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Tool Talk Discussion Forum

Purlin size for pole shed

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Nick R (Wi)

06-04-2006 05:15:03




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I'm planning for a pole shed 24'wide by 32'long that I plan on building myself. Truss spacing at 8' and pitch would be 4/12. What I would like to know is what size the purlin should be if the spacing is at 24 to 26 inch on center apart. 2x4s, 2x6s or etc. This building would be located in Wisconsin with steel sides and roof. Thanks in advance.




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Nebraska Kirk

06-05-2006 20:22:45




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 Re: Purlin size for pole shed in reply to Nick R (Wi), 06-04-2006 05:15:03  
Just a thought, but have you considered a steel building?

I discovered Steelspan Buildings, Inc. and from what I can see they are stronger than a pole shed, easier to construct and are comparable in price.

www.amsteel.com



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John A.

06-04-2006 09:41:01




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 Re: Purlin size for pole shed in reply to Nick R (Wi), 06-04-2006 05:15:03  
Nick, J&I Manufacturing @ Madill Okla. has premade 24 ft steel trusses for $89 ea. After you figure all expensives on building you own It may be more cost effecient to get premade ones, also concidering wind/snow loads in your area. being engernered for that sort of thing. Hey it is atleast worth a call.
Their ad is always in the Texas edition of "Fastline" Their # is 580-795-7377. Later,
John A.

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you

06-04-2006 08:36:09




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 Re: Purlin size for pole shed in reply to Nick R (Wi), 06-04-2006 05:15:03  
dont skimp on trusses, and also consider not only snow load but ad in a good old blizzird with a 50 mph gust or a wet snow load ,the extra truss will make a big difference



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Frank (N.Mi.)

06-04-2006 07:30:50




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 Re: Purlin size for pole shed in reply to Nick R (Wi), 06-04-2006 05:15:03  
I live across the pond from you, and mine has 4' truss spacing with 2X4 purlins.2' on centers,4/12 pitch. This is northern lower Mich. Building is now six years old and I am well satisfied with its strength.



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J.C. IN AZ.

06-04-2006 07:21:02




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 Re: Purlin size for pole shed in reply to Nick R (Wi), 06-04-2006 05:15:03  
As a former "Astro Pole Bldg" Dealer and Contractor I will offer that Astro Spec's are 24" O.C. for a 7'6" Truss spacing using SPF 2"X 4"X10'Lumber. Securely nailing the Tails of the Purlins to each other where they overlap is part of the "Snow Load" equation. Remember that your Roof Steel adds to the Snow Load Capacity of the Roof.Extreme Snow Load areas have to be Engineer Approved and ,although I never erected one the one Extreme Snow load Bldg. I saw had Trusses and Poles 3'3" O.C.and 2"x6" SPF Lumber on 20" Centers.My feelings at the time considering the cost and the Construction requirements were that the customer would have been served better if he had been sold a Steel Bldg.In your case I still would recommend a 7'6" Pole and Truss Spacing and SPF 2"x4"x10' Purlin spacing on 24"O.C. The tails of the Purlins should be soundly attached to the neighboring Purlin. Attach the Purlins to the Truss using 60penny Ring Shank Nails thru the Purlin into the Truss and then angle nail a 16 Penny Ring Shank Nail on either side in a toe nail fashion.This is not a good Roof Structure for a Plywood and Shingle Decking nor is it a good base for an Insulation and Ceiling situation. Using Truss bottom chords for Storage is not a good practice.

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David - OR

06-04-2006 06:34:11




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 Re: Purlin size for pole shed in reply to Nick R (Wi), 06-04-2006 05:15:03  
Just treat the purlins as if they were rafters. You want to know if a 2x4 rafter on 24 inch centers can span 8 feet or not, considering the snow loads in your area. Your local code officials can show you a rafter span table that applies to your area.

According to the generic tables in the International Building Code, a #2 spruce-pine-fir 2x4 2 feet on center will JUST BARELY span 8 feet with zero snow load (basically considers just a 10 psf dead load and a 20 psf live load).

If you assume a 30 PSF ground snow load, then the max span is 6' 8", and the proposed 2x4 will not work, but a 2x6 will.

This assumes the purlins are laid on edge, like they were rafters. Flatwise, obviously, they would be much weaker.

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MidMiGene

06-04-2006 05:53:22




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 Re: Purlin size for pole shed in reply to Nick R (Wi), 06-04-2006 05:15:03  
I have helped build several in Michigan. On a 4-12 pitch roof, 2x4's on 24" centers meet the building code here. You probably have a similar snow load in WI. Gene



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MidMiGene

06-04-2006 05:57:12




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 Re: Purlin size for pole shed in reply to MidMiGene, 06-04-2006 05:53:22  
After going back and rereading your post, I realised my info was wrong. 2x4 purlins are used when the trusses are on 2 foot centers, not 8 foot centers. I think, for 8 foot trusses, you have to use 2x6 trusses and 2x6 purlins, but I'm not sure. Gene



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I've used both

06-04-2006 05:46:15




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 Re: Purlin size for pole shed in reply to Nick R (Wi), 06-04-2006 05:15:03  
2 x 4 will work. You would be happier with 2 x 6.



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IA Roy

06-08-2006 20:20:45




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 Re: Purlin size for pole shed in reply to I've used both, 06-04-2006 05:46:15  
I helped put the roof framing on a 50 x 310' hog building this week. The trusses were on 4' centers and the purlins were 2 x 4 laid flat on 2' centers. The guys on the roof were skittish about the strength of the purlins to be walking on. The biggest guy was only about 170#. I thought it was built a little light myself. Not a lot of snow load here.



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