Why is roof sheathing staggered?
blownonfuel
| Posted in Construction Techniques on
Just wanted to know why the osb or plywood is staggered on roofs? Does it have to be?
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It supposedly makes the roof diaphragm stronger.
Personally, I don't really think it does. But that's the accepted norm.
It needs a drink now and then to steady its nerves.
Linear stress on the long axis of the sheet of ply focuses at the end of the sheet.
So any of that sort of stress on the entire roof focuses on the ends of the sheets. Put them all on on truss and the end nails there bear that burden instead of spreading it out.
same with live loads snow or wind load is shared when joints are staggered, but all focus on one truss when all sheets end there. Stagger and a point load is shared with adjacent trusses.
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Thank you, professor!
For our class tomorrow, please prepare for and explain why the steel roof decking sheet layout, on, say, a big new megasquarefootage Wal-Mart, has no staggered joints.
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"A stripe is just as real as a dadgummed flower."
Gene Davis 1920-1985
well, I don't normally give free advice to commercial users, but I can hazard a guess that it is because it is like everything else at Walmart - cheaper.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Not world traveler any more, and didn't stay at a Holiday Inn last night,but....
I have never seen a Wal Mart with a wood framend or wood truss roof, much less a pitched roof.
Could the answer be in the steel bar joist and engineering, or that the roof deck is tack welded to the steel joist ?
The steel decking is stud welded to the bar joists. i have run a few million SQ of ceiling in walmarts. and hand tied lost of wires to the open web jar joists.ML
I was asking, tongue in cheek, to Gene if any of the things were related to wood framing.
I've probably worked on a couple million sq.ft. of steel roofing that he is trying to conect towood framing. I've also hung several 100K sq.ft. of grid from steel joist.
Like Mike points out, different animals, so why are we acting like the six blind men trying to descripe an elephant from only touching one part of it.
It seems pretty clear. There are some parts of the elephant that you shouldn't touch.
Staggering is stronger. After the California earthquake, the plywood failures were at the joints where the nailing was too close to the edge of 2X or plywood. It was rare to see plywood tear down the middle.
Another example is unstaggered drywalled ceiling, the drywall will crack along the joist where all the butt joints meet.
Not according to the people who make and promote the product.
Jeff
sheathing is structural.....roofing is notMike Hussein Smith Rhode Island : Design / Build / Repair / Restore
Mike, I didn't say roofing. I said roof decking.
How different, structurally, is the plywood sheathing (also called decking) on a stickframed roof, from the 20-gage corruged steel roofing welded to the purlins, or to the joists, of a bigbox store building roof.
What are the mechanics there, why do we feel we have to stagger the sheets, fastening at every end and every intermediate support, with a wood structure, when we don't stagger when doing it in steel?
I'm not trying to be cute. I'm just seeing a pretty clear difference, and wonder why.
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"A stripe is just as real as a dadgummed flower."
Gene Davis 1920-1985
wood framing members & plywood sheathing is not equal to steel frame and steel roofing
you said steel decking..... is there another roofing material over the decking ?
and
what are the dimensions of the steel decking ?.... again....not a one-for-one comparisonMike Hussein Smith Rhode Island : Design / Build / Repair / Restore
Steel decking might be something like 22 gage 1.5" depth, 4" pitch corrugation, 36 inch width net of sidelap, lengths maybe around 24 feet, spanning supports at 6 foot centers.
And sure, there is roofing atop it. A membrane roof like one of the Carlisle products, atop fabricated tapered semi-rigid insulation, of a type maybe made by Atlas or Certainteed.
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"A stripe is just as real as a dadgummed flower."
Gene Davis 1920-1985
apa & code says stagger the ply....the panels deflect differently on the ends than they do on the internal spans....
the steel system is designed for a different application...why do you want to try to draw similar performance characteristics from two different animals ?Mike Hussein Smith Rhode Island : Design / Build / Repair / Restore
Thank you, professor!
For our class tomorrow, please prepare for and explain why the steel roof decking sheet layout, on, say, a big new megasquarefootage Wal-Mart, has no staggered joints.
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Because somebody messed up, or doesn't know what they are doing. It shouldn't be done that way. Unless engineering and the laws of physics has changed a lot in the last couple of years.
Because somebody messed up, or doesn't know what they are doing. It shouldn't be done that way.
Can you explain that?
I've set commercial steel and dropped steel decking on it. I can't ever remeber staggering joints on the panels.
You mean ever engineer that has designed a building I've worked for the last 32 years has screwed the pooch?
Hello Piffin,
Help me with the upcoming re-decking of my house, please. The current 1x6 decking runs from gable to gable.
If the aging 1x6 tongue and groove decking on my 50 yr.old ranch style home is getting a 1/2" CDX overlay with specs requiring 16d ring-shank nails. Which direction will they run the sheets?
Thanks,
Bill
Parallel.
the ply should be perpendicular to the rafters/ trusses, or parrallel with the existing sheathing
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Just do it.
Jim are you working for Nike now?
LOL.Staggering the joints in ply is good practice. It might not be a requirement to meet roof load designs but it is for flooring. Flooring requires a minimum stagger of two joists. Sometime back in the 80's I had to send a carpenter in and replace a couple sheets because they didn't adhere to that principle. If you line all the joints up on the roof, and the member is slightly elevated, you won't like the telegraphing that you'll see. It'll still be noticeable with only one joint landing on it but it will be significantly more visible if you line them all up on it. Dont do it! The answer for Gene: Commercial decking is different. They weld the joints and there probably isn't any structural difference in values regarding the joints all lined up and staggering them. There also isn't any telegraphing when they lay the base board and roofing...which really isn't visible to anyone on the ground anyways. Commercial roofs are all ugly with ridges and humps. There isn't any aesthtetic value to them and staggering the joints isn't as critical as an issue regarding the telegraphing. Residential roofs are much more visible elements in the overall scheme of things.
That's exactly right - it's only an appearance and 'good practice' issue:
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Puddle-welded steel deck isn't subject to warping, bowing and unpredictable end joint behavior the way that roof sheathing is.
Jeff
Excellent. Thanks Jeff.
Thanks Jeff...I tried to be concise with Blownonfuel by saying "Just Do It" LOL! Staggering the wall sheathing and running it horizontally on walls also smooths out the framing irregularities but I'll be darned if I could ever get a framer who wants to run it vertically to understand that.
btw ... same deal for floors.
stagger everything ... it's stronger.
Jeff
Buck Construction
Artistry In Carpentry
Pittsburgh Pa
not to mention how all the nails required for the edges of the sheeting would split the 2x's of trusses terribly.besides all the technical stuff it's just the right way;)