# what roof decking material should i use?



## chrisd11 (May 31, 2006)

I'm building a 2600 square ft heated (3952 total) on one level. The roof has 12-8 pitch and 12-12 pitch. Is it ok to use OSB, or should I use 1" by 8" or plywood. And what are approximate cost differences?


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## robertcdf (Nov 12, 2005)

Around here in Colorado Springs we use OSB almost everywhere.


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## Bonus (Aug 25, 2005)

I assume you are putting asphalt shingles on? Here, too, 7/16" osb is common and runs ~$12, 1/2" ply is common, too and is ~$20. You need to use h-clips between the sheets, and remember, read the package that the shingles come in. For steep slopes you need to put a lot of nails in the shingles. The shingles likely won't be warranted if you put them down on 1"x8". Again, I'm just assuming you're putting shingles down, is this the case?


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## Big Dave (May 17, 2006)

Around here we use 1x12 #4 pine or cedar. I hate osb for underlayment because when the sun shines on the roof at the right angle you can count every sheet. Looks tacky.

Dave.


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## Darylh (Jan 2, 2006)

I would use 1/2" plywood. It holds nails much better than osb.


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## robertcdf (Nov 12, 2005)

Big Dave said:


> Around here we use 1x12 #4 pine or cedar. I hate osb for underlayment because when the sun shines on the roof at the right angle you can count every sheet. Looks tacky.
> 
> Dave.


I have never seen (or maybe never noticed) that before. Although 90% of the roofs I am looking at would have a high quality shingle. Not sure if that makes a differance. I will try to remeber to look next time.


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## Bonus (Aug 25, 2005)

"Around here we use 1x12 #4 pine or cedar" Hey, Big Dave, you use cedar for underlayment? Stuff must be cheap where you are. It grows here and I couldn't afford to use it for underlayment.

Some shingle mfrs explicitly state on the package that the shingles must not be applied over boards only sheet products, so watch for that.


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## Big Dave (May 17, 2006)

robertcdf said:


> I have never seen (or maybe never noticed) that before. Although 90% of the roofs I am looking at would have a high quality shingle. Not sure if that makes a differance. I will try to remeber to look next time.


Your probably right. Now that I think about it I only notice it on cheaper 3 tab shingles.



Bonus said:


> Some shingle mfrs explicitly state on the package that the shingles must not be applied over boards only sheet products, so watch for that.


I have never seen that before but then again i'm not a professional roofer.

Dave.


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## mighty anvil (Oct 5, 2005)

The loss of lateral bracing should rule out board sheathing on roofs for most houses.

The most critical issue in selection of roof sheathing should be its ability to hold roofing nails. According to the NRCA, for asphalt shingles, using smooth-shank nails, plywood and OSB have similar nail pull-out resistance for similar thicknesses. Using ring-shank nails, OSB has considerably more resistance in spite of popular opinion. 
http://www.professionalroofing.net/article.aspx?A_ID=370

OSB and plywood both swell when wet. Plywood actually swells faster than OSB, however, OSB tends to not return to its original condition when dry so it must be carefully protected, especially the cut edges. If you are not willing to treat the cut edges and cover the OSB immediately after installation, you should probably use plywood. Good quality OSB has been getting more water resistant and AdvanTech by Huber is probably the best currently available.

Whatever your preference, I strongly recommend using 19/32", or 5/8", or thicker structural panel sheathing for roofs for its superior nail holding capacity. Using ring-shank nails would be a bonus in high wind areas but it might make reroofing more difficult.

Clips should not be needed for any sheathing 7/16" or thicker on spans of 24" or less, but if they are used, be sure they are the kind that allow for expansion of the panels.


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## b2v (Jun 19, 2006)

Osb On The Cheap. Based On The Size Of The Ranch, You're Not Building A Piece Of Sh!t, So Go With 5/8" Especially If There Is Going To Be Lag Time Until You Have It Roofed. Rain On Osb Would Prove To Quite Destructive.


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