1/2″ CDX Ply or 7/16″Oriented Strand Brd
PlaneWood
| Posted in General Discussion on
Which is best for decking a roof?? I notice the 1/2″ CDX is a little more expensive. Does that indcate better quality?
The roof will have asphalt shingles on top of 30# felt paper. I live in humid and wet south Texas.
My sources for the two are Home Depot or Lowe’s.
PlaneWood by Mike_in_Katy (maker of fine sawdust!)
PlaneWood
Replies
5/8" ply holds them nails much better
Ply is better than osb
Mr T
Do not try this at home!
I am an Experienced Professional!
Ply is better than osb
i know a PE who swears OSB is stronger than ply. OSb does NOt have voids...most ply here does.
Ya, I price 5/8" fir ply for roofs, even my own.
1/2" ply is ok if your framing is 16" OC.. if your roof framing is 24"OC, we always use 5/8 .. in both cases we use plywood clips too
Mike Smith Rhode Island : Design / Build / Repair / Restore
They don't have much of a need for snow load in South Texas, Mike, so the 24"OC is fine if it is 1/2"plywood. Very common down there.
I have used osb on wall sheathing but am not sold on it for roofs yet. most especialy in hot and humid climates..
Excellence is its own reward!
You're kidding, right?
I see osb all the time on 16's, I'll take that all day long over 1/2" ply @ 24
If I build the roof it gets 5/8" fir, @ 16, sorry.
Don't be sorry - be right. An don't cry either
;)
You're not comparing apples to apples. You've got, what?, a sixty or seventy pouind live load requirement over there? Sure I'd want to build it same here but she/he is not here and is only asking about ply vs osb.
Now say that the roof is already framed at 24"OC
Deal with what is - not what you want it to be.
5/8" ply best sure
then 1/2" ply OK
then OSB barely passable maybe.
.
Excellence is its own reward!
Edited 4/6/2003 9:40:40 PM ET by piffin
I thought your initials were PFN, where does Don come from?
View ImageGo Jayhawks
LOL
That line at the top that start's out Don't...
It used to be at the bottom. I meant to use cut and paste to move it but used copy and paste instead. I was erasing with backspace as it posted. It was all gone from what I could see.
Edited now.
I'm still piffin
And they still use 1/2" in the deep south.
;).
Excellence is its own reward!
Gotcha,
hel 1/2 osb is popular in the midwest also. and as for strength, do the same test I have done with mdf, take piece of 1/2" osb and a piece of the same size ply.
Get out your hammer, whack each piece in the center as hard as your elbows will allow. for me the osb allowed the hammer to go threw, the ply didn't.
View ImageGo Jayhawks
Edited 4/6/2003 9:54:26 PM ET by CAG
"Which is best for decking a roof??"
"My sources for the two are Home Depot or Lowe's" (lol)
I answered the first Q, sorry if I went off the map, and I don't care where you are.
Wanna take a stab at the second quote?
I am not crying, how ya been? Did you see spring a week ago, for a day? ;-)
I chose to ignore the second comment about sources of supply. I knew this thread would be all over the map anyway without chasing that rabbit.
You had spring for a day huh? I think we've had two and a half nice days since first of the year. One of those days was a Sunday so I couldn't count it for work. Maybee I'm gettin' grumpy from the mud and the wind and the grey skies.
.
Excellence is its own reward!
Snow? What's that? Been here (Houston) for 15 years and haven't seen a single flake.
So, it sounds like 5/8" cdx ply on 24" centers with ply clips. I'm tying this onto an existing detached garage which has 1/2" cdx ply on 24" centers and clips.
PlaneWood by Mike_in_Katy (maker of fine sawdust!)PlaneWood
piffen.. i know what's fine.... and what's common... 3/8 is fine ... osb is fine.. 1/2 is common...
5/8 with clips for 24" OC
1/2 with clips for 16" OC... that's my standardsMike Smith Rhode Island : Design / Build / Repair / Restore
In Jersey we always use 5/8" fir on the roofs. Rafters always 16" OC. Never seen rafters 24" OC befor stick framing accept for trusses. 24" OC trusses we use clips.
Never used OSB on the roof befor or ever seen it used on the roof although my sheather told me they're starting to use it in some parts of Jersey but it's always 5/8".
