In the near future, when I can no longer put it off, I am going to have to replace the sheathing on a small building, a glorified shed. Single story, square and about 24′ on a side. Not being a carpenter I’m not sure on a few points.
I will be replacing 1/2″OSB that has rotted out and never looked right in that it always had a major wave to it. The leaks that contributed, I won’t say caused because IMHO the OSB was trash when installed, have been fixed.
I was going to go with 4 ply 15/32 CDX applied horizontally and glue and nail with all joints blocked. I have been told that 4 ply applied horizontally will give me a good chance of avoiding the wave effect. Studs are 2′ OC. I wanted to go to 5/8″ but was overruled by the cost. Its not my building.
The nail pattern recommended was 4″ at edges and 8″ in the field with #8s. The numbers sounded odd and This was without gluing the ply on. Seeing as that I am gluing everything with PL Premium, good stuff, can I save wear and tear by using a looser nailing schedule? While the OSB held the building up for 15+ years this is a high wind area and I’m wondering if the 4 ply 15/32″ is good enough.
One other thing. Everything I read says to allow a 1/8″ gap for expansion at the edges of the ply but nearly every piece of sheathing I examine on job sites is nailed up fairly tight to its neighbor. Any gaps appear to be accidental and about 1/16″ if present at all. Is this an example of theory versus reality in the field?
Any help would be most appreciated.
Replies
Plywood, or OSB for that matter, should always be applied horizontally (perpendicular to the studs) because that's where its greatest shear value is. On each course the seams or edges should also be offset (not over each other). For example, run one course starting at a corner with an 8' sheet. On the next course (above it) cut an 8' sheet in half and start with one of the 4' pieces and continue with 8 footers. (This is assuming your stud layout falls on center from the corner you're starting from...otherwise, adjust/trim to length as needed).
If you have a nail gun, I'd skip the glue and nail it off as suggested. With the glue, you might back off a little, but I'd guess probably 6" on the edges and 12" in the field.
I've found that the spacing is mostly an issue if it might get wet befor getting covered.
"Plywood or OSB should always be applied horizontally, cause that's where it's greatest shear value is"
Not so Notchman!
Not for walls...and we are only talking about walls. If you run your plywood horizontally as you described, then blocking must be nailed between each stud bay so that the plywood edging can be nailed off soundly. Failing to add the stud blocking, causes the plywood to loose much of it's shear value. It also allows air infiltration.
Here in the Pittsburgh, PA region, homes have had their walls sheathed vertically since the dawn of time. Plywood used as shear walls in the corners of homes sheathed with ridgid foam sheathing for brick veneer framed homes are constructed of vertical panels. They work just fine. And there is no need to stagger panels, which you must do when installing horizontally. Because a panel's 4ft width "breaks" over the center of a stud, there is very little or no air infiltration.
Also, with vertical sheathing, it's easy to nail on when wall is lying down on deck. The plywood sheet can be nailed off in the corner and acts as a brace to keep wall from racking. All other sheets get nailed off and wall is straight (rack free) before it ever gets raised. Don't need to bother with "let-in" bracing.
Vertical sheathing has its benefits.
Davo
Interesting!
I've only seen vertical sheathing on older construction out here and even then only once or twice.
I won't disagree with you because I'm not an engineer, but horizontal sheathing on exterior walls and perp to rafters is just the standard (and I believe code) here unless I'm on an island and don't know it!
The use of vertical sheathing for walls is also considered code. Must be a regional thing....I've only seen a few walls sheathed HORIZONTALLY.
Davo
I know a guy who went through a nasty divorce last year in New York, loaded up his tools and bought an array of cordless/airless stuff and is working his way across the US doing small remodel jobs.
I bet he's either really confused by now or has wildly conflicting, (but strongly held) opinions on everything!
Not to mention T-1 11 .....Jeff Genius has it's limits.....but stupidity knows no bounds
Good point.
Question: If T-111 is being installed as sheathing/siding (single wall construction), what's the minimum thickness, given that you've got dadoes every 6" or so, effectively reducing it's shear strength?
Well Notchman,
I've only seen T-111 installed vertically...how about you?
As for strength, I personally have only used the 5/8ths T-111 thickness; though I believe you can buy it in a 3/8ths thickness as well.
Now, what I'm about to say will probably further blow your mind! Most residential sheathing done today is done so using either 1/2 inch plywood and/or 7/16 ply or OSB. Most of what I see being built is with 7/16 OSB for walls, 5/8s for roofing, and 3/4 T&G for flooring.
Based that 7/16 OSB is being used in walls for residential buildings, I'm sure the 5/8 T-111 is just as strong; even with the dadoes.
BTW. I've read that Canada is permitting the use of 1/4 inch exterior plywood for sheathing.
Davo
No surprises there...I was thinking of that cheap 3/8" t-111.
Interesting thread. If I may add....in my area, all OSB and plywood has arrows pointing up and down surrounding large letters that say "Apply wall panels along strenth axis, top to bottom". That is, it has to be applied vertically. The panels specifically state how to install them. I've never seen horizontally applied sheathing panels on walls...but I'm betting there are locations, situations, and applications that it would make sense.
