Purlin orientation for a low slope roof.


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Old 06-05-16, 09:55 AM
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Purlin orientation for a low slope roof.

Hi,
We live in a half double with a fairly flat roof. Roof rises about 5-6 feet over a 55 foot length. We are going with a metal roof. PBR panels seem to be what to use.

Neighbor wants to do their roof also. Currently our roof looks to be tar paper and theirs is tar paper and then roll roofing laid on top. Making their side about 4-5 inches higher than our side. Seems like purlins are recommended for metal roofing, I like the idea of the metal panels not sitting right on the flat decking and having all that exposure to moisture along all the low points of the panel.

I can't figure out the purlin situation. I figured put about 3 2x4's on our side flat side down to build up to higher than their side. Then one height of 2x4's on their side.

Friend who knows some about home improvement said when he was younger he helped do roofs for a little while and he was taught for metal roofs to stand the 2x4 on the 2" side so it sticks 4" in the air. To me that seems like it would have to be less stable than two 2x4's on their 4" side against the roof.

Can anyone give their thoughts or industry best practices for the purlin orientation, please. I figured I'd find results immediately with google and this forum searches. I must be using the wrong terms, or no one really worries about purlin orientation?

Thanks
 
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Old 06-05-16, 10:28 AM
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I think you're using the wrong terms. A Purlin supports roof rafters.

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It sounds like you want to add to the height of your roof in certain areas?

I have never roofed, but haven't seen or heard of anything like this. If you do want to lay boards across the roof, I would call it strapping a roof.
 
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Old 06-05-16, 11:43 AM
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Hi Handyone, we want to add height but only to one half, our half, which sits approximately 4" lower than our neighbors since they have roll roofing on top of their tar and paper.
I'm seeing for PBR panels its recommended to have purlins by most people, at least what I was able to read online. So for our side we were just thinking we would use more purlins to make it taller and match up with their side. Then we don't have to try and find a way to get their roll roofing down.

Then he told me to stand them on end and now I am not sure what to do.

EDIT: I thought, from reading online, that the boards right under metal roof panels were still called purlins?

I appreciate the response
 
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Old 06-05-16, 12:40 PM
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You arent using the term incorrectly. When used under metal roofing, purlins are often laid flat, nailed over the rafters and/or original decking. The spacing us usually 24" on center, but follow the roofing recommendation.

https://www.google.com/imgres?imgurl...act=mrc&uact=81
 
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Old 06-05-16, 01:15 PM
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Thanks Sleeper. I was picturing the metal roof being individual shingles and not panels.
 
 

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