Does the code allow metal roofing over purlins? I have seen it often but I thought code required roof sheating. Then metal over the plywood?
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you see it alot down south and when the first hurricane comes , those are the ones that loose their roof.
depends on what code you are talking about. Also, do you mean metal over purlins in lieu of roof decking?
I can't imagine. I just can't imagine.
Up here metal roofs are applied over existing roofs by applying strapping and then the metal. On new they are applied over roof deck that has also had a substantial covering of ice and water sheild for added water proofing.
But no original roof deck? I must have read wrong.
Around here in rural areas of NYS, I see metal right on purlins spaced 24" OC and secured at 24". I looked in the NYS Residental code and it does discuss spaced sheathing. However, it does not define spaced sheathing.
Edited 2/26/2006 8:22 pm ET by bhackford
Imagine, Imagine! Here in the south it goes on without sheathing all the time. Ya just put some diagonal bracing in with your purlins or strapping as its sometimes called and screw it down.
Although, I will say most houses with metal roofs do get sheathing, there are quiet a few around that don't . We never put sheathing on barns, cept for them fancy ( we call em trust fund ) horse barns. They usually get 2x6 t & g for decking.
I replaced a metal roof over just purlins last Dec. that was originally put on in 1947 according to the owner.
Just curious, Why would you think that this would'nt work?
Two primary drawbacks to metal directly over purlins or directly over "skip sheathing" (what I learned to call what is now sometimes called "spaced decking"). The main drawback is that moisture can condense on the underside of the metal and drip down to damage insulation and/or sheetrock.Second is that screws can work loose (a lot depends on local winds, type of wood, and size of screws). When a screw works loose it can leak.I have metal on my home, carport, and shop. Only the carport has metal directly over the skip sheathing and, like someone said, I strapped it diagonally with steel UNDER the skip sheathing. IMO, metal roofing should not be put down in contact with anything that could abrade it.++++++++++++++++++++++++++++++++++++++++++++++++++
Our ancestors killed mastadons with pointy sticks!
When a screw works loose, it will still leak with a solid-sheathed roof as much as with a skip-sheathed one. The betterment is only that you can put down the tarpaper to save some from getting in to do damage.
OTOH, you will not always know that it is leaking so it will do more damage to the sheathing before it is found and fixed.One advantage of metal direct to purlins is that on a steep roof, the chicken ladder is already built in until you get to the last sheet!
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The potential damage to sheathing from a loose screw isn't much to be concerned about here, but in other climates I'm sure it would be. I've been in this dry climate long enough that I forget about replacing rotted soffits, facias, and other stuff that has to be done in places with soggy air.I ripped a roof off last summer that had the origianl cedar shingles from 1922 plus two layers of rotted, cupped, cracked old asphalt shingles. Only the lower 18" or so of the 1x sheathing was rotted. Skip sheathing works the same as a ladder for putting the metal on, same as purlins.
++++++++++++++++++++++++++++++++++++++++++++++++++
Our ancestors killed mastadons with pointy sticks!
My own is on bare purlins at 24"OC over 8/12 pitch
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Shhhh, I aint got no sheathing on neither.
Well dug I was actually thinking of a house some poor fool was trying to make himself comfortable in and just imagining all that wind and stuff blowing from outside.But then again, who am I to judge? I have seen people live under less even here in the upper east (where so many want to pretend poverty doesn't exist).And hell, I know Uncle Jeb is jes fine with his half pint, his coon rifle and the woodstove, so what about that fancy roof decking.No seriously, I was not thinking of sheds.Trust fund barns....LOL..I love any terms that disparage the rich and the wannabes. Hell I rode horses boarded by a friend of mine in a huge barn that had metal over purlins. The horses weren't complaining.Again, I wasn't thinking of barns.
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70229.14 in reply to 70229.8
Well dug I was actually thinking of a house some poor fool was trying to make himself comfortable in and just imagining all that wind and stuff blowing from outside
Dang girl, don't be so hard on us poor dumb southerners just cause we aint got no sheathing. Tha younguns aint froze yet!
Why jus last month to keep my ol wind blown house to a comf' table 68 degrees it cost me 160 dolla's. I'm total electric and my boys...they leave them lights on if ' n I dont stay on em.
I never did see no wind blow through no piece of metal :) Only stuff we got blowing around down here is em lounge chairs blowing off em yankee's wina-bagas when they come a batting it through here headed to Flar-da! :)
Boy where I come from, Illinois, a tornado t'would likely take that metal roof offa yous shack like god opening a can of spinach, rightcher in frunna you.I seen it happen. Pelts, sardine cans and empty Schlitz cans flyin' to the heavens with Vernon holdin' out under the bed, prayin that it ain't his time yet.Don't ask me how I got up here its a long uninteresting story.
I could be wrong, but the way I remeber the load charts, the resitance to the wind load depended only on the nuimber and spacing of fasteners, not on the underlying materials. Tornadoes can tear plywood off roofs too, ya know.
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Man, always someone around to correct me when I'm wrong. If I had a team of y'all around all the time, would I then become a genius? Or would it just be chaos?Yes, you are correct, but my mind envisions a metal roof laying on purlins or bare rafters and the walls coming up to the plate with nothing in between, then the wind whipping through there like crazy.I guess if you have an equal gap on the other side you could just let the wind go through.
Around here it's pretty standard on outbuildings-- garages, sheds, etc., at least. I'm thinking I'd want something more substantial for a house, though.
The plan was to put this on a few barn projects I have coming up. I agree. Not on a house. The code seems to not state a spacing?
As for spacing, the metal panels will have a maximum spacing for fasteners.
"Citius, Altius, Fortius"
Metal Sales has a chart for the spacing that shows it dependent on the loads, the pitch, the gauge of the metal, etc.
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Seems like you should limit your liability by getting an opinion from a structural engineer. I'm thinkin' it would never calc out.
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