this is probably one of those posts that opens up the floodgate for debate, but pushing that aside. Am I ok using 7/16 osb for sheathing on roof and walls 16 oc framing.
Just would like to know if it is acceptable from a strength standpoint, that’s all.
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Replies
Definitely
For strength it has to be structural grade according to local design conditions and code.
Just make sure that it is not exposed to any kind of moisture, it is much more suceptible to it than plywood and it warps easily.
For roofing in particular it needs to be stamped for that use. This will certify that it at least meets MINIMUM standards.
The main problem with OSB for roofing is that it tends to sag over time, resulting in a rippled roof. Plywood holds up better over the long term.
For walls OSB is fine -- no real sense in spending more money for something else.
On walls, you can use it 24"oc, too I think.
After a lot of searching info, I decided to go CDX, just doesn't seem worth taking the chance. It would be nice to save a few bucks, but I'm not one of "those".
Thanks for input all.
Wow. OSB has a solid reputation of being structurally adequate ... and it recycles waste from wood products production.
and it recycles waste from wood products production.
Maybe.
There are quickgrow forest and clearcut production.
Yeah, used to see trainloads of wood chips headed through our town, bound for OSB plants. Was generally birch, I think, chopped where it fell.
When one is half the price I guess there is a reason for that :)
OSB is fine
I wouldn't hesitate to use OSB for roof and wall sheathing.
Typical framing details are to use 7/16" OSB for roof framing on 24" centers.
I only use 1/2" OSB on roof sheathing, but the APA rating of the OSB does allow for 24" centers
Now the fact that you are on 16" centers, 7/16" would be fine (although I probably would still use 1/2" out of habit).
Just remember, with all sheathing to space the joints 1/16 - 1/8".
Terry
Standard OSB Is Junk
DO NOT USE OSB ON A ROOF! A bad leak and you could fall through the roof. OSB is an inferior product when compared to plywood. The only advantage is the cost, and that is being penny wise and pound foolish if you ask me. OSB is also heavier than the equivolent plywood, which takes a toll on your back. It rots alot quicker when exposed to water, and swells terribly when wet and does not return to size. I was working out at JFK and one of the crews had left extra sheets of OSB out for part of the fall and all of the winter. By spring they were mushy. I could break them with my hands trying to pull a sheet from the bottom of the pile. In contrast, I used a scrap of 3/4" piece of plywood to split firewood logs on, so I wouldn't damage the driveway. Left that thing out for YEARS and beat the hell out of it with the wood, the wedge, and the sledge and it was still in good shape when I finally tossed the thing because we were moving.
If a client insists, I would put OSB on the side walls, but never on the roof, and never on anything I built for myself.
I've seen 3/8 ply used on trusses 32" O.C. and it held up surprisingly well. (Although I'd never do it)
Using 7/16 on 24" centers is common. Whoever said that OSB sags over time is full of it. I've never seen it happen.
Still, I like a minimum of 1/2" on 24" centers. But that's just personal preference.
Using 7/16 on 24" centers is
Using 7/16 on 24" centers is common. Whoever said that OSB sags over time is full of it. I've never seen it happen.
I've seen it happen,
On 24's, we always used clips on the sheets between trusses....
In fact, some inspectors wanted it done.
A bit of a pain as they took up a good bit of space in the nail bag and of course popped off at the wrong time. Kept the long edge sheet spacing though.
gap sheathing
You stated that sheathing should be gapped. I have heard this dozens of time, but how can you do this end to end and not end up getting out of sink wiht your joists or stubs. You have a joist at 8' 16' 24' etc, and not at 8'1/8 inche, 16' 1/4 inch, 24 foot 3/8 inche, etc. ????
The simple answer is-
the panels are sized for the spacing. So, if you don't gap it...............eventually you can fall short of the properly layed out joist or stud.
gapping
Do you gap in both the 8 foot and 4 foot directions?
gap in both directions?
Yes.
I've been framing in the northwest for 15 years and every "production" job uses 7/16 osb on walls and roofs. We frame year round here in the Seattle area and yes, this tan is actually rust. Most of the high end customs use ply, but I swear it's partly because plywood is more "couth" and partly due to the greater return on marking up more expensive material.
We have some of the strictest earthquake codes so we wouldn't be allowed to use sub par materials. The swelling is true but primarily for material left sitting in water. There is a waxy coating applied to some brands that repels the water.
As far as sagging roofs, that is actually due to not gapping. I had some guys sheet some six foot pony walls and they hung some of them so tight they had to come back and remove them. They were warped in like one inch in 16 inch bays.
