7/16 OSB roof deck

[John B]

Is all 7/16 OSB equal?
Common practice for a composition roof (in N.Texas) is with a roof deck of 7/16 OSB and rafters at 24 O.C.
Most roofs look fine, yet some roofs show "Sag".
What is going on here? Is it improper installation?
Is one "brand" better than another?
5/8 cost almost double here.

[Ed the Roofer]

Re: 7/16 OSB roof deck

With those specifications, I would be very surprised that more roofs than you notice have problems with sagging or decking deflection.

Do you observe these homes one year later to note these deficiencies, or is this a casual obsevation made immediately following the construction process?

That would be the "Minimum" specifications, which I choose to always exceed for my specs.

Ed

[greentree]

Re: 7/16 OSB roof deck

You guys dont have 1/2" in texas or what?

[Diamond Custom Homes]

Re: 7/16 OSB roof deck

Lots of 7/16" roof deck here also. I spec out 5/8" plywood now, pass on the cost and if questioned by HO inform them that the roof is not a place to do the bare minimum.
7/16" is weak even with h-clips, I hate it.

[KLyons]

Re: 7/16 OSB roof deck

There is 15/32 OSB which is better than 7/16, but not as good as 19/32 (5/8).
Prices out better than 19/32.

I never use the 7/16 stuff, if you can choose materials always go with 19/32.

[panthony]

Re: 7/16 OSB roof deck

It all depends on the APA rating for the material being used. I've always deferred to the rating stamp on the material for example a 32/16 span rating translates to maximum vertical span of 32" used as a wall sheathing and 16" when used as a roof sheathing. There is also the exposure rating for floors, roofs and walls to consider.

[ddolman]

Re: 7/16 OSB roof deck

I would guess that 90% of roofs here are 7/16" osb with 24" o.c. trusses. No problems. It may feel weak when you are walking around on it, but after it is shingled, who cares. You dont ever walk on your roof. It will sag if the roof gets wet before shingles, but that can happen with any osb. That stuff has to stay dry to stay flat.

[sbebuilders]

Re: 7/16 OSB roof deck

OSB versus HomeDepot OSB

I needed to setup a spray booth in my garage to spraypaint my garage cabinet doors. So I went to HD and bougth 5 sheets of

OSB APA 7/16" Span Rating of 24/16 @ $6.75 per sheet.

I thought the price was excellent, becuse I paid $12.00 a sheet for

OSB APA 15/32" STR2 Span Rating of 32/16

from my lumber company for wall or roof sheathing.

After only a week in my garage the OSB I bought from HD for the spray booth was bowed in the middle of the sheet by as much as 3".

The sign below the OSB I bought from HD said it was great for roofing. The sign should have said it was great for sheathing over an existing roof.


You get what you pay for. 7/16" OSB with a span rating of 24/16 is only good for re-roofing your house.

Sim

[Ed the Roofer]

Re: 7/16 OSB roof deck

Hey Sim,

I think it was your site that I got some excellent articles and information regarding the pros and sons of OSB vs. plywood.

If so, what ever happened to the article authored by Georgia Pacific, which at the time, manufactured both products, but the article was definitely in favor of plywood?

I did save the orignal article, but the link to it on the GP site just goes to a main page now.

Do you have any more up to date links about comparisons, newer than 1-2 years old. At last glance, if I remember correctly, their were 6 articles on the pros and cons on your site.

Thanks,

Ed

[Thor M, Structural Engr.]

Re: 7/16 OSB roof deck

It all depends on the APA rating for the material being used. I've always deferred to the rating stamp on the material for example a 32/16 span rating translates to maximum vertical span of 32" used as a wall sheathing and 16" when used as a roof sheathing. There is also the exposure rating for floors, roofs and walls to consider.

Actually the numbers in the "span rating" are for roof and floor spans. Sheathing panels with a span rating of 32/16 can span up to 32 inches as roof sheathing and up to 16 inches as floor sheathing.

