roof sheathing w/ 24" centers

[yeldogt]

The older 1/2 of my studio was built back in the 60's and I just discovered 24" on center roof rafters. Have always noticed waves in that roof deck -- it's not bad .. but, obviously not flat.

What's the correct size roof sheathing for 24" centers?

The space is finished -- so the roof framing is hidden. Recently fixing one of the soffits I noticed the 24" spacing of the rafter tails. What a dumb way to save some $$ ... now I have to rip the whole thing apart.

My plan was to replace both of the roofs next year and fix the dips. Originally thought about ripping off the old sheathing -- new sheathing -- new shingles.

Some have suggested covering the whole roof with metal after shimming with horizontal lath across the roof. Sounds iffy.

 

[red61cj5]

I have seen 3/4 tg plywood used in that situation, not ideal but probably will take the waves out.

 

[The Tool Tyrant]

Standard truss spacing is 24" o/c, and depending on the span, a lot of conventionally stacked roofs are either 16" or 24" o/c. 1/2" OSB has a panel index of 32/16 which means it is designed to span 32" on a roof or 16" on a floor (although I would do neither).
You use the word "deck"...is your roof flat or pitched? What type of roofing material and how many times has it been re-roofed without a tear-off?

 

[ddawg16]

The original part of my house is 24" OC rafters. But, has 1x6 (3/4 x 5.5") boards spanning across.

My addition has 2x12 on 16" OC. I'm using 1/2 CDX. In the areas where I mated my existing roof to the addition, I used 5/8" plywood. The height differeence between it and the 1x6 boards was almost impossible to detect and it gave me a very nice stiffness across the 24" span.

NO WAY I would use OSB for roof sheathing. It's fine for walls...but not roofs....even though some say it is.

And you don't use T&G for roof sheathing.

 

[jeepboy4life]

Growing up roofing with my father (33 years in the union) when ever we replaced roof decking we always used 3/4" ply wood. It will take out the waves that you see and will look alot better when it is done because of it.

 

[yeldogt]

This is a standard looking pitched roof. It was originally built as garage space. 34x36. My guess is it's plywood -- they used plywood for the eaves. I don't believe it has another roof under the current -- simple 3 tab on there.

So 3/4 plywood will span and fix?

 

[Falcon67]

7/16" OSB on the shop, no problems after 6 years.

 

[Pack Rat]

IF they used plywood for the roof deck did they put in the plywood clips between the rafters?

 

[yeldogt]

IF they used plywood for the roof deck did they put in the plywood clips between the rafters?

I have no idea -- this is from the 60's and it's all covered. I can see the slight wave across the roof ........

 

[NUTTSGT]

Around here 1/2" OSB with clips is common for 24" O.C. trusses.


If you are going to replacing the sheathing and shingles at the same time, I'd suggest tearing the roof off in sheets. While it might take a bit to get going, after that a sledge from underneath can knock the panels loose. Two guys carry them to the edge and toss in dumpster or trailer.

Once you get a few sheets off, start replacing them but give yourself room to work. Beats the hell out of trying to strip shingles one by one.


EDIT: BTW, moving this to the General Garage Discussion since it's dealing with construction.

 

[T_R]

I have 7/16" OSB 24" OC trusses on my garage roof. It's been fine. I'm in Maine, there has been 4-5 feet of snow up there at times when I didn't have time to roof rake. If it was going to fail it would have by now.

23/32 would be better of course but it's more expensive and the sheets are heavier to haul up a ladder if you are doing it alone like I was.

 

[forAK]

On an almost 60 yr roof and it's starting to get wavy, sounds like a pretty good deal. Considering all of the hold and cold cycles it went through, the glue will break down. As noted above, that's all I ever see up here with ton tons of snow on it. 7/16" with the clips works great.

 

[Pack Rat]

If they are rafters instead of trusses you could also have some sagging rafters.

 

[yeldogt]

It's rafters -- not truss. While I have not put a level on it ... the ridge looks straight and horizontal.

