Educate the moron – plywood differences
OK, here is the setup: I’m shear walling the interior side of my garage (outside is stucco). I’ve been using 3/4″ BC sheathing, and I’m almost halfway done.
Anyway, I make my first Home Depot post Katrina/Rita plywood purchace, and here is what I’m presented with:
BC (what I used before) $31.95
AC……………………….$31.99
AA (hardwood plywood) $26.99!
So here is my question: Can I use cabinet grade plywood (7 ply I think) for an interior shearwall? I know there are no certifications on it – no APA stamps on the face or side. But since this is interior, will that matter since it will not be rained on, nor used as a floor?
It’s such a better price I could get another sheet for what I’m paying for the lesser grades – is it worth it to use only the rougher stuff?
Rebuilding my home in Cypress, CA
Also a CRX fanatic!
Replies
Gee Paul, that might depend on if you plan on using screws instead of nails.
Gee shod, are you a troll?. For a 1st time poster that is probably te dumbest reply ever.
Paul: Really depends on your local codes (aka pickey little assinine pervert beam counterer inspectors), IMO, what you suggest is better.
So what is the sheathing that is on the exterior wall, under the stucco? Is it not already shear paneled? I'm confused; we shear panel our walls on the outside before applying a stucco finish. I wouldn't apply stucco to a building that wasn't braced for shear.
So if it is already shear paneled, why are you applying shear to the inside, and 3/4" at that?
To answer your question, cabinet grade 3/4" plywood is more than adequate as an interior shearwall, provided you install the necessary fasteners.
The heck, you say?
Shearwalling both sides may be uncommon but it is required where high windloads and high seismic risks may exist. I recently finished a large custom in which both exterior walls and interior bearing walls were sheared both sides on two stories. (made for a lot of custom door jambs!).
But, in my experience, shear walls are usually 1/2" or 5/8" CDX, both of which are less money than the OP is preparing to spend. In fact, 5/8" MDO signboard is less and has a smooth finish.
3/4" shear walls on a garage seem really excessive unless it's designed for parking double-decker busses.
And, as you implied, the fastener schedule is probably the most critical element in a shearwall.
I have never run into a situation where it was necessary to sheath the complete surface on the in and the out.
I have provided shear panels, usually 4' or less, in some instances where made necessary by the design of the structure, and even then I used 1/2 or 7/16 sheathing.
That one you did sounds like it should be there for a while!
And yes, the best panels in the world are worthless if they are not fastened correctly, this means proper fasteners and proper spacing.
IIRC, the IRC accepts 3/8 panels for shear on bearing walls....but maybe I should look that one up.The heck, you say?
Plywood for shear on the inside of a garage or crawl space is a standard way to retrofit older structures that don't have sheathing under the stucco. Here in LA, they use 1/2" Struct #1. Nailing schedules are really extreme, like 2 or 3 inches on the edges, 4 - 6 in the field.
For a Rolls-Royce job, run glue on the framing first. BTW, there's a discussion of power and pneumatic caulk/glue guns in the Tools section. This is the kind of job that might justify that investment.
-- J.S.
Speaking of "educating the moron" -- what's a shear wall, and why would you need to do the interior of the garage with this stuff?
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"It is what we learn after we think we know it all, that counts."
John Wooden 1910-
A shear wall is a structure that is built to withstand forces in shear, like side to side and up and down the axis of the structure - in this case a wall. By taking a load bearing wall made of 2x4 or 2x6, and adding a surface of plywood or OSB, you create a wall that can not only support a load in the vertical plane, but can also hold it if it gets forces pushed on it from the side... as in wind or seismic forces. By covering all 4 sides of a structure, you create a solid box capable of withstanding ALOT of oddball forces. Shearwalls are one way of doing this, you can also do it with a let in 1x6 running diagonaly. Simpson makes a steel one you can cut in with a single saw cut then nail on the outside.
Here in SoCal, it is (or was in 1960) very common to crossbrace with a let in 1x6 on 2x4 stud walls, cover with wire and building paper, then wire mesh and stucco on the outside. The stucco is about 3/4" thick at its thinnest.
While everyone else normally has the shear wall on the outside, I'm putting mine on the inside. The stucco on the outside of the garage is perfectly fine, and I have nothing but bare studs on the inside. It boggles the imagination for some here, I know. I'm using 3/4" because I want to be able to hang just about anything I want - ANYWHERE - on my garage wall. Plus, it acts to hold the new 11.5" of height I added to the top of the old wall using two 2x12 boards. All approved by the building department, including the use of screws of course! (I suspect the first poster may be using a new account if he remembers that bit of information).Rebuilding my home in Cypress, CA
Also a CRX fanatic!