If you use the thinnest sheathing possible that still meets the span requirements it feels AWFULLY squishy (that's why most of you go to 19/32" sheathing--which BTW is typically rated at 40/20). Believe it or not, you can get 3/8" sheathing rated 24/0. This is okay (by code, anyway) for roofs framed at 24" or less OC, but can't be used for floors at all.

Thor Matteson
www.shearwalls.com

[Dick Seibert]

Re: 7/16 OSB roof deck

Ed:

Is this the article you were looking for?

[Ed the Roofer]

Re: 7/16 OSB roof deck

Ed:

Is this the article you were looking for?

At first glance, it contains some of the same information disseminated in the article I spoke of, but was not structured the same and did not purvey the obvious belief and bias that the article author espoused regarding the superiority of plywood versus osb.

It was more of an editorial proclaiming the differences and benefits of plywood compared to OSB.

I believe I may have copy/pasted the original article in my thread from about 8-10 months ago, regarding OSB vs. plywood. I will search my threads that I started later today, when I have more time.

Thanks for another article for my collection though.

Ed

[whiskytangofoxtrot]

Re: 7/16 OSB roof deck

Is all 7/16 OSB equal?
7/16 OSB and rafters at 24 O.C.
Most roofs look fine, yet some roofs show "Sag".
Is it improper installation?

As far as I know, pretty much all OSB is manuf'd. to the same minimum building codes.

7/16", 1/2", 17/32", etc...24"o.c plyclipped over trusses/rafters is pretty standard all over the South. As far as installation faults, the "waxy" side of OSB is supposed to be exposed to weather, but I've seen tons of guys flip it down due to it being slick on the roof.

Usually any sags in the roof don't show from the street, unless water got to it before dry-in, and even then unless it dried out really quick, it shouldn't be that bad, but I have seen a few that looked like there was an auxiliary valley between trusses.

Now get up on the roof and start looking across peaks, and if it's a truss roof that wasn't strung it'll look like a windy day on the ocean.

[dmwyatt]

Re: 7/16 OSB roof deck

As far as installation faults, the "waxy" side of OSB is supposed to be exposed to weather, but I've seen tons of guys flip it down due to it being slick on the roof.

Incorrect.

According to the APA website.

[sbebuilders]

Re: 7/16 OSB roof deck

Hey Sim,

I think it was your site that I got some excellent articles and information regarding the pros and sons of OSB vs. plywood.

If so, what ever happened to the article authored by Georgia Pacific, which at the time, manufactured both products, but the article was definitely in favor of plywood?

I did save the orignal article, but the link to it on the GP site just goes to a main page now.

Do you have any more up to date links about comparisons, newer than 1-2 years old. At last glance, if I remember correctly, their were 6 articles on the pros and cons on your site.

Thanks,

Ed

Ed, I updated the page with the correct links to GP, but your right the GP orginal article on plywood versus OSB is no where to be found on their website. I found the same articles as Dick. I guess GP didn't want to be sued for selling OSB, when they don't think it's as good as CDX plywood.

I went to the APA website and could no longer find this report that GP referenced.

APA, 2003, Nail Withdrawal Strength for Plywood and OSB Panels, APA Report T2001-3A

In that report it states:

Stiffness.19/32" plywood is 220% stiffer than 7/16" OSB.
Nail withdrawal strength. 19/32" plywood holds roofing fasteners 46% to 76% better than 7/16" OSB.

Is all OSB manufacted equally......NO
I talked to an engineer at iLevel by Weyerhaeuser and he told me that the OSB in their TJI's can't be bought from your lumber company. According to the iLevel engineer they manufacture a lot of commercial products that can't be bought from your lumber company. If they did sell some of thier high-in products to the general public than you could make your own TJI's. I wish I had a tape recording of his explanation of the different types of OSB, but all in all he said there are different grades of OSB.

OSB with a red painted edge is free of urea –formaldehyde resins
(Red color resins are urea –formaldehyde free)

So what's in the OSB with the blue edge?
So what's in the OSB with the yellow edge?
So what's in the OSB with the green edge?



Sim