I can't remember the last time I used 1/2" on the roof. Probably back in the day when we used 1/2" subfloor and then 1/2" underlayment on top.
Joe Carola
I agree with your spacing to thicknesses of ply.
I grew up in Florida which until hurricane Andrew came through was the holy land of cheaply built houses from low end to high end. Most homes were built with trusses on 24" centers and 1/2" ply for roof deck. Within 2-3 years you could always see the sagging start between the trusses. The sad part was that it was acceptable by the local inspectors.
What works is not always what's right.
Re:
"Within 2-3 years you could always see the sagging start between the trusses. The sad part was that it was acceptable by the local inspectors."
Always great to see a million dollar house with a roof that "waves" at you. In Florida inspectors are underfunded and inspection departments are hen pecked by the builders association. The builders and developers run Florida and do everything possible to keep the building requirements cheap and profitable.
They, the builders associations, fought tooth and nail to prevent adequate inspections and tougher building codes. Only after Andrew pointed out the general sloppy level of workmanship did anything change. Even then only a bit and only for a time. Things are just about back to normal with walls that shake when the doors slam and roofs that better have a return address spray painted on under the shingles if you want to keep track of it in a breeze.
The roofs for my dad's house built in 1968 and my sister's house built in 1984 were sheathed in tongue and groove 1x8 western red cedar. I don't know how many houses were done with that but it was common. But as time went on the lumber yards said it had alot of knots,splits, etc. to were it finally became not available. But I would think that type of roof decking would last forever. I'm curious as to what causes the plywood roof decking to delaminate. Is it too much moisture in the attic? I haven't heard of that being a common problem is this area of Western Kentucky.
Use 5/8 ply @ 16 inch OC or 24 inch OC. If 24 inch OC, use the clips.
On utility buildings, I have used 1/2 inch ply on 24 inch centers with clips and the roof has faired pretty well. But for new construction, I always prefer to use 5/8.
A lot of older (1940 era) houses were originally sheathed with 1X6s. Ultimately, through the years, some of this sheathing needs replaced. If in certain instances, I feel that such a roof requires extensive sheathing replacement, I will in these circumstances cover the entire roof with a layer of 3/8 sheathing. You could even use 7/16 in these instances, but other than a re-cover, I would tend to stay away from 7/16 thick material; that's not to say that homes aren't sheathed with this product...for many are...but thicker really is better, and if you can afford it, use 5/8 material.
I have on occaision used 5/8 OSB, and have seen that product used quite a bit. Though OSB will swell with moisture problems, a properly installed roof should not encounter such problems...I personally have not seen any OSB roofs fail; except for the occaisional shed building that was never shingled properly in the first place.
Plywood normally won't swell or break apart as will OSB when both products are exposed to the same type of moisture problems... to me, plywood is more durable in these instances.
Soooo, to sum it up...stay away from 7/16 for roofing, use 1/2 inch ply if that's all you can afford...otherwise recommend using 5/8 ply or 5/8 OSB...with the ply having a slight edge over using the OSB.
Hey, and remember, OSB has a waxed side, and an unwaxed side. Make sure when installing that the waxed side is installed face-down. You don't want to be walking on a slippery surface all day; especially if your roof has a decent slope on it!
LOL.
Davo
Around here, (western MI ) almost all walls are done in 7/16 o.s.b. roofs 1/2 o.s.b. with clips 24" on center. Some guys go 5/8 on roofs without clips. Almost never see plywood except for floors. I've personally never had a problem with o.s.b. but I probably would be more inclined to add a second layer of shingles over plywood rather than o.s.b.
Yeah, ply is better than osb. Here, its also considerably more money. If you are doing your own home, or money is not a consideration, use 5/8" ply. If you are on a budget, I've seen more homes, starter to customs, decked with 7/16 osb on 24" centers with H-clips than with any kind of ply. If you staple that stuff off good, being careful to hit all the trusses with both legs of the staple and if the roof is dried in and shingled properly, its good to go.
