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Exterior sheathing; proper application

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May 11, 2013, 04:38 PM
Exterior sheathing; proper application

I've mentioned in other topics that I want to replace much of the exterior sheathing.
Many of my home's walls are 8 1/2 to 9 feet tall, so how do I best make use of the 4' x 8' plywood sheathing panels? I asked at one of the big box stores about the availability of 4' x 9' sheets, but was told I'd need to order a huge amount.
One thing I've considered (something I've seen a couple of contractors do on YouTube) is to use pressure treated plywood for the bottom 1 to 1 1/2 feet, then use untreated plywood for everything above. Is that a good use of material?
What should I do at the seams (I saw one guy caulk his seams)?
What is better; vertical or horizontal application? As an example, if I have an 8' x 8' area to cover, would it be better to mount the sheets horizontally? Structurally, it would seem stronger than if I mounted them vertically, but, with horizontal application, I have more "open" seams (i.e., they don't fall on studs).
Also, at the bottom, where the sill plate sits on top of the block or concrete, should the sheathing overhang the block at all?

Thanks in advance.
May 11, 2013, 05:29 PM
(1)Is this exterior sheathing that is the final product, like T1-11?


(2)Is it exterior sheathing that is covered b some form of siding?

If #1, then a couple of solutions: Go to a regular lumber yard (not a big box store). They will either stock the longer sheets or can order exactly the quantity that you need. Probably can get it in within a day or two.

If you stay with 8' material, there is a shallow 'Z' flashing that is made to go between the two pieces. This way both pieces are installed on the same plane yet water cannot leak past the seam.

If it's option #2, then you really don't need to do anything although the 'Z' flashing would not hurt. Better though to use Tyvek on top of the sheathing to cover all the seams. No real reason to use PT material unless your framing is only a few inches off the ground.

On the bottom overhang, I prefer to make the outside surface of the sheathing flush with the block (assuming this is situation #2 above). Then your siding can overlap the foundation by a little without exposing the plywood edge of the sheathing.

If it's situation #1 above, then the outside of the framing should be flush with the outside of the foundation so that the T1-11 will overlap the foundation

This message has been edited. Last edited by: Jaybee,

May 11, 2013, 10:32 PM
Thanks Jaybee,

It's situation #2, exterior sheathing that will (hopefully) be covered by Hardie Shingles (I say, hopefully, because I'm no longer sure I can afford the Hardie).
The level of the sill plate is pretty close to grade. In fact, in a few areas I had to do some re-grading by hand just so the dirt wasn't touching the existing cedar shingles.
I plan to use Azek as a banding board so the siding will be more than six inches above grade.
Good idea regarding the 'Z' flashing.

Thanks again.
May 12, 2013, 12:10 AM
Since Hardi recommends installation on top of Tyvek, I'd go with that. Then no Z flashing or caulking is needed at any of the sheathing seams.

May 12, 2013, 02:49 PM
Is ZIP sheathing available and a pricing option in your area? Just tape the seams, never again working with Tyvek, as not matter what day you work with it you notice the wind.... Just another option to think about. Good luck...

Popeye only reached for the Spinach can as a last resort...
May 12, 2013, 09:08 PM
Thanks CommonwealthSparky and Jaybee.

ZIP sheathing is an interesting idea. It does look like it would simplify things quite a bit. It seems like you pay dearly for that convenience though. I just looked it up. Lowes has 1/2" x 4' x 8' Zip system for $32.04. 7/16" x 4' x 8' OSB is $12.57. Also, I don't want to start a religious war over OSB vs. plywood, but I'm thinking that plywood would hold the nails better to hold the Hardie on.

I recently viewed a Matt Risinger video on YouTube where he recommended using Tyvek Commericialwrap D. Apparently, it's more heavy-duty than "regular" Tyvek and less prone to tearing. I have no idea how much more expensive that would be, because it's not carried by the "big box" stores.