Plywood-Putting up

Hrose77

When your putting up exterior plywood is there a technique to put it up? Do you put it horizontally, vertically, leave a space at the bottom or but it up avaunt the concrete, what type of screws/nails?

jklingel

Plywood is typically installed vertically. Wood against concrete is generally pressure treated, and requires stainless or hot dipped galvanized nails (there was recent discussion about this here, and I am very concerned about this treated wood now; it seems to eat everything. Perhaps TimberSil is the answer.) I believe 10D nails are usually recommended for 1/2" or 5/8" plywood, about 6" OC at the edges and 12" OC in the field. You can screw it, too, but that is very time consuming.

chrisBC

Proper practice is actually to put the sheets horizontally-this is stronger and is simply the right way to do it. If you have a thinner rip, this always goes in the middle-not at the top or bottom of a wall. It is also always good practice to never have a joint at a door or window return, always return it over the door/window by a foot or two. Just like drywall. Good strong building methods. Also-just like drywall or brickwork-always stagger your plywood joints, by at least one stud space.

I always put a quarter inch or so gap-about the width of a carpenters pencil-in between sheets. I wouldn't put them tightly together. You need plywood that is meant for sheathing, most of the time standard construction plywood is fine, tell them at the lumber yard what your needs are they will tell you what to buy. I am assuming by "exterior plywood" you mean the sheathing that covers your framing, that will be covered by housewrap and siding.


Use hot dipped galvanized, 6 inches around the perimeter of the sheet, 12 inches in the field.

Most codes will dictate using nails-not screws-for sheathing. I wouldn't use screws. I am assuming you are using 3/8's or half inch for this, as most wall sheathing is this size. Five eight or 3 quarter inch is generally used for subflooring/decks.

If you are confused about technique to install it, go look at any house being build, look at how they do their plywood. (some are better than others however)

kwikfishron

You can actually run it either way but keep in mind that you need maintain “full perimeter nailing” , so if you run it horizontally you’ll need blocking at 4’ for nailing making vertical installation preferable.

Check with your building department for size of nails and spacing. I’ve worked in areas that required 3” perimeter nailing. 8d nails with 8” perimeter and 12” field nailing is pretty common though.

You don’t want the plywood touching the concrete.

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DangerMouse

True, but ONLY when the PT lumber is the correct type made for GROUND CONTACT! There IS a difference and an inspector would likely make you remove it and use the correct type. When I did this home, I used the correct type for the first 2' at the bottom, then normal ply for the rest. (I believe minimum required is 6")

DM

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jklingel

Danger: Never heard of different types of PT wood. How do you tell the difference, and what is the ground contact stuff called? thanks. j

DangerMouse

GC is twice as heavy to begin with, it's practically drenched in the chemicals! It's like working with green hardwood!
I don't know the chemistry, only that it may make a BIG difference to an inspector and then your wallet! (Oh yeah, it costs more too, of course)

DM

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kwikfishron

By number on the little tag stapled to the board.

Third question down the page.
http://www.strongtie.com/productuse/ptwoodfaqs.html

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AaronSharp

vertically always

jklingel

Thanks, Ron. The more I read about PTW, the better TimberSil looks.

Tizzer

Never heard of 1/4" gaps or hot dipped galvanized nails for sheathing - unless it will be sitting out in the weather for months on end.

Clutchcargo

Nope. horizontally is correct for strength. OSB on the other hand, doesn't matter. leave a gap between sheets the size of a 16d nail.

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Gary in WA

Wow, so many different answers.....

Minimum code; http://bct.nrc.umass.edu/index.php/p...n-the-outside/

http://publicecodes.citation.com/ico...002_par025.htm

“The racking resistance of APA plywood or OSB wall bracing panels and the lateral load capacity of a shear wall for wind and seismic loading are not affected by the orientation of the sheathing panels. Panels may be installed with the long, or strength, axis either horizontal or vertical. All panel edges of shear wall sheathing, however, must be attached to framing or blocked. Although not required by model building codes, some local jurisdictions require blocking of horizontal panel joints at wall bracing segments (generally building corners and at 25 foot intervals in long walls). For this reason many designers and builders prefer to install sheathing with the long axis vertical, thus avoiding the need for additional blocking.”---- http://www.apawood.org/pablog/index....al-or-Vertical


Jk, the little plastic tags are on lumber, there is an ink stamp code on the plywood back-side for the different exposures: one for exterior use- UC3B, three for ground contact or fresh water- UC4A, B, C, three for under salt water depending on location: Enter: Q220 here: http://www.apawood.org/level_c.cfm?c...ub_ply_libmain


Gary

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Clutchcargo

I asked this same question about two years ago. The answer I got was that plywood installed horizontally and unblocked has the same shear strength as if installed vertically. If you add blocking to a horizontally installed panel, the shear strength is 40% greater.

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Hrose77

What is "blocking" that people are referring to?