My builder is using 3/4″ plywood roof sheathing that is stamped with a span rating of 40/20. Doesn’t that mean that it is rated to span 40″ in the long direction and 20″ in the short direction? So if the trusses are 24″ oc, that covers the long way, but is solid blocking required every 20″ betwen the trusses? It’s a 12/12 pitch with slate.
“Put your creed in your deed.” Emerson
“When asked if you can do something, tell’em “Why certainly I can”, then get busy and find a way to do it.” T. Roosevelt
Replies
no thats not it, if that were the case every roof ever plywooded would have had to have blocks.
you know better than that, think about it.
i don't know what it means but it cannot be that you have to have solid blocking every 20"
and if that were the case you would be better off turning the ply sheets a quarter of a turn and solid blocking every 40"
It means 40" o/c for framing members when the strength axis is across 3 or more supports when used for roof sheathing, or 20" o/c when used for subfloor.
There is no way they would stamp a span rating on it. You have to go to charts to line up all the variables. Like what live and dead load is your goal?
Floors might call for anywhere from 30-70#/SF live load
Roofs can be required to have from 15# to 110# or more live load requirements.
Then there is deflection - more concern for tile guys on floors than for rooks
But the same sheathing can be used for all of it - so a single stamp would not work
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MIcrazy got it right.
The span rating doesn't give you the design load limits as in a rafter or joist span table, just how far it can span.
A sheet of 3/8" ply may have a span rating of 24/16.... but that doesn't mean it can span 24" oc rafters with a 50psf load.
Comprende??
I probably should have mentioned that those are the maximum spans.
I understood that,
But still means nothing without knowing at what minimum loads
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
The first number is the roof oc span spacing. The second is the floor span oc spacing.
Bob's next test date: 12/10/07
Maybe where you build.For me I do floors to 50# and roofs to 40#
In CO it was floors to 40# and roofs to 70# most parts of that county
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
I don't know what loads those spacings will support. They are the grading numbers that the APA hands out for each species/type of plywood. Bob's next test date: 12/10/07
Thanks Jim. Looks like only people in texas understand what it means. :) This is from the GP web site:
Q: What is a span rating?
A: The span rating indicates the maximum center-to-center spacing in inches of support, over which panels can be installed. Some products feature a two-span rating such as 24/16. The first number represents the maximum support spacing for a roof application, and the second number indicates a maximum spacing of supports for flooring."Put your creed in your deed." Emerson
"When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it." T. Roosevelt
I got the lessons about lumber markings in apprentice school back in the 70's. In all my years, I never met a single framer that understood what the lumber markings meant. Bob's next test date: 12/10/07
In all my years, I never met a single framer that understood what the lumber markings meant.
And in all of mine, the only framers who seemed to even care, I met here.
Imagine that.Occupational hazard of my occupation not being around (sorry Bubba)
I think more would know that visit site like this. One of the key reasons to know and understand lumber stamps is to prevent failed inspections. I learned my lessons the hard way when my guys wouldn't pay attention to the stamps and I'd have to pay for service calls on failed inspections. The plywood stamp was never the issue but there were other issues related to dimensional lumber; species, grades, etc.To me, it was more of a curiosity that I worked with hundreds of professional tradespeople that didn't take enough active interest in their profession to understand something as basic as lumber stamps. I worked with hundreds of carpenters that didn't know that "stud" was a grade and different from #3. Bob's next test date: 12/10/07
So 40/20 is like a little over 2♦ /1♦ ?
Joe H
I was a genius long before I got to Texas. Now, I'm back to square one.
Bob's next test date: 12/10/07
What I wanna know is:
What the hell is FastEddie doing having a house built with a slate roof?
What the hell is FastEddie doing having a house built with a slate roof?
What's the question? Why a slate roof? or why do I want a slate roof? or why do i think I deserve a slate roof? "Put your creed in your deed." Emerson
"When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it." T. Roosevelt
You choose.
What's the question?
Why is he using 3/4" on the roof?
