DIY Home Improvement Forum banner
1 - 20 of 21 Posts

·
Registered
Joined
·
25 Posts
Discussion Starter · #1 ·
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?
 

·
Registered
Joined
·
1,943 Posts
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.
 

·
Registered
Joined
·
500 Posts
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)
 

·
Super Moderator
Joined
·
12,638 Posts
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.
 

·
the Musigician
Joined
·
10,404 Posts
Wood against concrete is generally pressure treated
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
 

·
Registered
Joined
·
1,943 Posts
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
 

·
the Musigician
Joined
·
10,404 Posts
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
 

·
Registered
Joined
·
511 Posts
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.
 

·
Registered User
Joined
·
11,730 Posts
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?content=pub_ply_libmain


Gary
 
  • Like
Reactions: DangerMouse

·
I have gas!
Joined
·
2,418 Posts
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.
 

·
Super Moderator
Joined
·
12,638 Posts
What is "blocking" that people are referring to?
Anywhere I’ve ever worked the wall sheathing must have full perimeter nailing.

If you run the sheets vertically this is achieved by the studs and the top and bottom plates.

If you run the sheets horizontally the top edge of the first row of sheets will only have the studs to nail to. You need to add a row of blocking between the studs for nailing.

The blocks not only for nailing but also a fire stop.

If the sheathing is installed as mentioned (horizontally with no blocks and a gap between the sheets) this would be inviting fire to enter the wall cavity.

Look around at new construction I doubt you will see many if any with horizontal sheathing. Any strength it may add is outweighed by the extra material and labor cost to the framer.

Plumbers and electricians don’t think much of it either.
 

·
KemoSabe
Joined
·
644 Posts
Anywhere I’ve ever worked the wall sheathing must have full perimeter nailing.

If you run the sheets vertically this is achieved by the studs and the top and bottom plates.

If you run the sheets horizontally the top edge of the first row of sheets will only have the studs to nail to. You need to add a row of blocking between the studs for nailing.

The blocks not only for nailing but also a fire stop.

If the sheathing is installed as mentioned (horizontally with no blocks and a gap between the sheets) this would be inviting fire to enter the wall cavity.

Look around at new construction I doubt you will see many if any with horizontal sheathing. Any strength it may add is outweighed by the extra material and labor cost to the framer.

Plumbers and electricians don’t think much of it either.
It's a regional thing. I framed along the East Coast of NJ for 20 years. Never was blocking required for perimeter nailing on exterior sheathing and it was installed horizontally 99% of the time.

We always space our seams and edges. Many of the buildings are less than 10' apart in some communities.

4' setbacks required fire rated sheathing panels, 5' did not, however all bearing walls were required to have 5/8 Type X drywall on the interior.
 

·
Registered User
Joined
·
11,730 Posts
Not the distance, as loneframer said: http://publicecodes.citation.com/icod/irc/2009/icod_irc_2009_3_sec002.htm

I don’t think the blocks were for fire-stop, only at ceiling/floor and every 10’ horizontally: http://publicecodes.citation.com/icod/irc/2009/icod_irc_2009_3_sec002_par031.htm

Blocking is for shear walls as I quoted above, depends on your location for the seismic/wind design: http://publicecodes.citation.com/icod/irc/2009/icod_irc_2009_3_sec001_par004.htm

The shear values are way different depending on orientation without blocks: http://www.trioforest.com/pdf/Load-Span_Tables.pdf:, Table 1: The blocks even it out, though I have no idea how much.....


Example: http://www.awc.org/pdf/WFCM_90-B-Guide.pdf

Gary
 
1 - 20 of 21 Posts
Top