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Old 07-28-2014, 05:43 PM   #1
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Roof Decking


I am presently building a 1200 sq house that is concrete block and brick on three sides with a two by six framed front wall and will use roof trusses. For the roof decking I want something better than the standard 7/16 Osb commonly used in my area of southern middle TN. I am also considering using 26 gauge metal panel roof. My idea is to place two by fours on two foot centers across the roof trusses then put the Osb on top of that. If I then use the metal panels I will have something to screw to besides the mushy Osb and if I use shingles it will be much stronger also. I will install these two by fours myself so labor cost is not an issue. The two by fours will also make overhang lookouts much easier and stronger also. I would like some professional opinions on this idea.

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JM

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Old 07-29-2014, 09:35 AM   #2
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Roof Decking


I used 1/2" (nominal) osb on 16" o.c. rafters with joist bay clips. Roof is tab shingles. I don't have wavy problems.

If you like your idea, I think it'd be faster to put long lengths of 2x4 across on top of the truss then fill in, again on top. Using 2x6 fillers would give you solid nailers for vent gap, if rafter bays will be insulated.

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Old 07-29-2014, 02:41 PM   #3
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Roof Decking


The idea came from wanting to use three foot wide 26 g metal roofing panels. I would never install this type of roof and expect the screws to hold in 1/2 inch OSB, though many builders and roofers do this. By putting the two by course on two foot centers at ninety degrees to the trusses and then covering with Osb gives two inches of wood to hold the screws. Filling in the spaces on top the trusses to make them flush with the two by fours would not be needed for metal but would help a lot for shingles and like you say give a good nailing surface for the decking. Whether plywood or Osb it is recommended to have a 1/8 inch space between all edges of the panels and this would also allow for that using some nails as spacers. You would probably have to beg a contractor to do this as "that ain't the way we do that around here" but since I will be doing it myself I am going to give it a try.
The cost for the extra lumber is very small and unless I am missing something it should work fine.

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Old 07-29-2014, 03:12 PM   #4
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Roof Decking


I myself never specify anything less than 5/8" APA Performance Rated sheathing for roofs. Help keep from having a wave on the roof (being able to pick out where rafter/truss are located).

of course we have a 30 psf ground snow load here.
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Old 07-29-2014, 04:06 PM   #5
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Gary
That's what I put on my roof at my present house I built 16 years ago. The framers whined about having to carry such a heavy piece of wood but they survived. Here in tenn you have to fight to have anything done right. That is why I do everything possible myself. I had rather "waste" a few dollars now in extra lumber or concrete and not have to worry or even do it over later for more money and a lessor result. The way I look at it I am going to save a bundle by building a 1200 sq foot house that will be plenty of space for two people versus four or five thousand like too many build with space they never need or use.

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Old 07-29-2014, 04:13 PM   #6
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Roof Decking


Gary is absolutely correct. I require 19/32" Minimum CD Exposure 1 Fir Plywood. 15/32 inch minimum is required by shingle manufacturers, but it is inadequate, as far as I am concerned. Look at some roofs, you will see the joints telegraphing. I dont like OSB, as it crubles to easily, and it does not hold a fastener as well as plywood. The minumum metal roof I would use is 24 gage steel, or .040 aluminum with a 70% PVDF coating. Steel moves at about 1/2 the rate that aluminum does. As long as your edges are hemmed you are good. 26 gage is too thin.