Joe Carola
Becsause the plans call for 5/8" and the gc thought that was a minimum so he went up one size."Put your creed in your deed." Emerson
"When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it." T. Roosevelt
Becsause the plans call for 5/8" and the gc thought that was a minimum so he went up one size.
What would make him think that 5/8" is minimum? Sounds like he doesn't know what he's talking about because 3/4" plywood on a roof is unnecessary. Hope your not paying for it.
Joe Carola
I'm not going to debate you, because i think you're full of hot air. What's wrong with using better material? If the plans called for a 4" thick concrete sidewalk and the gc poured 5" because he wanted to go beyond the mionimum required, would that be bad? never mind, don't bother answeering, I'm happy with what he is doing."Put your creed in your deed." Emerson
"When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it." T. Roosevelt
I'm not going to debate you, because i think you're full of hot air.
And I think your full of sh!t!
What's wrong with using better material?
Why not use 3/4" on your walls while your at it.
never mind, don't bother answeering,
You shouldn't have posted to me.
I'm happy with what he is doing.
That's fine and that's all that matters. All I asked was why he was using 3/4" on the roof when 5/8" is all you need. You said because the builder thought 5/8' was minimum. That answer right there says he doesn't know what he's talking about, that's all. You can put 1" on your roof and walls if you think it's better material for all I care.
Joe Carola
All I asked was why he was using 3/4" on the roof when 5/8" is all you need. You said because the builder thought 5/8' was minimum.
Maybe the GC thought that 5/8 was minimum because that is what the plans called for. It's tough saying not knowing.
Maybe the GC thought that 5/8 was minimum because that is what the plans called for. It's tough saying not knowing.
If he just started yesterday, maybe. Since when is 5/8" minimum? What would make any GC think that 5/8" is minimum for roof sheathing? There are still many people here on this forum that always use 1/2" specked on plans and have no problems. I always use 5/8". When I first started framing it was always 1/2", now it's 5/8" and that's all on the plans.
Maybe he has slate on the roof, but he didn't say that. I asked why 3/4"for roof sheathing, his answer was because the GC thought 5/8" is minimum. How many people here think 5/8" is minimum for roof sheathing and use 3/4", and I'm talking about for shingles not slate........maybe 1 person......
Joe Carola
Edited 6/13/2008 9:23 am ET by Framer
If it states that it's 5/8" on the plans, than thats the "minimum". The GC can go higher but not lower. So...that makes it a minimum....on that job! He doesn't necessarily have to be thinking that 5/8" is the minimum on EVERY job. He could very well been talking about that one particular job. In any event, I don't see why this topic could push anyone into the angry mode. Bob's next test date: 12/10/07
If it states that it's 5/8" on the plans, than thats the "minimum". The GC can go higher but not lower. So...that makes it a minimum....on that job!
Jim,
You know what I'm talking about.Obviuosly if the plans call for 5/8" you can't use 1/2". What GC would use 3/4" plywood for roof sheathing a roof and not use 5/8"? Plans always call for 1/2" on the wall, so will this GC use 5/8" or 3/4"?
Joe Carola
I dont know Joe. All I know is there are lots of people in this world that think bigger is better...thicker is better. There are dozens on this board that think anything less than 3/4 t and g is susbstandard construction...even for a roof! I once laid a small addition roof with 3/4 t &g because I had enough in my barn and I wanted to get rid of it. Yes, the roof was solid but to me, it is a collosal waste of wood and money. When the pigeons walk on 1/2" osb, they don't make it sink it at all so I'm more than happy with that on any roof I own. And I'm very happy with that on rafters that are 24" oc. To me, that if Fine Enough Homebuilding. But, this other guy might have a different point of view. He thinks I'm cheap. I think he's wasteful. Ying and Yang. Bob's next test date: 12/10/07
There are dozens on this board that think anything less than 3/4 t and g is susbstandard construction...even for a roof!
