Wavy Barn - 1/4" ply enough?

17sq, 8/12 pitch, 1800s post & beam construction, rafters at 28", 1x12 sheathing. Barn is uninsulated.

Will rip off the old and just want to make sure I put up enough for the nails to hold the Landmarks. The roof has character (waves). I have put up 1/2" with 2" ring shanks on lower pitch several times before.

Is the 1/4" enough, or should I wrestle with the 1/2" up there. Maybe 3/8"?

Anyone know of any code issues in Massachusetts on this subject?

Thank you very much for your help.


Are you sheathing over the 1x12 planks?

1/4 will not hold a nail for any reason.

I don’t know about code in your area but I would think that it would be best using minimum of 3\8".
The problem with using 1\4" over spaced sheathing is that some courses are likely to have only the 1\4" sheathing to nail into (between the gaps in the 1" x 12"'s).
If the 1" x 12"'s are all solid the sheeting isn’t really a structural part of the building (the sheeting), but you still need the minimum 3\8" in the gaps to hold the nail good.
Framing nailers tend to sink nails too far into 1\4" also.
If the 1" x 12"'s are butted tight to each other you won’t have the issue of gaps and all the nails should hit decking of adequate thickness.

Yes, I would be going over the existing 1x12s (true dimensions), they seem to be OK, just two places where they will probably need repairs, and one side as been subjected to a thin roof for one year with some leakage.
Also I’ll be doing Grace I&WS over entire roof.

Thanks. No they are not butted tight. Sounds like 3/8 may be choice.

Are there spaces between the 1" x 12"'s?

Either way IMO you should use 3\8" minimum.


Why do you want to use Storm Guard? Exspecialy over the entire roof?


Yeah, customer wants it. People start seeing houses around here getting completely covered and start requesting it.

No felt, just I&WS. I know that it is often done in Alaska.

I will still be talking to him about the need for proper ventilation.

I don’t know about Beantown (or it’s surrounding areas…) but here in Texas, 1/4" costs more than 1/2" (type) OSB (actually 15/32" or 7/16"). Even SolarBond or ReflecTech CDX costs less than 1/4".

IIRC, 1/4" is typically Luan & therefore a ‘true’ plywood, although not a high end ply.

Will this structure be fully visible to the underside of the decking or is it going to be a converted barn into a living space? Are you venting the roof - intake & exhaust?

3/8" plywood is Massachusetts code for a minimum. We do a lot of old buildings “1600 & 1700s” and cover the old decking with 3/8 quite a bit.

3/8" is minimum code here as well, but I’d never put it on anything (maybe if I got a lot of it for free I’d use it for walls, but that’s about it).

That is too thin IMO & will suffer dips & heaves after about 20 years, especially if you’ve got a heavier dimensional vs. a lighter 3 tab.

I have done plenty of that roof & they really do feel squishy to walk on after 2 decades. Yes, I know we don’t deck a roof for walking, we deck 'em to shingle… but walking a roof will give you an indicator (one of many) as to how a roof is performing.

Thanks RHR (I went to UT Austin, Go Horns)

I was all set to use 3/8, but maybe I should resign myself to 1/2 up there.

These 27" rafters aren’t consistently OC. I don’t plan on ending the 4x8s on rafters, just nail it down good on the ends along with all the roofing nails. I have used 2" galv rink shanks previously on a 12" grid on houses. Any suggestions on fasteners?

Still concerned with how it will all lay down.

3/8" is only good if you are resheathing over the old decking, in that case it makes a strong deck for a fair price. If you have to remove the old sheathing then you should use a min of 5/8" exterior grade CDX plywood “never OSB”.

It would be a good idea to make sure that the seams on the sheeting line up with rafters…
If you don’t it is possible\likely that the seams that aren’t nailed into rafters will “pop”.
1" thick material isn’t strong enough to hold the 8d or better nails you are going to use to hold down the sheeting, especially when it is old 1" material.


Here we go again with the OSB haters.

Lots & lots & lots of Multi gazillion dollar houses go up with OSB all the time. Never any problems. I’ll bet Bill Gates’ house has OSB. Don’t get it wet & you’re fine.

Make sure you’re laying the decking (any decking) horizontal so it’s 4’ up & 8’ sideways… stagger the decking in a sort of “brick” pattern; do NOT line up all the edges in one vertical line.

You never mentioned if it’s a visible interior to the underside of the decking & rafters; if appearance isn’t an issue, then I’d suggest adding new 2x’s (4, 6, 8’s depending on the existing system) to the sides of the rafters provided your framing system will hold the added weight. That will get you a better support system for your decking.

PS: Baylor this weekend, in Wacko. Should be a fun “almost home” game. You should spend some time with us on HornFans.com. Look on this page under the tab that says “Roofing Business” & click the “get on my level” thread. :wink:

yeah, i agree why are some of you guys so against OSB. to prove a point i put 1/2 sheet OSB in the back of my truck in april. put 1/2 sheest of 1/2" cdx in my brothers truck at same time. his was delaminated and warped in a week. mine is still there and looks almost new. so why the hating?

uh, I have no problem with osb…

It was just part of the quote.

Now that you mention it, I do work for a builder who is probably THE best in my area, they do not use osb because they build “health Houses”.
I am told that osb gives off voc’s over time that can be irritating to “sensitive” people…

Which then brings us to issues of proper attic venting.

Actually I love OSB. I love it when we have to rip it off a 20 year old house and redeck the entire house with exterior plywood its a great upcharge. Almost no builders use it for roof sheathing anymore although some will use it for the walls to save a buck, Its all about saving money with some.

News Flash:

Yuh huh they do. Lots. Large scale developers as well as custom home builders.

I have yet to do any new construction on a house that’s ‘true’ ply.