cheapest way out for polebarn roof?

[mopower440]

Paul, what are you speaking of when you say 'slim lumber'? the trussess are made to use 4 foot apart, wich that shouldnt matter because the perlins are what the metal roofing will be screwed to, and i will mount the perlins 2 foot apart..?Just wondering where im going wrong?

 

[Molerj]

I am assuming that you are putting the 2X4 purlins on edge, right?

 

[mopower440]

on the edge?

 

[rambler]

Sorry, you aren't going 'wrong'. /forums/images/graemlins/wink.gif

Things have changed a lot along the way, I believe you have 4x6 posts on 9.5" centers, which is pretty wide. The rafters will be 4' apart, wich won't match up with your posts, so the double 2x10 headers will have to take the load. All fine, but you are streaching things out. I think it's designed to your goals, so not 'wrong'.

Then I thought you were talking of using 1x4 perlins. I think _that_ would have made your roof quite flexable. /forums/images/graemlins/wink.gif If you are doing 2x4, esp on edge, then the roof will be much stiffer than I was thinking. This is what I was rolling over in my mind, thinking you were using 1x4s.

A friend of mine just had a shed almost exactly your size built the past month. He took lots of photos along the way. But here in Minnesota we have to build for 40-60 lb load, while you are probably aimed more at 20 lb load, so things look a lot thicker on his. /forums/images/graemlins/smile.gif Just had a mini blizzard today, only 5" of snow, but 35 mph winds. Only a glimpse of things to come...

--->Paul

 

[biron]

Is there any pictures of that Mn pole barn. What about condensation off the metal? I used metal for my roof on the wood pile and the thing darn near rained.

 

[chucko]

If you are going cheep then why are you not getting trusses right from the truss plant? Do you like to just pay lowes a mark up?

 

[SteveBenson]

The purlins need to be strong enough to span the truss spacing. Like others have said, you should post the general area you live in. From what I have seen around here (with a 40 psf rating), this is how people set their purlins (just observations).

Truss spacing:

4' - 2x4 flat, 2' OC
6' - 2x4 on edge, 2' OC
8 - 2x4 on edge, 2' OC
10' - 2x6 on edge (sometimes set between truss using joist hangers), 2' OC
12' - 2x6 on edge, 16" OC

I have a barn with 10' bay, trusses 5' OC, and 2x4 purlins laid flat 2' OC. The barn is built to code in this area. 5' is the greatest span I've seen using 2x4s laid flat.

Also, you trusses do not have to be at the poles only. They should be placed at every pole, but many people place intermediate trusses too. Your girders just need to be designed to handle them. If you have no intermediate trusses you don't need real heavy girders, which can be a cost savings. This would be more true in the South that has small or no snow loading requirements.

8' pole spacing w/ trusses 4' OC, double 2x12 girder, and 2x4 purlins/girts 2' OC seem to be the standard around here.

 

[shvl73]

Sounds to me that you're doing things correctly, assuming the trusses are designed for 48" O.C. as per local code. The 2x4 purlins 24" O.C. is the best bet, you'll appreciate the strength it give the 29ga. roofing if you ever have to be on the roof for a loose screw or whatever. Galvanized roofing is fairly durable & easily recoated if it ever starts to rust however, have it delivered just before installation. Galvanized roofing can develop a white rust corrosion if allowed to set stacked during times of high humidity or rain & it doesn't come off easily. Once installed it is no longer an issue.