Building greener on a budget: can we safely use mixed-size plywood?
Hello Folks,
We’re taking on the challenge of building our first home and garage in the Northeast (climate zone 6a), and doing our best to keep costs low while still making sure the structures are solid and durable. My questions are about whether reclaimed, irregularly sized plywood can be safely used for sheathing and subflooring—especially when paired with advanced framing techniques like 24-inch on-center spacing.
There’s a factory nearby that makes plywood items and will sell us the remaining trimmed plywood sheets at a real discount. They’re straight and flat, but come in irregular sizes. All sheets are 4 feet long, but their widths vary from 32” to 36”. Bundles are available in 1/2″, 5/8″, or 3/4″ thicknesses.
We’ve reviewed expert sources on sheathing and subflooring, but haven’t found clear answers to the following questions:
1. Are there any serious concerns with using 5/8″-thick, variable-width (32″–36″) plywood as wall and roof sheathing on a single-story garage framed with 2×4 studs spaced 24” on center?
2. Are there any serious concerns with using 5/8″-thick, variable-width (32″–36″) plywood as wall and roof sheathing on a 2-story home framed with 2×6 studs spaced 24″ on center?
3. We’re using Advantech for the first floor. But for the second story, are there any serious concerns with using 3/4″-thick, variable-width plywood (32″–36″) as subflooring over joists spaced 24″ on center? We’ll be installing pine boards as the finished flooring on top.
Any guidance, experience, or red flags to be aware of would be greatly appreciated! Thanks in advance!
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Replies
First thoughts:
- I'd talk to a structural engineer about using 4' long plywood sheets of varying widths in any of the scenarios mentioned above.
- Are you self-performing the work? If so, and if using all smaller sheets of plywood works structurally, and if the discount on material is significant enough, and if you don't place a high value on your time, this could work. If you are not self-performing the work, any material savings is likely to be rapidly eclipsed by increased labor cost.
Even if they're doing the work, their time is limited. Once you start framing you want to get dried in as quickly as possible.
I know that every dollar counts, but this isn't where I'd pick to economize. In the scheme of a house the cost of the sheathing just isn't a big number.
Leah,
I second Paul's advice about talking to an engineer.
Practically see two possible problems:
- On roofs and walls you want to stagger the joints between sheets, which wouldn't be possible with variable widths.
- On floors that difficulty is compounded as you want to use t&g for the subfloor.
You have to meet wind-bracing requirements, which vary greatly with location: https://codes.iccsafe.org/content/IRC2021P1/chapter-6-wall-construction#IRC2021P1_Pt03_Ch06_SecR602.10.
Once you have done that, I can't think of anything in the IRC model building code that would prohibit what you propose. But for the reasons the others have listed, I would be wary.
If you use random pieces of "regular" (non T and G) plywood as subfloor, you have to put blocking under the seams between sheets. That will complicate the project a bit, but it's doable.
For walls, shear resistance is the big concern. You might be able to use random plywood more easily if you use diagonal let-in bracing on the walls.
I agree with the others about talking to an engineer prior to attempting this. It would be helpful for the engineer to have an idea of the sizes of plywood pieces you have, such as "I have a lot of 1/2" pieces in 2x4 foot panels, but some 15% or so are 3x5 foot", etc.
Bill