1/2" vs 3/8" Plywood Sheathing

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Jul 24th, 2021 12:01 am

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Jul 22nd, 2021 12:40 pm

Jagstyles [OP]: Deal Addict; Aug 7, 2013; 1623 posts; 523 upvotes; GTA

Jul 22nd, 2021 12:40 pm

1/2" vs 3/8" Plywood Sheathing

We are redoing our roof and it requires all new sheathing due to significant moisture issues and rotting OSB boards from the previous owner. Each quote we've received has given us the OSB option or 3/8" plywood. My understanding is that before the recent price surge in lumber, the standard for plywood sheathing was 1/2".

Prices have come down but still haven't really been reflective with suppliers since they are working through their old supply still. We have to have this done and wondering would it be sufficient to use 3/8" plywood sheathing or pay the extra and go with 1/2"? Using all Landmark products as well.

Thanks

21 replies

Jul 22nd, 2021 2:42 pm

dbracer: Member; Aug 25, 2006; 250 posts; 238 upvotes; Toronto

Jul 22nd, 2021 2:42 pm

depends on of rafter spacing

24" spacing requires 1/2" osb or ply

16" spacing requires 3/8" osb or ply

These are *minimums*

If you have a more flat roof pitch I'd personally spring for 5/8" to be honest.

Check building code for your area.

+3

Jul 22nd, 2021 3:15 pm

torontotim: Deal Addict; Nov 17, 2012; 4951 posts; 4506 upvotes; Toronto

Jul 22nd, 2021 3:15 pm

What's the difference in price? I'd 100% go for 1/2" plywood and would ask about 5/8" as well.

This should be a once-in-a-lifetime investment, and if/when you do sell the house an inspection will reveal at least plywood vs. OSB. A mature home buyer would be keen to know what the sheathing is.

Worth the investment in my opinion.

Take loads of photos during the job. If you could set up a camera at a neighbor's place I'd do time-lapse photos with a GoPro or something if you can. You can't keep an eye on the job all the time, and you'll want photographic evidence of what they actually did once the shingles are on and you can't see it anymore.

Jul 22nd, 2021 3:18 pm

Benzat17: Sr. Member; Dec 26, 2017; 853 posts; 681 upvotes

Jul 22nd, 2021 3:18 pm

i just replaced my shingles

plywood were in good condition except couple i had to replace

24"spacing
3/8" ply
roof slope 4/12

i had to walk on the rafters as if i step in the middle between two rafters i would break it or hear it break. my friend was able to walk no problem as he was half my size at 120lbs

i wish price of wood were cheaper i would have replaced all of them with something thicker than 3/8 but i figured i wont go up there for another 15 years so its okay

+1

Jul 22nd, 2021 3:50 pm

lamin: Deal Addict; Jan 21, 2011; 1287 posts; 684 upvotes; GTA

Jul 22nd, 2021 3:50 pm

If you plan to stay there for a while, use ply.

Jul 22nd, 2021 7:08 pm

jacquesstrap: Deal Addict; Nov 9, 2008; 1852 posts; 877 upvotes; Toronto

Jul 22nd, 2021 7:08 pm

I would want 1/2" ply at MINIMUM. I would never use OSB for my roof, or in any part of my home to be quite honest. I built a shed several years ago and used 1/2" ply for wall and roof sheathing - wouldn't use OSB there either.

Call me a snob but I'd rather build something right the first time and have it last, than cheap out on the structure of a building to save a few bucks.

+1

Jul 22nd, 2021 8:35 pm

Toukolou: Deal Fanatic; Dec 4, 2009; 8304 posts; 4212 upvotes

Jul 22nd, 2021 8:35 pm

I doubt very much you could/would get a monetary return on this outlay for resale, but, for peace of mind I'd likely spring for the 1/2" if I was planning on staying a long time.

That being said, if the roof is shingled and vented properly, even OSB will last a long, long time.

"I'm a bit upset. I've been grab by the back without any alert and lubrification"
Lucky

+1

Jul 23rd, 2021 12:31 am

Benzat17: Sr. Member; Dec 26, 2017; 853 posts; 681 upvotes

Jul 23rd, 2021 12:31 am

Other than thickness why would you go with 1/2" ? It's not like you walk on the roof everyday
Or am I missing something?

I know plywood interms of not absorbing water is much better than OSB but don't get the thickness

Jul 23rd, 2021 1:46 am

craftsman: Deal Expert; Jan 27, 2006; 21135 posts; 14657 upvotes; Vancouver, BC

Jul 23rd, 2021 1:46 am

Benzat17 wrote: ↑ Other than thickness why would you go with 1/2" ? It's not like you walk on the roof everyday
Or am I missing something?

I know plywood interms of not absorbing water is much better than OSB but don't get the thickness

Thickness is just a question of how much weight the material will support when new as well as 10 or 20 years from now. One of the most common misconceptions is that water only comes from above - ie the rain water/snow melt - but in many older homes or the ones that aren't sealed correctly, moisture often comes from below as well from warm moist air coming into a cold attic either via leaks (most common I would think in most homes regardless of age) and via poor construction practices like venting bathroom fans into attic spaces. You see the results from RFDers all of the time via pictures of mould growth in attics. In the first few years, it's not a problem but over several years, the material can weaken with constant exposure to that moist warm air condensing into water droplets. By going for that extra 1/8 of an inch, you just have that extra bit of safety especially a few years out from the initial installation.