Depending on the seismic catagory, 2003 IRC still allows 1x4 let-in bracing. It's allowed for catagory C-1 story. Above thatv you have to apply something to the face of the studs. 5/16" plywood for 16" studs is allowed for all catagories. Paragraph R602.10.3
That 3/4 ply will sure make it easy to hang stuff on the walls.
"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
Edited 11/4/2005 7:54 am ET by FastEddie
Thanks for the education.FYI, I did drywall in my shop, and then pretty much covered the walls with 2' X 4' panels of birch ply, nicely finished and varnished. Like you, I wanted to be able to hang tools everywhere.Everybody thought it was a foolish extravagance; it still functions perfectly (I've reconfigured the shop about 3 times), and after 20 years it still looks great and is a very comfortable space. So have at it.........********************************************************
"It is what we learn after we think we know it all, that counts."
John Wooden 1910-
Why 2'x4' panels instead of 4'x8'?
"I suspect the first poster may be using a new account if he remembers that bit of information)."
Yes, that was too much of a coincidence. Good nose, PaulCP. http://www.costofwar.com/
Regarding your description of adding 2x12's to the top of the walls, that will create a wall that is weak in resistance to forces that are perpendicular to the face of the wall (like anything really heavy that is hanging off one side). Plywood up the side (one side anyway) will be helpful, but I'm surprised that passed the building dept. How did you extend the stucco on the outside?
Of course shear walls resist forces that act parallel to their face so the added height won't necessarily be a problem for that situation as long as the load can get into the shearwalls. I'm just wondering if the walls will tend to be flexible in and out of plane. If they are particularly long and straight (like a garage wall 20 to 24 feet long) they could be vulnerable unless they have some walls framed into them perpendicular.
Know what I mean about the 2x12's stacked on top? Didn't the building dept say anything about that?
Comments about anchoring the corners down are right on.
Here is the side view of my wall detail:
View Image
As you can see I'm not extending the stucco on the outside. Instead, I'm using cement board and extending the board and batten motif around the garage in this area. LTP4 shear plates and the cement board provide shear connection on the outside of the wall. The 1/2" rod, in combination with the plywood, keeps the built up header firmly a part of the top plate.Rebuilding my home in Cypress, CA
Also a CRX fanatic!
Paul, I agree with Junkhound that the hardwood ply will work fine for your shearwall. If the building dept okays it, you are golden. They may deny it because it is not approved/stamped/certified/whatever. Using the BC ply won't cost that much more, and you will be covered legally.I can imagine an AHJ not wanting hardwood ply as a shear panel because the glue is not waterproof. In you situation, that means the garage has to be flooded awhile before the big quake shakes it apart. Unlikely to happen, and we'll all have bigger issues to deal with if it does!Another poster suggested using glue on the studs to bond the shear panels. This is a bad idea. Nailed (screwed?) connections can flex some during loadings, releasing lots of energy safely. With the glue, nothing budges and the forces can crecendo until something major fails dramatically. I was bummed when I learned this, since I am a big glue acolyte myself.What you are doing is great, IMO. And I enjoyed the screw experiments you posted, too.Bill
I enjoyed the screw experiments you posted, too.
Hey thanks! I really appreciate that! I've got some new ideas percolating, so expect to see another SvN post in the future... hey, those old arrow wounds are almost healed ;)
Right now the walls are going up unglued - but not because I didn't want to do it. I will be running alot of new electrics around the garage, but I want some flexibility before I set them into my walls. I will be tacking them to the outside until I am cozy with their capacity and placement, then I will re-run the conduit and cut the holes for the boxes behind/inside the plywood. I was planning on glueing it then, but I see there is new information on that count as well to ponder! Maybe a looser flexible adhesive instead of a dry hard kind - we'll see when I get around to it.Rebuilding my home in Cypress, CA
Also a CRX fanatic!
> Another poster suggested using glue on the studs to bond the shear panels. This is a bad idea. Nailed (screwed?) connections can flex some during loadings, releasing lots of energy safely. With the glue, nothing budges and the forces can crecendo until something major fails dramatically. I was bummed when I learned this, since I am a big glue acolyte myself.
I find this difficult to believe. Nailed connections don't "flex". What happens is that the nails pull out of the wood. The connection isn't flexing, it's failing. A glued structure can be loaded until it fails, and it might well fail suddenly. But that will be long long after the non-glued version was just a pile of sticks.