Jim,
That' my point. Since I've been on these forums for the past 6 years or so, I've seen guys still using 1/2" and mostly using 5/8". Like I said when I first started 24 years ago we always used 1/2" on the roofs. Back in 87-88 we started using 5/8".
We never had any problems using 1/2" before and then we went up to 5/8" and still no problems. I stick frame anyway and always frame 16" centers. Whenever I used trusses and frame 24" centers I used 1/2" 20 years ago w/H-clips and now if I ever use trusses we use 5/8" @ 24" centers w/H-clips and no problems.
3/4" on a normal roof (no slate) to me is nuts. 3/4" t&g on a roof is ridiculous. Alot of guys here and other forums will say that plans are bear minimum and don't trust them and always go a step up, for what? How do they know it's bear minimum, are they the Architect or Engineer? They might as well sheath the walls with 3/4" t&g also.
I'm all for framing a building according to plans and whatever is spec'd on the plans, but changing from 1/2" or 5/8" roof sheathing to 3/4" in a normal condition I will never do and don't believe it's worth it.
Joe Carola
amen, brother!
I suppose you don't screw the framing either ;)
NEVER!
Easy Joe, back away from the computor, take a few deap breathes, it will be all right. I feal as you do, but why bother, it's only a forum with people that don't even know what the stamps mean!
Easy Joe, back away from the computor, take a few deap breathes, it will be all right.
No need to step back and take a few breaths. I'm not mad, I'm just shaking my head. I'm all for building a strong house and framing according to plans and changes with the times, but if every time you look at a set of plans and say that everything specked on there is bear minimum and go one step higher and change, where does it stop.
Many things have changed in the past 24 years for me as far as framing. We started out with 1/2" on the roofs now the spec 5/8". I have yet to see or heard of anyone specking out 3/4" sheathing for a roof.
Like I said before, there are people her on this forum that still use 1/2", if 1/2" is good, 5/8" is more than enough. Now some GC wants to use 3/4", for what? If he new anything about roof sheathing, he would know that 5/8" is all you need and changing to 3/4" wouldn't even be a conversation.
Joe Carola
FWIW I have used 5/8ths. when 1/2 was spec'd. the reason was I was seeing a lot of bows and telegraphing of seams and edges through the roof shingles with the 1/2.
Now I may have had a batch of "bad" ply in the 1/2 but for me the upcharge (which I ate) was worth the price to produce the building I didn't have to worry about being used as an example of "bad " construction. This was in the pre architectural shingle days.
They can't get your Goat if you don't tell them where it is hidden.
I have used 5/8ths. when 1/2 was spec'd.
So have I with a couple plans that I've seen. With that said, how many guys will go from 5/8" to 3/4" for roof sheathing?
Joe Carola
I really don't know. Maybe as either you or someone mentioned with slate I might, but I don't know enough about the fastener requirements for slate to really even go there.
I had to go back and read the OP because I wasn't certain that the spacing of the rafter/trusses was given. I have done 3/4 on wider than 24" o.c. spaced supports, but the OP stated it was 24" o.c.
I would most likely have stayed with the 5/8ths. unless the 5/8ths I had been receiving in the recent past was junk.
They can't get your Goat if you don't tell them where it is hidden.
So, what would be best to hang slates?
5/8" or 3/4" or none of the above?
Joe H
Most of the time we try to use traditional rough cut wood, which is a full 1" thick. There alot of info on this on http://www.jenkinsslate.com/messages/.
I had a look over there & seems 5/8" would never be suitable for slate, 3/4" is marginal.
Maybe FastEddy should ask his Archy if he has researched the slate roof properly, seems he has not.
Learned something new again on BT.
Joe H
Hmm very entertaining discussion thought I would poke the hornets nest and add why 24" OC? Most of the time we frame 16OC staked so rafter spacing aligns with stud spacing and studs align with 16oc floor spacing.
Also on tile floor areas we use 12OC .I am not a slate roof expert but it would seem to me that since slate is like tile in that you do not want any flex that might cause a cracked slate. Also slate roofs last a hundred years or more so you are not going to be stripping that roof in 20 to 30 years like a asphalt roof so why not spend a little more on the sheathing seems like money well spent under a roof that will out last your grand kids.
