truss spacing

[RebelPride]

I am planning on building a 24 x 24 pole barn, using a metal roof installed on top of 2 x 4 purlins. I am not sure how far apart the trusses should be placed. Some of the posts that I have read show trusses being placed anywhere from 16 inches to 4 feet. What is the correct way to determine their placement?

 

[_RaT_]

If these are manufactured trusses, it will be engineered and the spacing will be given to you based on that engineering. It will take into account loads from snow if any, roofing material and of course span(s). Sometimes trusses are spaced at 24", sometimes more. It depends on many factors including the size and type of wood used.

 

[RebelPride]

They will be enginered trusses, so what you are saying is, they will make them to your specifications, or that they are already built to there specs, and are spaced according to the load?

 

[Glenn9643]

Rick,
What works for me might not for you, but my two shops and houseboat have trusses on 4' centers. Built my own trusses using SYP 2x4. I've also used treated 1x4 for purlin instead of 2x4 and it works well as the metal roof is relatively lightweight and we don't have a snow load problem in the south.

 

[Gatorboy]

<font color="blue"> What is the correct way to determine their placement? </font>

It is based on several factors, for example, snow load, roof material, slope, type of wood, what size wood for chords and webs, etc.

I bought this publication called Designs for Glued Trusses. It was $7 and is full of truss designs to aid you in determining the answers you seek.

 

[Egon]

Go check with the fellow selling you the trusses. You will get all the information you need.

A 24 foot span with a rise of one foot for every four feet of run should be a very common span if that is what you intend on using.

Egon

 

[Nasty135]

Rebelpride, I live in md. and we have had snowfalls up to 16"-18" at times and my barn roof is metal on rough cut 1"x6" purlins with trusses on 4' centers and I have had no problems. /forums/images/graemlins/smile.gif See pic I would think you should be fine.But I'm not an engineer! /forums/images/graemlins/ooo.gif

 

[chucko]

</font><font color="blue" class="small">( They will be enginered trusses, so what you are saying is, they will make them to your specifications, or that they are already built to there specs, and are spaced according to the load? )</font>

Trusses, something I know
You tell them what you want and they will see if it works by eng-ing them on the computer. If they do not work like you wanted they will let you know what works. It is all part of the quote process. Most places do not stock trusses because everyone wants something a little longer shorts steeper...

 

[boustany]

As said, the truss manufacturer tells you what the spacing is. Based on your description, I'd guess 24". If you went with a heavy roof (say tile) they'd probably be 16". Usually wider truss spacings are used when you timber frame the roof.

By the way - ask about attic trusses. They usually do the same span, cost only a bit more, and leave you with loads of useable storage space in the attic. My barn attic has a 12' x 7' x 40 storage space because I went with attic trusses. All I had to do was add a floor, but that can be done later, if you want.

 

[fishman]

Boustany,

The attic truss really intrigues me, as I am in the process of planning a 30x40 shop, and I NEED open attic space. Do you know where to get the plans for a truss like that? How about a picture? I'm familiar with the Fink-style trusses and they look easy to build, don't know about these attic-style trusses.

 

[boustany]

Check your mail, and send send me your email address and I'll send you a PDF of the truss diagram.

Of course, these are manufactured trusses, meaning that, chances are, you can't get code approval without an engineers stamp, but that varies depending on where you are.

Attic trusses are standard fare if you are a truss manufacturer - you just need to know to ask for them and most people don't. For example I just had the final done on my barn, and the inspector commented that he thought it was amazing more people didn't use attic trusses on their houses.

In terms of costs, I can't imagine not using manufactured trusses for a building, unless there were very specific architectural features (such as timber framing) which couldn't be done with them. Even then, in my house I've got coffered ceilings, etc., using manufactured trusses.

For the record, my trusses cost me something like CDN $3,300 (at the time a bit more than US $2,000) for the 22 trussed (one was doubled up because of a stairway). I maybe could have bought the lumber for less, but the time savings, and so on meant that trusses are the all time deal.

 

[fishman]

Thanks Boustany, message right back at you.

Code? What code? /forums/images/graemlins/smile.gif

Anyway, I don't know if I'll build my own, depends on how much the cost savings might be.

 

[boustany]

Zee plans are in zee email.

Anyhow, one thing is, the truss manufacturers have special 'nailing plates' or whatever they are called, so their joints are stronger. Home Depot, etc, sell similar ones but they are nowhere near as robust. Plus, I have never been above to successfully attach the ones that look like a bed of nails.

You could use plywood gussets, but I can't vouch for how strong the resulting truss would be. And thats a pretty important detail.

So, if I weren't using manufactured trusses, I'd go with either stick framing (i.e. birds mouth and all that), or I'd try find a design guide for 'do it yourself' attic trusses.

Still, given the relatively minor cost over the lumber I thinks its a no-brainer to go with manufactured trusses.

 

[johnday]

Rick; No matter how you do it, you've still got to please the Building Inspector. Do yourself a favor and talk to him before you go any further. Some will disagree, but the inspectors job is to HELP you. Thats why you pay taxes.

In southeast Michigan, you require a 40# roof, 250 miles north where my retirement house is, I need a 60# roof. Down here that translates into a 24"OC spacing, up there with the same truss I need 16"OC. Different requirements for different parts of just one state. Now we're talking worldwide on TBYnet, guess what, your getting good advice, but only regional advice. See what I mean?

Good Luck, building can be fun, then again, sometimes it ain't. /forums/images/graemlins/cool.gif

 

[RebelPride]

Thanks for the help everybody. I have got plenty of time to talk to the truss manufactor and inspector. I am just now in the planning stage, and not in a real big hurry. Although if hurricane Frances hits as hard as she looks like she might , I am sure building supplies will go up even higher.

 

[boustany]

Absolutely pay attention to code and get an inspection.

If you read through the code, it all makes sense. Well almost all the times - round here septic systems are sized on the basis of # bedrooms x # square foot x # bathrooms, meaning I had to put a hotel sized system on my lot.

Anyway, what the code is is a bunch of pre-engineered solutions. Use a double 2x8 over a an 8 foot opening and you know it'll support the load, etc..

Just like electrical, it doesn't usually cost more (or much more) to do it right, and the result is better safety, and less rework & fixes (when the roof sags, etc.).