3/8" plywood roof sheathing

I’d never seen a home with anything less than 1/2" roof sheathing until the other day when I found one with 3/8" plywood. It had what I called “excessive deflection” but was probably 45 years old with no signs of failure.
Not desireable certainly, and the buyer was unhappy that I didn’t call out for a new roof, but with no visible failure, I couldn’t justify it.

If the roof sheathing has excessive deflection I would consider it failing under the circumstances, and will probably continue to fail.

This roof deck deflectived excessively starting the day it was installed 45 years ago. So if for 45 years it has protected the living space and supported structural loads without visible damage… it’s not a mechanical failure, it’s still intact.
Every roof deflects and as far as I know there are no tables of allowable deflection. I guess it’s a matter of engineering practices of 1960. Anyway, I told him I would defer to a structural engineer if he wanted to pursue condemning the roof.

I have to agree with you. 45 years is a long time for under sized roof sheathing to last. It must be a steep pitched roof. Are the rafters 16"oc and how is the snow load from those Colorado winters. I would certainly mention it but condemn it. Probably not. If it ain’t broke, don’t fix it.

About 3 or 4 & 12, 24" oc, roof has probably seen 40" of snow at some point and 80 MPH winds.

This was the worst of the damage I found, damage where someone stepped on the joint, but I’ve seen 1/2" plywood break the same way where there were voids in the laminations at the edge of the sheet. Maybe it’s not 45 years old, maybe it’s a re-roof, but if it is, it’s still an old one.

Just a bad choice by someone trying to save money. It’ll hold up as long as no moiture gets to it, but it won’t take much decay for someone’s foot to go through.

That’s texture overspray in the foreground (shot up through the access).


I might be wrong, but evidence in the picture seems to tell me that an H-clip was used that was meant for 1/2" material and that is why the sheathing is sagging.
45 years ago dates us back to 1961. Back in those years if I recall, plywood was not a popular commodity, at least not in Northern Maine. Something is wrong with this picture and I would have called it out as inadequate for support of the intended design and recommended evaluation by a Prominent Building Contractor.

Marcel :slight_smile: :slight_smile:

Although the roof appears to be functioning as intended at the time of inspection it appears to be near the end of it’s life expectancy, It is recommended that a licenced roofing contractor further inspect the roof and evaluated it’s overall condition and further recommendation is advised.

Hey Marcel;
Do you have licencing in ME? I may be looking for a job

Hey Peter;

No. Maine does not have HI’s Licensing.

Marcel :slight_smile: :slight_smile:

True…and they sure didn’t have H-Clips 40 years ago.

Good points about the H clips. I got into the trades (carpentry) in Colorado 1970 (plywood roofs here at that time), but I don’t remember installing H clips until about 1980 in California. Doesn’t mean they weren’t around before that, but I’ve only seen them installed in roofs and this is the only 3/8" roof I’ve ever seen. This was the only joint I saw that was actually broken, and the clips weren’t obviously loose.
A lot of the judging I did with my feet as I walked the roof. I was suprised that there wasn’t more deflection considering the conditions.

In retrospect I’m glad I included the comment about deferring to a structural engineer.

Don’t know about 40 years ago, but when I started in the construction industry 35 years ago we were installing H clips on roof decking. Nowadays roofs are decked with 7/16 plywood or OSB. That is what now passes for 1/2 inch.

Hi. to all;

Does anyone know of the History of the H-clip?
I have not found anything so far.
I know that Northern Maine might be behind the times, but I did not see H-clips being used until about the early 80’s.

Thanks in advance.