Always plywood and 5/8" ply if the budget will allow for roof sheeting.
now that all the carpenters have weighed in with their opinions on what you should use-------I will give you an indication of the results of their judgement years down the road. Ya see as a roofer-----I get to do the post-mortem on a lot of their decisions----years later.
based on roof work on several thousand roofs over the years
southern yellow pine 1x8's last longest in my climate as roof decking. Of course we can't get THOSE anymore! LOL
Regaurding your original choice between 1/2" plywood and 7/16" osb------I would have to narrowly prefer the 7/16" osb.-----but really thats choosing between 2 un-appealing choices. sort of like choosing between being slapped with a 2 day dead fish---or a 3 day old sack of garbage.
Having torn of A LOT of roofs decked in 1/2" cdx and ever increasing numbers of OSB decks------I notice I have NEVER seen widespread failure in an OSB deck------but we frequently find problems with widespread delamination in 1/2" cdx decks. thats why I would narrowly give the nod to OSB. Anytime we see a failure in an OSB panel---it's an isolated case from a concentrated leak----in which case the 1/2" plywood would also have failed. We frequently find that we have to replace plywood all along the lower eaves ----sometimes 2 courses high----and sometimes the entire deck.
also----we notice real problems when replacing decking ---of ever getting a really flat deck with 1/2" cdx---even with clips. 4 ply does lie a bit flatter than 3 ply----but 7/16 osb lies flat every time-----IF the framing is in the same plane.
Osb doesn't hold a roofing nail as well as plywood-----but then plywood doesn't hold as well as 1x8's! both plywood and osb hold satisfactorily.
So------even though most of these folks are telling you that 1'2"plywood is stronger and more durable than osb----in the real world I find the performance of those 2 products to be exactly opposite what most of these people are telling you.
I don't have an axe to grind either way----I am just reporting what I find.
Thank you.
I think you did a good job of explaining things.
The codes are compromises. Plywood, OSB, and 1x boards all work. In every case one will outperform the others, but there is no best solution.
All are satisfactory when used in accordance to the code and ratings.
Myself, I always use 1/2 BC plywood with rafters on 16" centers.
We have been using 1/2" OSB (we pronounce it OzzBeh :-)) We use 1/2 Plywood wherever the overhangs are exposed. We have had plywood delaminate after just a couple of days. We have never had a problem with OSB. We stick frame all our roofs 24" O.C. We keep the OSB covered until we use it on the roof. We try to keep the plywood on something flat and banded together because it gets so wavy.
We build in the PacNW, so if moisture is going to affect anyone, it would be us. I do agree with the OSB lying flatter. We are extremely anal about how our roof planes, and I do think that that helps.
There are a lot of companies around here that go cheap and use OSB for the entire roof. After about a year, you can look up at the eaves and see the peices showing through the paint. It looks awful. There are some companies that use that LP soffit board for their overhangs. It's the OSB product that has a fake woodgrain on oneside and comes primered. It really doesn't look that good.
I forgot to mention that we H-clip all of our roofs.
Edited 4/7/2003 8:55:05 PM ET by TIMUHLER
Hello again everyone!
I agree as to there being differences between manufacturers of OSB--I've seen some stuff from HD swell from 7/16" to 3/4" after one or two good showers. Also, we were given two different manufacturers' OSB on our last house and told to use one only on the walls because it was lower grade than the other. Go figure!
As far as OSB vs. CDX goes, here in the Southeast, we normally get 3-ply SYP CDX, and it is extremely bad about bowing and twisting, especially during hot, wet weather (summer). We used 5/8" CDX on one house and the same problems were apparent; the only advantage of the extra thickness was it felt stiffer underfoot.
BTW, our codes require (on most houses) 2x6 SYP on a mix of 24" and 16" centers, both spans requiring clips and minimum 7/16" OSB. We have no snow loads, only high wind "uplift".
Thanks for the update. Any experience is always seriously considered. That's why we use 5/8" CDX. Both for strength and perceived, I believe correctly preceived, quality. Used 1/2" CDX in the distant past and did have some delamination problems, usually caused by not being able to get on the deck soon enough, (new work) because of snow or rain. Maybe 3 or 4 sheets out of a 100.
Planewood
"Do NOT" buy your CDX from HD. Or anyyyyyyy lumber for that matter unless its for kindling.
I bought 12 sheets of 5/8th there. Got it to the job and loaded one sheet up top. Laid it down on the roof and put two nails in it to hold it down. Walked on it.....and it felt like I was walking on hollow boards.
Lugged the suckbutt down and back to my truck....Checked all the other boards and they were the same.....returned em.