Most plans now call out ply clips, placed every two feet between rafters on each sheet. They are little flimsy things that make sheetin kind of a pain in the a$$. Once I learned they were for gapping I quit using them as I already gap using 16 penny's. As long as the inspector can see daylight he is happy.
We also use 3/4 T&G OSB for floor decking with the waxy coating. The stuff is so nice to work with you never want to go back. Not only does it require very little persuasion {half the sheets I can kick in with my heel and I never need a sledge} but there is also notches in the tongues that allow water to drain so it doesn't just sit on your deck {did I mention it rains once in a while in Seattle?}
There is obviously times when plywood would be the choice, but 16 inch center walls and 24 inch truss/rafters? Absolutly no reason not to use it.
OSB as roof sheathing
Hi,
I'm having my roof replaced - currently asphalt over wood shingles that are on top of horizontal slats that are at least an inch thick and spaced 5 -7 inches apart - my house is old, so there isn't any sheathing. Insurance is covering a lot of the cost, but I really need to reduce my outlay because I was recently laid off. I'm not trying to do anything tricky and pocket money - the checks will be made out jointly - I just need to save where I can. The bids I have call for 3/8 ply as sheathing since it's not structural as much as just a nailing surface. The average estimate has been about $45 a sheet installed. 7/16 OSB retails for $7.50 and 11/32 ply is about $13 and I need 75 sheets. It seems that those of you who favor plywood think it's better structurally when building a roof, but since it's going over a roof - is there a reason not to use OSB? And as long as I have your attention any recommendations for shingles? or other ways to save? I don't want to nickel and dime whoever ends up doing the work, I just need to make good choices and watch my pennies. Thanks for your help.
3/8" ply is undersized for
3/8" ply is undersized for roof sheathing, unless your joists are spaced 12". The ply will sag between joists. Of course, OSB will tend to sag too, but 1/2" OSB will probably about equal 3/8" ply, and 3/4" OSB would (IMO) out-perform the ply.
As to the shingles, basically shingles is shingles -- you get what you pay for. The heavier/more expensive shingles will generally last longer and look better.
I do hope you are tearing off the old shingles. If not, you are wasting money and time.
But to overlay the existing skip sheathing either 3/8 or the OSB is OK IF you space the osb at edges.. I've done it often, with a prteference for 3/8 ply, because it is far easier to carry up the ladder.
Feel free to ignore what Dan said, since it looks like he did not pay attention to what you were describing for your situation where this new layer of sheathing is not structrual.
Given the age of your house, you may need the existing skip sheathign renailed.
Shingle quality can vary according to region and which plant manufactures your product. OC and JM not top of the line everywhere, IMO. I like GAF and Elk. Tamko is good too. Up in this corner of the country we see a lot of IKO.
Filling out your profile or saying what your general location and climate is can help you get the better advice for your location
Yeah, I missed the point that it would go over skip sheathing. (Of course, this assumes the skip sheathing is in reasonable shape and will survive the tear-off.) Over sound skip sheathing either 3/8" ply or 1/2" OSB should be fine. As Piffin says, the OSB is much heavier, and that may add labor costs to offset the price difference of the two. But if the supplier will deliver it onto the roof (which depends on the supplier and the accessibility of the roof) it probably shouldn't add much to labor.
paul
there is no profile to fill out.
Ah, so they did away with that valuable item, eh?
plywood is an old wives tale. osb is better.
3
care to expand a bit?
I am a framing contractor in the coastal SE,have been for years. I have never seen osb "break apart in your hands". It holds up better to weather durring construction imo than ply. I am framing a big fancy plywood house now that has got wet litteraly a cpl times. the ply is delaminating all over the place.Above all, I would never use plywood as subfloor in favor of one of those advantec like products. I have seen that stuff in standing water for days with no effect. jmo.
yes...
but don't confuse tha wannabees with real Advantec
Advantec isn't OSB...it's a completely rengineered product...superior to ply and osb
osb sucks, that's why it absorbs water
the wax coated shid just delays the process of sucking
Advantec is not wax coated , it uses special glues
and you pay a premium price for it
we use it for sbfloors and 5/8 t&g for roofs
usually 1/2" cdx for walls
right
I was talking specificlly about advantec, just didnt want to sound like a rep for it or anything. we also use one of the wannabees alot called structural gold. not nearly as good but but still better than that dry ply crap. even if plywood is better, people who over exaggerate how bad osb is have always seemed silly to me. its fine.
You've maybe never seen really bad OSB.
osb
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