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SubArcticGuy
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# Posted: 13 Mar 2014 03:29pm - Edited by: SubArcticGuy
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I am installing a tin roof on my 16x16 cabin with a 12:12 pitch. I can't find any manufacturer specs on screw spacing for the tin. The sheets are 164" long and 36" wide (1 sheet covers the entire height of the roof). I was planning on installing 1x4 purlins on 16" spacing. I would then install screws on every 2nd purlin. But I am not sure how far apart they should be spaced either horizontally or vertically. I guess I could just count out how many screws they sent me and do the math...but I am curious to hear what other people have used.
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Atlincabin
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# Posted: 13 Mar 2014 05:50pm
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Typically they will send WAY too many screws, enough that you could almost cover the entire roof with screw heads. On my sheets, I put a row of screws along the bottoms and tops every 9 inches. I used two columns of screws up the main part of the panel, one column on the overlap edge and one roughly in the center of the panel. These screws were spaced approximately 24" centers up the panel. My roof is not as steep as yours (5-12 pitch), so I would probably go with a screw every 16" up the panel on a steeper roof. I also spaced the screws on the gable ends closer together (about 12" in my case) just to make sure the wind wouldn't get under the edge of the roof tin. Depending on the snow load/ice dam formation and wind conditions, you might want to modify this a bit.
Hope this was clear enough to help.
Greg
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OwenChristensen
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# Posted: 13 Mar 2014 06:28pm
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I've been putting three screws wide in each sheet and spaced about three feet apart. BUT, if it were to be in a high wind area, I'd put them every two feet apart.
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Malamute
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# Posted: 13 Mar 2014 07:51pm - Edited by: Malamute
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I believe the specs for Fabral 29 ga metal with 5 ribs in the 3' width call for one screw per flat, two in each flat on each end (top and bottom ends), and no more than 36" spacing up the run. I do 24" up the run on everything. I think they like the screws in the flats to be towards the rib, not centered, as it allows the metal to flex and move some when centered in the flat.
There are also different screws spec'ed for different sheathing material. Wood and plywood can use the smaller screws, with a 1/4" head, OSB spec's the larger "type S" screws that have a 5/16 head I believe. They like the overlaps to be "stitched" also, a screw on the rib where they overlap, I do them on every horizontal row.
If you don't follow their recommendations and you have trouble, they may not warranty the roof metal. I think Fabral has info about this in their web site. A sheet with info about it is also in each metal shipment that I've gotten the past few years.
Edit: Link to their site, the screw spacing is a bit below the pattern layout page. 24" seems like the widest recommended spacing. The lift resistance varies greatly with the sheathing that its laid over. This link shows screw patterns and end patters on the metal on about page 4-5. Other types may use different screw layout.
http://www.fabral.com/wp-content/uploads/2013/02/bluebook.pdf
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SubArcticGuy
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# Posted: 13 Mar 2014 08:02pm
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Thanks for the feedback...so I am I going over board with the 16" OC purlins...perhaps 24" would suffice (roof joists are 16" OC).
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Malamute
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# Posted: 13 Mar 2014 08:10pm
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If using 16" spacing, you'd be overspanned for fasteners using Fabrals guide if you only did every second one. I think 24" spacing would be fine, but don't know the snow load specs for the different spacing.
BTW, pre-drilling the metal is vastly easier than not, and makes beautiful straight rows. Having a block of wood below the drill point and a 2x6 block with your knee on it next to the drill point to keep the panels from riding up the bit as you drill saves tons of broken drill bits. I quit breaking drill bits after adopting the knee board and having something under it.
if drilling, separate the stacks into each side depending on the way you want the laps to run for prevailing wind, each will be a mirror image of the other. Double check youe measurements before starting. I saw a house the guy managed to hit a seam in the sheathing every second row, the screws kept backing out in the wind, was a mess.
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chrisser
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# Posted: 14 Mar 2014 12:44am
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Came to the forum with almost this exact question.
The metal roof manufacturer specifies the horizontal spacing - more screws on the edges and less in the "field".
But they don't specify vertical spacing - they just say "80 screws per square". Googled a square and that's apparently 100 sq ft or 10x10.
So I guess I could do the math. Does the "80 screws per square" only count "field" spacing or do you count the extra screws in the edges?
Why don't they just specify a range of vertical spacings that are acceptable? Would seem a lot simpler to me, and if you were using purlins, that's where you'd need to put them.
I'm planning on using sheathing, but I'd like to put in some 2x4s in between the rafters where the screws are going to go (sort of like purlins, but not quite) so where the screws poke through the sheathing above the loft, we won't poke our heads on them. We won't be insulating right away.
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toyota_mdt_tech
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# Posted: 14 Mar 2014 09:00am - Edited by: toyota_mdt_tech
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Just measure and lay them out perfectly, ie vertical and horizontally, all line up. If you stand back and its short of perfect, it looks like fecal matter.
Screws go between the ridges, not on the ridge. Extra around the edges, then the flashing over the ends and ridges. So the cuts can be dont with tin snips, you wont see it.
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Martian
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# Posted: 14 Mar 2014 10:27am
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There are stitch screws every 2' up the lap starting 2" from the bottom, and one beside each rib across the sheet. I also put one on either side of the rib at the bottom to hold it straight. Make sure your screws are holding down the top sheet at the laps. Most of the lifting load is at the bottom; so secure that area really well. Use screws long enough to penetrate the ridge cap down through the rib and into the sheathing, too.
Tom
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morock
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# Posted: 15 Mar 2014 10:44pm
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For my roof the manufacturer spec'd screws only in the ridges and every two feet. I agree with predrilling .... nothing like straight lines. One tip, don't drill both holes on your over lap and line up the panel ends as lining up two holes is a real pain and will likely be slightly off too.
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