On my way to the "lumberyard" I passed anothe HD....went in to check out their stock....Same crap.
Be carefull
Namaste
andy
"Understanding yourself is like trying to bite your own teeth"
Alan Watts
http://CLIFFORDRENOVATIONS.COM
Hi, Andy-
Amen. Different qualities of OSB out there. Some has voids and delaminating right off the stack. Find the good sh*t and ask for it by name.
Be well laminated.
Ken Hill
I've been a framing carpenter for 15 years, and a spec. builder for 10. I come from a family of carpenters and we didn't take to OSB right away.
But we've been using it a long time now, and I must say it lies nice and flat every time. I cringe whenever I have to use that wavy #### CDX.
Along with clips, space that OSB with a light 1/8" at the ends and you avoid edge swelling and get a nice flat roof every time. 1/2" on 24oc works just fine. Splurge if you want to on the 5/8.
Also, it seems only some of us are forced to live in a world where price matters.
OSB is heavier than plyboard so it is a little harder to carry and install. For shear panel and roof I prefer CDX ply. OSB swells much more, so you have to space it at least 1/8" between sheets.
Off the subject slightly, My sub for Gypcrete would much rather see OSB for a subfloor because plywood delaminates often and a thin slab will fracture invariably over delaminated plywood.
Last fall I had some 1/2 inch OSB off cuts I put down in the mud by the walk to lessen the mud-tracking inside. Been 5 months in the snow and mud. Can't believe it has yet to fall apart or warp.
When we used to use 1/2" cdx we would spec 5ply fir. This is getting harder to find , but even 4ply fir is much nicer than alot of the 3 or 4 ply pine that is out there.
Mr T
Do not try this at home!
I am an Experienced Professional!
Hi All,
After reading this thread all the way through, I noticed that no one said or even mentioned "ADVANTEC" sheet goods. It's a form of OSB, only with an adhesive that's far more superior than the original OSB. It's so superior such that it can be submerged in water for extended amounts of time and it won't delaminate at all. The sheathing comes in 1/2",5/8" and 3/4" to suit any situation.
This product is stronger, cheaper, water proof and has never let me down. The days of knifing out delaminated plywood "bubbles" are forever gone. In your case I would use 5/8" (straight edge or tongue & groove) Advantec sheathing.
I build in the Northeast, so I don't know how available this product is in your area. The manufacturing company is Boise-Cascade and is used widely here in the N.E.
I was a little surprised that it wasn't mentioned earlier, has any one heard of this , and if so,what are your thoughts on it?.....................Jules
ADVANTEC ---
All I have heard about it is good.
jules, we're a mix & match company.. Advantech 3/4 subfloor, 1/2 cdx wall sheath, 5/8 cdx roof ply....Mike Smith Rhode Island : Design / Build / Repair / Restore
Jules,
Do you know offhand what you or anyone pays for the 1/2 Advantec, and/or the 5/8"? We pay around $5 for the 1/2 (7/16") OSB.
Hi Tim,
Prices range from $8- $14 on 1/2" and 5/8" but again I think that the price is irrelavant for what it does. "cheap insurance " as they say.........Jules
Timuhler,
You pay $5 for 7/16, not 1/2". For roofs you can get OSB from your lumberyard in 7/16, 1/2 (it is a true 1/2) or 5/8. The big box stores might not carry the 1/2". Be careful with that, I know a lot of guys that use 7/16 on 24 o.c. thinking it's the same as 1/2". OSB does come in a true 1/2" version. That little 1/16" does make a difference in stiffness.
Pip
Jules,
I hadn't heard of the Advantec. I'll ask my salesman about it.
Thanks
Pip,
I know what you mean about 1/16" being a big deal. A long time ago (in a galaxy far far away) I used the 2x12's that were supposed to be the vaulted hips as my cutting station. I only scored them 1/8", but the lead guy on the job came unglued. At the time (I was 15 or 16) I didn't understand what he was so upset about. Now I know better.
We've always used 7/16" since I started framing and that's been about 10 or 11 years. We've never had any ghost lines show through the roofing and no soft spots or sagging between rafters. We do use a good quality comp though and that might help.
We use a forklift on the job now, and if it was my house I would use Advantec 5/8 t&g. I hear it's heavy, but a great product.