-- J.S.
"Nailed connections don't "flex". What happens is that the nails pull out of the wood. The connection isn't flexing, it's failing." You are right, John, the connection is failing. However, the process can go on for quite awhile, and the bending, pulling out, enlarging of fastener holes in the sheathing, all allow for the dissipation of stress in a gradual manner, sort of like the crumple zones on a modern car do during a collision. The idea is that the shearwall can partially fail without endangering the occupants.On an unrelated note, thanks for posting a link to the clearvue cyclone site. From there, I went to Bill Pentz's site, which was a fascinating find, hours of good reading there.Bill
If this shear walling scheme was approved by your building dept plan checker isn't your question already answered? Or couldn't your just call them and ask? Or call your inspector and ask.
I took a weekend long course in earthquake retrofitting taught by a structural engineer and I learned a lot from it. I was just about the only non-pro in the class. He actually taught us how to calculate the amount of foundation bolts, the amount of sheer walling needed, the placement of the hold-downs, and the amount and placement of the hurricane clips. One of the things I learned that I never see anyone do is install hold downs at both ends of each shearwall. A shearwall without holddowns will just bounce your house off the foundation. He also was pretty darn adamant about not 'freestyle improving' the strength of the shear walls. Use the 1/2 ply with the correct 8d nailing pattern (from memory that was every 4" along the perimeter and every 8" in the field) because the engineers know exactly how strong that is and exactly how they will react in a shaker, you wily-nilly improve things and that goes right out the window. Did your building dept spec the hurricane clips from the shearwall to the floor joists? If not they should of.
I learned from the class that most building dept way overspec the amount of foundation bolts, they never spec the absolutely needed hold-downs, and never require the hurricane clips either. What you get is a half-arsed job that will do less than you think and can end up being more dangerous than not doing anything. I also learned that a ton of the pro earthquake retro-fitting contractors in the area were not doing the work correctly and were basically scamming the folks. This info mostly applies to the SF bay area where this engineer works and has been used as an expert witness in many a court case..... I have also seen this with my own eyes on many of the houses in my area that were 'earthquake retrofitted' by 'pros' or well meaning home owners who though that more has to be better.
Daniel Neuman
Oakland CA
Crazy Home Owner
> .... a weekend long course in earthquake retrofitting taught by a structural engineer ....
Any way to get that info in written form? Do they sell anything, or have classes in LA?
-- J.S.
The course is taught at the Berkeley building education center. The guy/class is local to SF bay area so I think that you are probably SOL for getting the info down south. The course does include a handbook that has most of the info covered in it but without the instructor there to explain everything I don't know how much good it would be. I do have an extra copy of the booklet but I don't know how okay it would be for me to give away the guys class material....um PM me or something.
I want to make something clear, the course is not a become a competent structural engineer in a weekend. What he teaches is a recipe that will work for like %90 of standard retro-fit situations. Its sort of interesting that he can do this in this day and age of sue happy folks....Daniel Neuman
Oakland CA
Crazy Home Owner
I take it you are referencing Howard Cook's class (Bay Area Retrofit).
He's quite upfront that he's not an engineer, but he's done a lot of thinking about how to build shear walls...
NotaClue
I take it you are referencing Howard Cook's class (Bay Area Retrofit).He's quite upfront that he's not an engineer, but he's done a lot of thinking about how to build shear walls...
Nope the instructor's name was Tony and we was a real structural engineer with a practice in SF CA.
Daniel Neuman
Oakland CA
Crazy Home Owner
Does Tony have a web site? Perhaps an e-mail address? Could you invite him to join us here on Breaktime?
-- J.S.
Does Tony have a web site? Perhaps an e-mail address? Could you invite him to join us here on Breaktime?
Nope no website. I'll email him and see if he's up to it. Though he does make his money as a consulting engineer so besides the class he teaches I don't know how excited he's going to be to be giving away his knowledge.
Daniel Neuman
Oakland CA
Crazy Home Owner
I appreciate your input on "half assed" upgrades. I'll look more into it based on the introduction you just provided.
My question was not about my shear wall design (it was approved by the local building dept, BTW), but about the specific plywood that can be used: Specificly, can cabinet grade hardwood faced 3/4" plywood be used as the sheathing on an internal (no weather exposure) shear wall?
I think I'll have to make a call to my building department again just to be sure about this specific material.Rebuilding my home in Cypress, CA
Also a CRX fanatic!