Most , but not all, residential roof trusses are spec'd at a 24" layout and IIRC the OP's roof is designed to use trusses.
They can't get your Goat if you don't tell them where it is hidden.
It's a 12/12 pitch with slate.
That was from Fasteddie's first post. Obviuosly I didn't read that. My bad.
Joe Carola
My first new house had 3/8" plywood on trusses 24" oc. Code required ply clips for that application. 20 years later, I over laid that roof with dimensional shingles. It all still looks great today. It's plenty enough roof even in a snow load county. It's a 4/12 and is functioning perfectly. You know I'm a minimalist so I'm on your side...but if Mr GC wants 3/4...I'm okay with that as long as I didn't price it to lay it at something less. Bob's next test date: 12/10/07
Stepped through some of that 3/8 ply once.
Termites ate the center ply out, wasn't much strength left to it.
Hurt.
Joe H
LOL...I steppped in a big pile of cow dung once too. I learned my lesson fast! I hope you did too...don't walk on termite infested roofs! Bob's next test date: 12/10/07
Funny thing was, there was no sign of it.
It was like the little buggers just slid the middle ply out.
Joe H
There was no sign on the pile of munure either!!!! That is a huge coincidence!!!!!! Bob's next test date: 12/10/07
That was "sign of it" not sign on it.
Termite piles are pretty obvious in framing. but not up on a roof. That ply looked like new, but not so. There's not a house in Calif more than a year old that doesn't have termites somewhere.
I do know what cow pies look like & I didn't have to step in one to find out:)
Joe H
Maybe the GC thought that 5/8 was minimum because that is what the plans called for. It's tough saying not knowing.
If he just started yesterday, maybe. Since when is 5/8" minimum? What would make any GC think that 5/8" is minimum for roof sheathing? There are still many people here on this forum that always use 1/2" specked on plans and have no problems. I always use 5/8". When I first started framing it was always 1/2", now it's 5/8" and that's all on the plans.
Maybe he has slate on the roof, but he didn't say that. I asked why 3/4"for roof sheathing, his answer was because the GC thought 5/8" is minimum. How many people here think 5/8" is minimum for roof sheathing and use 3/4", and I'm talking about for shingles not slate........maybe 1 person......
Maybe these will help
http://www.literacy.uconn.edu/compre.htm
http://en.wikipedia.org/wiki/Prozac
Tsk TSk McMark. I dont' think that is being very nice. Bob's next test date: 12/10/07
Hey Marky Mark,
What rock did you crawl out from under?
Joe Carola
My apologizies to you Joe. i didn't realize who you were. Just another "Framer". The plans clearly call for 5/8" roof sheathing. The gc felt that 3/4" would be better, so he substituted at no cost to me."Put your creed in your deed." Emerson
"When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it." T. Roosevelt
Fast Eddie,
You say, "My builder is using 3/4" plywood roof sheathing that is stamped with a span rating of 40/20", and, "the gc thought that was a minimum so he went up one size"
It's been a lot of years since I was on a roof that was being sheeted, but if memory serves, plywood stamped 42/20 was 5/8".
If your GC is really using 3/4" plywood, I am fairly certain it would be stamped 48/24.
Good point. I will check next time I go there."Put your creed in your deed." Emerson
"When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it." T. Roosevelt
It's a 12/12 pitch with slate.
My apologies because I obviously didn't read that from your very first post. I would agree with the possibility of upgrading to 3/4" for slate.Joe Carola
Why is he using 3/4" sheathing for the roof?
must be he wants to hold a dance up there!
Here is a link to APA and span ratings. They will ask you to take part in a survey but scroll down and you can go to the info page.
http://www.apawood.org/perf_panels/index.cfm?content=app_pp_atr_str2
Much info on this site. It explains grades of ply and types of veneer used in each grade.
Chuck Slive, work, build, ...better with wood