they'd require a bearing wall on 32' attic trusses, unless they were putting such large rooms in the trusses that they needed it for the floor to work. I've done clear span attics up to 50'.
Maybe it's because "We've always done it that way"
Honk if you hate noise pollution.
I may not be understanding the situation, so forgive me if I'm out of line. How are you going to put attic trusses in a pole building? Don't pole building trusses normally sit 8-10' on center with purlins between them?
Mark
Yes, I am serious. And don't call me Shirley.
Mark,
Lots of pole buildings are built as you suggest. I've also seen them with "normal" trusses like I was suggesting. I'm open to any sugestion as to how to create usable storage space up there. No way to do that with pole barn trusses 8' OC
Any reason I CAN'T use attic trusses for this application?
You can use attic trusses 8' O.C. on a pole barn two ways.
First, place the trusses 2' O.C. and use some sort of header between the posts.
Second, design the trusses for the 8' O.C. spacing. But the trusses may have to be 2 or 3 plies to work.
"Truss me"
Thanks for being here Boss , you compliment the posts. Maybe we can bring this thing back with more like you . [ did you sell your house ?] Keep us updated on that .
Tim Mooney
Thanks for the kind words.
The house hasn't sold, but there's another open house this weekend. We've pretty much decided that if it doesn't sell, we'll probably just move into the dumb think. The realty contract is up at the end of June, and DW is off for the summer. (She teaches) Don't really want a huge mortgage hanging over our heads, but....
Friend of mine just had a nice pole barn built.
About 32 by 60, 12 foot ceiling on the ground floor,
12/12 roof, attic floor rated at 100 PSF for
storing hay. Trusses were 2' OC, bottom chord
looked to be doubled 2x12. 6 foot knee wall upstairs,
about 20 by 60 feet clear space. Probably more
heavy-duty than you need, but around here a 40 foot
barn truss is not unusual. Even seen ones as long
as 90 feet unsupported span for a horse show ring.
A good truss shop should be able to tell you the options
once you decide on the span.
Stray -
I am in the finishing stages of a pole building garage. I considered attic trusses. In my area standard 4/12 truss runs about $45 (30' bottom chord). A 12/12 attic truss (8-0 ceiling) was $245. Easy choice, I put the extra space on the floor. If you're planning on hauling large pieces up and down, I'd sure seriously consider main floor storage.
Also, in my area (Michigan) I see lots of pole barns and looked at a lot when deciding what to do with mine. I'd make sure that you don't have to bump up the pole/footing/header size to allow the load bearing you want. Any time you bump up that, you bump up the cost exponentially.
Freddie
HEY STRAY,
IF A QUALITY BUILT TRUSS IS WHAT YOUR LOOKING FOR .....BUILD THEM YOURSELF
YOU WILL SAVE MONEY AND THE RATIOS ARE ALL TEXT BOOK
CONTACT ME AN I CAN HELP YOU WITH DESIGN
Yeah, thaty's the answer to all our problems - Someone building their own trusses just because someone on the internet told them it was easy and they know how to do it.........
I have actually built trusses for a pole barn before, and with great sucesss. They were only 24' wide, and not attic trusses though. Is there a reference book to point me to for truss design, spans, load calcs for trusses, etc...?
Boss,
I hear where you're coming from ...and to be quite honest w/ you I'd prefer to have someone drop a stack of these off on the jobsite instead. By the time I figure in my labor, I know I'll be over the cost of manufactured trusses. I barely have enought time to build the rest of the building.
"Is there a reference book to point me to for truss design, spans, load calcs for trusses, etc...?"
No - But I get asked that question a lot. Think about it - Why would anyone want the liability associated with such a book?
For some reason when someone wants to build their own trusses, they don't want to hear that it's not a good idea. They can get pertty defensive. I've really gotten a lot of crap over it a couple of times.
Your're right Boss. Go with the pros. Let their engineer design the trusses. drop them at the job site, you set them with a crane. If you have a problem call the truss shop. I've been doing this over thirty years, it's cheaper and better.
Charlie