Jul 23rd, 2021 8:57 am

projectman44: Sr. Member; Jun 1, 2017; 899 posts; 832 upvotes; Mississauga

Jul 23rd, 2021 8:57 am

I cant see why you would consider 1/2" unless you're installing a metal roof. Especially now that you have brand new sheathing.

I assume your roof is greater than a 2/12 pitch?

Jul 23rd, 2021 10:26 am

Jagstyles [OP]: Deal Addict; Aug 7, 2013; 1623 posts; 523 upvotes; GTA

Jul 23rd, 2021 10:26 am

projectman44 wrote: ↑ I cant see why you would consider 1/2" unless you're installing a metal roof. Especially now that you have brand new sheathing.

I assume your roof is greater than a 2/12 pitch?

Yes, roof is definitely greater than 2/12 pitch. The only area it's not is my covered porch where it's exactly 2/12 pitch and currently has OSB.

Jul 23rd, 2021 10:27 am

Jagstyles [OP]: Deal Addict; Aug 7, 2013; 1623 posts; 523 upvotes; GTA

Jul 23rd, 2021 10:27 am

lamin wrote: ↑ If you plan to stay there for a while, use ply.

Definitely using ply, just a matter of whether to go with 3/8" or 1/2".

Jul 23rd, 2021 10:27 am

Jagstyles [OP]: Deal Addict; Aug 7, 2013; 1623 posts; 523 upvotes; GTA

Jul 23rd, 2021 10:27 am

dbracer wrote: ↑ depends on of rafter spacing

24" spacing requires 1/2" osb or ply

16" spacing requires 3/8" osb or ply

How do I determine what the spacing is?

Jul 23rd, 2021 10:33 am

jacquesstrap: Deal Addict; Nov 9, 2008; 1852 posts; 877 upvotes; Toronto

Jul 23rd, 2021 10:33 am

Jagstyles wrote: ↑ How do I determine what the spacing is?

Easiest way is to look in your attic at your roof rafters

Jul 23rd, 2021 10:43 am

Jerico: Deal Guru; Jan 25, 2007; 12407 posts; 7583 upvotes; Paris

Jul 23rd, 2021 10:43 am

Benzat17 wrote: ↑ i just replaced my shingles

plywood were in good condition except couple i had to replace

24"spacing
3/8" ply
roof slope 4/12

i had to walk on the rafters as if i step in the middle between two rafters i would break it or hear it break. my friend was able to walk no problem as he was half my size at 120lbs

i wish price of wood were cheaper i would have replaced all of them with something thicker than 3/8 but i figured i wont go up there for another 15 years so its okay

2021-07-22_15-19-53.jpg

My first house was like this. Sure glad I didnt live more north where rooves need to be shoveled or get ice build ups.

Jul 23rd, 2021 1:44 pm

tempperm: Sr. Member; Mar 10, 2004; 848 posts; 329 upvotes

Jul 23rd, 2021 1:44 pm

Call it overkill but i did 3/4 recently. Like the heftiness. Painful to pay almost 100 dollars a sheet though. I would do it again.

Jul 23rd, 2021 1:53 pm

engineered: Deal Expert; Feb 11, 2007; 20274 posts; 24022 upvotes; GTA

Jul 23rd, 2021 1:53 pm

tempperm wrote: ↑ Call it overkill but i did 3/4 recently. Like the heftiness. Painful to pay almost 100 dollars a sheet though. I would do it again.

That's a lot of extra weight on the roof. Shouldn't an engineering assessment be done to be sure it's safe?

If the women don't find you handsome, they should at least find you handy.

Jul 23rd, 2021 3:28 pm

tempperm: Sr. Member; Mar 10, 2004; 848 posts; 329 upvotes

Jul 23rd, 2021 3:28 pm

engineered wrote: ↑ That's a lot of extra weight on the roof. Shouldn't an engineering assessment be done to be sure it's safe?

I just copied what was done previously. Didn t have issues then so i don t anticipate any issues now.

Jul 23rd, 2021 3:31 pm

engineered: Deal Expert; Feb 11, 2007; 20274 posts; 24022 upvotes; GTA

Jul 23rd, 2021 3:31 pm

tempperm wrote: ↑ I just copied what was done previously. Didn t have issues then so i don t anticipate any issues now.

If the house was originally engineered with 3/4 then that makes sense.

If the women don't find you handsome, they should at least find you handy.

Jul 23rd, 2021 11:18 pm

TrevorK: Deal Expert; Aug 2, 2001; 18280 posts; 9499 upvotes

Jul 23rd, 2021 11:18 pm

Take a look at your shingles manufacturers install guide. GAF for example says that 3/8" is acceptable:
Plywood or OSB… 3/8” (9 mm) minimum thickness, C-D Exposure 1 APA Rated, as recommended by the APA – The Engineered Wood Association

That said, I would go for 1/2" myself as a it is the minimum for a metal roof. Cost increase should be minimal, install is the same. 5/8" would be better but I know you have to stop somewhere.

If you're able to wait a bit it looks like prices are starting to slowly come down at the big box stores. This week was the first price drop I have seen at Home Depot for OSB, so perhaps they are starting to go down. If they are and they follow the same path as lumber even waiting a couple months is a big savings.

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