Roof decking material

[theoldwizard1]

I have 50 year old ranch house in SE MI that needs a new roof. Much of the existing deck is very soft. The entire deck will come off so additional insulation can be added (no attic access and cathedral ceilings).

One roofer offer a choice of 1/2" OSB or for $6/sheet more, 1/2" CDX plywood. For $240 is it worth it ?

I have also heard that 1/2" decking now actually measures 7/16". Is 1/2" (7/16") "standard" decking thickness ?

 

[KMR Construction]

Around here 5/8" is code. I prefer Advantech t&g but CDX works well. I am not a fan of OSB, nails just don't hold well

 

[BigE]

Just had my house roofed. The original decking (1986) was OSB. They replaced a few pieces when laying down the new shingles. I went after them to repair fascia boards before gutters. Several pieces of OSB were structurally sound but had swelled at the edges due to moisture. Based on that experience, I would never recommend OSB as roof decking material.

 

[mrobins297aaa]

they have 1/2" OSB and they have 7/16" OSB thats a little cheaper and thinner so they are different.

there are studies that show that 1/2" OSB is just as good as 1/2"plywood structurally. I read up alot on that few years back when I was building my garage.

I went with the plywood because I think it stands up better to the elements if it gets wet, OSB maybe just as strong but I don't think its anywhare as good as plywood if it gets wet..........just my two cents

 

[treasureseeker]

I had a sheet of OSB and one of plywood lying on my garage floor for a few years that I put down for the oil leaks from my Bronco I used to have. When I took them up the OSB it was no longer a sheet but a bunch of little pieces but the plywood hadn’t aged.

 

[mmhouse]

To confuse the issue further I believe you will find that 1/2" CDX is actually 15/32", not 7/16" (or 14/32"). You can see the actual thickness by looking at the grade stamp on the plywood.

Each sheet should have a grade stamp. APA is the preferred stamp. Other grading agencies may not be as stringent in their requirements. You should also look for 'Exterior Exposure 1' on the grade stamp which means that exterior glue is used so the panels will not delaminate due to rain exposure during a normal period of construction.

For the little bit of extra money I would definitely opt for the plywood because plywood is more forgiving. Under ideal conditions there is little to no difference but conditions both during and after construction are seldom ideal.

I opted for 5/8" CDX (grade stamped 19/32") for my roof and also asked for panel clips to be used to avoid any chance of sagging between joists but this may be overkill.

 

[mrobins297aaa]

yeah make sure they install the panel clips at the seams.........I think thats pretty much code around here.

 

[holdover]

go with the plywood, it is much more durable, OSB might be ok for walls but the roof should have the plywood.. And yes most 1/2" CDX is marked 15/32

 

[ddawg16]

What is the span? If 16" or less.....either one is fine. 24"? Plywood tends to flex a little less over larger spans. Plywood has less swelling issues on the edges....but then again, I prefer to make sure water never gets to the edges...

Here is a good link that compares the two...

OSB vs Plywood

 

[dreamingmuscle]

Put on metal roof and forget the plywood. You won't regret it.

 

[rodm1]

5/8 is a better choice with the snow load we get you might see warping with 1/2. Best to check the code.

 

[NUTTSGT]

I'd find out why the original decking is soft in the first place. Does it have a ventilation issue ?

I myself would probably use the 1/2" with clips as it tends to be sheaper but if it's that close in price, I might spring for the better plywood.

 

[bczygan]

Read all the particulars of your shingle mfg. warranty. This will specify what you must do to have warranty protection. It may specify deck material and installation methods and approved contractors.

 

[bazzateer]

New roof after just 25 years? I'm glad we build houses out of brick and tile over here.