You don't need the 2 x 4's For a home, I would use a good shingle like the Certainteed Landmark. Snow will avalanche off of a metal roof, unless you install snow birds or rails. Noise is also an issue.
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Old 07-29-2014, 04:38 PM   #7
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Jagans
That is good advice. I don't like Osb either but using 7/16 here is very common for roofs under shingles which I will never allow on my house. A 400 to 450 thousand house just went up next to where I am building and that is what They used on it covered by shingles.As for metal roofs many if not most use 29 g with 26 being the only step up normally available. We do have almost a zero snow load here. I am in southern middle tn very near the Alabama border and we usually get about two two inch shows a year many times melting the same or next day. They have closed schools if snow is even forecast.
The metal roof I am considering is what I put on my present house after 15 years of shingles. I left the shingles on nailed down one by four yellow pine on two foot centers
Pre-drilled the panels on the ground and screwed to the one by fours. These are simple three foot wide 26 gauge PBR profile. I would much prefer standing seam but the cost is
More than double. I definitely think pre-drilling on the ground and deburring the holes on the ground is the way to go.
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Old 07-29-2014, 04:56 PM   #8
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I have put on a couple hundred 26 gauge metal roofs including one on my own house.26G is actually considered commercial.There are no noise issues as many think there are as long as the roof is sheeted.I have screwd many of them into 1/2" osb decking with no problems as long as your are careful how you set the screws.I always try to sell at least 5/8" or ply but the customers know what they want to pay for and they write the check.As long as it's to code I can't argue.Things like this you can't always blame on the contractor you see doing it.
Have put many 26g roofs on pole barns over 2X4 purlins spaced 24" OC.This is standard practice.
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Old 07-29-2014, 06:05 PM   #9
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Mako 1
I agree about the 26 gauge being heavy enough. If I use metal it is what I will use. It may even be OK to screw into 15/32 OSB if as you say done very carefully. But for the small price the two by fours will cost, plus the extra ease of making the eave lookouts and being able to space the OSB on top with wide nailing surfaces I will feel better about the outcome and future longevity. I can't see any downside other than some labor on my part and a little more cost. Without the two by fours I wouldn't use the 15/32 OSB and go to 5/8 OSB or 5/8 plywood which for the amount needed would end up costing more.
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Old 07-29-2014, 06:21 PM   #10
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I agree 100%
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Old 07-29-2014, 06:22 PM   #11
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I have put on a couple hundred 26 gauge metal roofs including one on my own house.26G is actually considered commercial.There are no noise issues as many think there are as long as the roof is sheeted.I have screwd many of them into 1/2" osb decking with no problems as long as your are careful how you set the screws.I always try to sell at least 5/8" or ply but the customers know what they want to pay for and they write the check.As long as it's to code I can't argue.Things like this you can't always blame on the contractor you see doing it.
Have put many 26g roofs on pole barns over 2X4 purlins spaced 24" OC.This is standard practice.
I guess things vary depending on where you are. 24 gage is standard for commercial use here. I guess Through fastened metal roofs on residences survive where you are because of the relatively short panel length used on a typical residence. The old butler type buildings fail at about 11 years due to egg-holing of the fasteners, which are attached to Purlins. I really do not like the idea of exposed fasteners, but if it works for you, then so be it. I would never design one, as they are a first cost type of roof, and I generally deal with buildings of a more monumental nature.
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Old 07-29-2014, 06:45 PM   #12
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Jagans: I agree 100% with your post o but sometimes you just have to go with the pricepoint.I have exposed fastener metal roofs in this area going on 20 years now and have never heard of a leak as yet.I understand how the washers wear and have a limited lifetime compared to the metal.Maybe I've just been lucky.
I have a fewl guys working for me and allow only myself and my lead guy to screw the metal.They will still wear out but correct installation helps.
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Old 07-29-2014, 06:51 PM   #13
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Jagans: I agree 100% with your post o but sometimes you just have to go with the pricepoint.I have exposed fastener metal roofs in this area going on 20 years now and have never heard of a leak as yet.I understand how the washers wear and have a limited lifetime compared to the metal.Maybe I've just been lucky.
I have a fewl guys working for me and allow only myself and my lead guy to screw the metal.They will still wear out but correct installation helps.
No question. If a man wants a green suit, you sell him a green suit. Hopefully, all you use are EPDM sealing washers, Neoprene does not hold up well in UV. You must have good craftsmen and real clutched screw guns
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Old 07-29-2014, 06:58 PM   #14
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Yes EDPM and mayself and one guy I can trust to do it right and a bit of luck which I don't depend on.Funny,just got a call from a guy to go replace all the screws on his roof (his words not mine) that one of my competitors did.Has a bunch of drunks working for him and never on the job.
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Old 07-29-2014, 07:13 PM   #15
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Yes EDPM and mayself and one guy I can trust to do it right and a bit of luck which I don't depend on.Funny,just got a call from a guy to go replace all the screws on his roof (his words not mine) that one of my competitors did.Has a bunch of drunks working for him and never on the job.
What does the EDPM stand for? Also do you guys drill guide holes for the screws? Unless they are pre-drilled and de-blurred don't the metal shavings tear up the washers. I have only installed three roofs on my garages and house but pre-drill and deburr on the ground. Is this a common practice among professional metal roofing installers?

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