This has been an interesting subject to say the least. So if ya all would like to get the REAL scoop, go to http://www.apawood.org. What you'll discover, I think, is that everybody is pretty much right.
Plywoods' strength axis IS along it's length, but shear value seems to be effected by nail size and schedule as much as than anything.
As far as the original posters' building, I believe he can take whatever advice he wants here and be OK.
Davo, although you got my fur up a bit with your first response, I guess I have to say thanks for putting me on the trail of the facts. I do think I'll stay with the method I'm familiar with.
"IMHO the OSB was trash when installed...."
What do you mean by this statement?....that the OSB had been left outside and gathered water and expanded before being installed...or are you saying that in your humble opinion, this product is trash? If it had weathered too much before being installed, then that could explain some of the waviness problems.
The OSB was the sheathing...what was this finished off with...vinyl? If so, was the OSB covered in roofing felt before the vinyl siding was installed? If not, this would help explain why the OSB rotted...water does get behind vinyl siding.
Was the original siding nailed off horizontally or vertically. If nailed horizontally, there needed to be blocking between the stud bays. Failure to do this will allow the paneling's edges to bow in or out (among other things) which could telegraph.
If the panels were nailed verticallythey should have little bow in them unless not nailed up properly. Being 2ft OC instead of 16inch OC, there might be some bowing, but not that much.
When you remove your old sheathing, run some string lines along your studded walls and check to see if your wall studs are in alignment.
Most times, sheathing only telegraphs what is already present...a mis-aligned stud wall. If studs are bowed or twisted, and no corrective action is taken, the sheathing is not going to hide this problem. It will infact add noticeably to the blemish. Sooo, before blaming the sheathing for all your problems, please check the "skeleton" first before you begin "re-skinning."
As for nailing schedule...8ds (sinkers) are fine for this situation. I tend to nail 6 inches around perimeter and 10 to 12 inches in the field. I've butted plywood together without no ill effects, but whenever possible ,especially with OSB, I like to space them the thickness of an 8d nail.
OSB can swell horribly. If your sheathing has been rain soaked, I wouldn't use it. Keep it high & dry till time to use, then cover over with paper. Keep waxed side out for this purpose too. (NEVER put waxed side up in roof applications, the reason is obvious...but I've seen people do it...and I've seen them fall.)
LOL.
Davo
"IMHO the OSB was trash when installed...."
I don't like OSB. Never have. Seems like the weaker second cousin to plywood. It's cheap seems to be the only reason to use it. I recognize that it is much better than it was when first brought out. If this first generation OSB got wet your best tool for moving it was a pitch fork. I have seen some newer stuff which was saturated with resin that a local guy builds boats out of. Unfortunately this super OSB is more expensive than the plywood I trust and several times the cost of regular OSB.
The building I was posting about has straight studs but I think that the OSB, this could be first generation OSB, may have gotten wet during construction as each bay is bowed out a good 1/2" more in places. As I remember it was this way long before any roof leaks.
I noticed that no one has commented on the recommended but seldom observed spacing between sheets. It looks like the roof sheathing is spaced according to spec, with small aluminum H extrusions, but the wall sheathing is not. The majority of the joints are tight with maybe 1/32" gaps. Why?
I also have been unable to find and references to how gluing the sheathing would affect nail schedules. Anyone have any ideas?
I did some research and found some recommendations for construction in high wind areas.
http://www.blueprintforsafety.org/GIFS/12.gif
They are pushing horizontal placement with blocking. The parent site:
http://www.blueprintforsafety.org/bluepages/introduction.html
While digging around I found this site detailing hurricane hazards and noting the poor construction practices that allowed much of the damage. A long read but informative.
http://www.colorado.edu/hazards/wp/wp94/wp94.html#climate
I'm in a hurricane zone, and we use 15/32 (1/2") as well as 5/8 and 3/4 plywood sheathing. It depends on the builder, the structure, and the client.
1/2" will pass code, but good builders prefer the 3/4" for the extra strength, and straighter, more ridgid plane. This allows siding to be installed with less chance of waves and better nailing surface. In many cases, the only sheathing that is installed is on corners for bracing. All other areas of the wall studs are covered with ridgid foam panels or asphalt impregnated fiber panels. These are usually bricked walls, and this is just how they do it. If cement fiber or wood siding is used, the entire wall is sheathed.
Personally, I would rip off ALL of the bad OSB and install new plywood. Installing the new stuff over the bad OSB is asking for trouble later down the road.
We install them either way here. Horizontal or vertical is common, and either way is acceptable, and will pass an inspection. Horizontal requires bracing at the seams, but most builders do this without any complaints. The small "H" clips that you see are used for spacing, and to add strength at the joints of horizontal sheathing that fall in between studs. They are the same thing as roofing clips. Code here requires blcoking between studs, so the clips do not get used here anymore unless someone is trying to cut costs and corners, and fall outside of our inspection zones.
I personally leave at least a 1/8" gap between the edge seams (vertical installation), and the same 1/8" gap on horizontal seams (edges and ends). I have seen way too much buckling in my area on sheathing that was tight butted. Because of this fact, I always leave a gap. James DuHamel
J & M Home Maintenance Service