I'm a 16" and plywood guy

... yes built in the 60's .. 50+ years old. I was built in the 60's .. it should not sag.

 

[rnscustom]

Last I did was 5/8" with clips or 3/4" no clips , no 1/2" allowed and no osb period , but times have changed

 

[Toolfool]

If you're getting sag between rafters you should check to make sure you have proper venting for the roof system.

 

[rnscustom]

Last I did was 5/8" with clips or 3/4" no clips , no 1/2" allowed and no osb period , but times have changed

That was on a 4 pitch , probably different on steeper pitches

 

[Randy in Maine]

I used 2x6 trusses 16" on center and 3/4" "Advantec" on top of that.

My wife's next husband it going to thank me that it was way overbuilt.

 

[yeldogt]

I used 2x6 trusses 16" on center and 3/4" "Advantec" on top of that.

My wife's next husband it going to thank me that it was way overbuilt.

Looks like the Zip panel without the covering.

 

[CTyankee]

What size are the rafters?

 

[yeldogt]

What size are the rafters?

No idea -- covered with drywall. I have never noticed any bow from the side. Just the wavy deck in-between the rafters.

It never dawned on me that they could have been 24" centers.

 

[ItsNemo]

We're a new build in Canada and have 7/16" OSB on 24" centers...meets code. Although in retrospect if given the choice I'd have paid extra for 1/2" plywood.

 

[BillK]

My house was built in 1978. 1/2" plywood on 24oc trusses. It has sagged a little almost since new. The original roof lasted 33 years. We ripped it off and redid it and it will be fine for another 40 years.

 

[The Tool Tyrant]

Speaking from 32 years of framing (past life) custom homes, I used to favor plywood over OSB, but plywood got worse and OSB got better. The only 1/2" plywood I would consider is 5 ply...never 3 ply. A 1/2" OSB roof is stiffer than 1/2" 5 ply. It lays flatter and handles moisture better. Putting 3/4" T&G on a pitched roof is like paying for a **** job for a woman with 38 double D's...that's just crazy.

 

[theoldwizard1]

Speaking from 32 years of framing (past life) custom homes, I used to favor plywood over OSB, but plywood got worse and OSB got better. The only 1/2" plywood I would consider is 5 ply...never 3 ply. A 1/2" OSB roof is stiffer than 1/2" 5 ply. It lays flatter and handles moisture better.

I never knew you could spec ply count on plywood !

When my son had a new roof installed, they replaced the decking (so they could add/replace the insulation between the decking and cathedral ceiling). He was told 7/16" OSB was "standard" with 16" O.C. He paid a couple hundred dollars extra to go with 1/2" OSB.

 

[jkeyser14]

Our house is 7/16" OSB on 24" centers. Bouncy to walk on, but no visible sagging.

 

[RocketScott]

Speaking from 32 years of framing (past life) custom homes, I used to favor plywood over OSB, but plywood got worse and OSB got better. The only 1/2" plywood I would consider is 5 ply...never 3 ply. A 1/2" OSB roof is stiffer than 1/2" 5 ply. It lays flatter and handles moisture better. Putting 3/4" T&G on a pitched roof is like paying for a **** job for a woman with 38 double D's...that's just crazy.

+1

As a framer of 20+ years I've seen more delamination of plywood than OSB.

24" spacing on rafters is standard...and all that's needed. That's what I have on my house and it's not wavy. 7/16 OSB and no clips. I spaced the sheets when I built it. Spacing is more important than the little clips keeping the sheets aligned.

Someone made a very good point about ventilation. That's more important than what the roof gets sheeted with.


Sent from my iPhone using Tapatalk

 

[NUTTSGT]

I never knew you could spec ply count on plywood !

When my son had a new roof installed, they replaced the decking (so they could add/replace the insulation between the decking and cathedral ceiling). He was told 7/16" OSB was "standard" with 16" O.C. He paid a couple hundred dollars extra to go with 1/2" OSB.

The next you go to Menards, stroll over to the plywood. They have both 3 and 5 ply. I believe the 5 ply is about $2/sheet more.