I appreciate your input on "half assed" upgrades. I'll look more into it based on the introduction you just provided.
My question was not about my shear wall design (it was approved by the local building dept, BTW), but about the specific plywood that can be used: Specifically, can cabinet grade hardwood faced 3/4" plywood be used as the sheathing on an internal (no weather exposure) shear wall?
Now that I think about it I'm pretty sure that your local BD is not going to okay any plywood that is not grade stamped. I looked thru the coursebook and the instructor recommends 1/2" Structural 2 CDX plywood.
You BD did okay your plans but that does not mean that your plans are good. Around here all the BD's have a set 'plan' they follow for earthquake retro fitting. I have learned that the plan over emphasizes some things (anchor bolts) while omitting other things (hold downs). If your plan does not involve hold downs and hurricane clips then I doubt it will be as effective as you hope.
As someone else mentioned the shear walls are supposed to flex a bit to absorb energy safely. It is possible to build your soft story so strong that it stays up and the living level of your house comes down around it (with you in it).
Daniel Neuman
Oakland CA
Crazy Home Owner
Ah, you crazy NorCal's... always with the hold downs! ;)
Every connection that I put in has either an H1, an A35, an HU26, multiple LPT4, or custom bent 16ga. strap (with far more than 10 fasteners per side). The head of the BD asked me if I owned stock in Simpson.
Out of curiosity, could you explain to me how a hold down offers superior protection over a standard anchor bolt with a shearwall? I know the hold down is obviously stronger and better at connecting with the vertical studs, but a shear wall is also well connected to the horizontal plate and to the vertical studs. How exactly does it prove its worth? When I try to visualize it seems like a wash.
No worries about the soft story... there is only one story on this house at the moment that I'm dealing with, and it's on a slab.Rebuilding my home in Cypress, CA
Also a CRX fanatic!
With a shearwall, the vertical load is concentrated at the ends of the wall or panel. (the shear force between the plywood and the end stud is vertical) Keep in mind that it is easier to lift up (or hold down) the corner of the wall panel than to lift or hold the whole thing. The shear force between the plywood and the bottom plate is horizontal. A typical hold down anchor that one should be referring to when discussing shear walls is something like Simpson products: PA, PHD, HHDQ or similar. These fasten directly to the studs and deal with the vertical component of the shear wall more directly (as you said).
I think the direct link of the stud to the anchor bolt, thru the HD anchor is greatly superior to the linkage of the common studs to the plywood, to the bottom plate, to the anchor bolt. The concentration of nails right where the forces are transferred seems like it has to be a lot better. There just aren't enough nails close to the anchor bolt to transfer the vertical components of the load from the bottom plate into the AB, not to mention the size of the washer would not normally be as large with the common AB compared to the contact area of the HD anchor. Additionally, by placing them (HD's ) at the corners, they are located in the most advantageous spot.
With a shearwall, the vertical load is concentrated at the ends of the wall or panel. (the shear force between the plywood and the end stud is vertical) Keep in mind that it is easier to lift up (or hold down) the corner of the wall panel than to lift or hold the whole thing. The shear force between the plywood and the bottom plate is horizontal. A typical hold down anchor that one should be referring to when discussing shear walls is something like Simpson products: PA, PHD, HHDQ or similar. These fasten directly to the studs and deal with the vertical component of the shear wall more directly (as you said).
Yea what he said.
The vertical forces on the shear panel are going to be greatest at the outside edges of the panel. The course instructor recommended the PHD-8 from Simpson I believe. Whoa man the course was like 2 years ago. But I believe you install the hold down in tension and use thru bolts to attach it to the stud.
Daniel Neuman
Oakland CA
Crazy Home Owner
Personally I would be concerned about the HD hardwood plywood. In addition to the lack of stamps, there is a reason it is cheaper - 'cause it really is. At least the stuff I've used from there before. Big voids, the minimum number of plys - (kinda) pretty on the outside but ugly on the inside - reminds me of some people I know :-). Not sure about the ply material either in terms of strength. I'd stick with the graded & stamped stuff; AC or BC.
Yep, I know exactly what you mean. They have a 1/2" 3 ply that is cheaper then their 1/2" 4 ply - I would not us that crud for anything other than the gap filler I used it for.
The stuff I'm talking about here though looked really good, no visable voids and lots of thin plys, seven layers if my memory serves, rather than the standard five on AC/BCRebuilding my home in Cypress, CA
Also a CRX fanatic!