Anyone ever replaced only some 3/8" plywood with 1/2"? Was the transition noticeable?

I have an old house with 3/8 plywood, on joists spaced 24" oc. You can feel the bit of give of the plywood when walking between joists, but its otherwise been fine. I do think its thinner than ideal, given the soft feel, but don’t have the budget to replace all of it on the house, and the contractor wasn’t interested in doing it either, so I’m opting not to replace what isn’t damaged.

However there is a large repair being made with many sheets in a particular area being replaced (and possibly a few scattered ones here and there). With 1/2 being the standard now to my knowledge, I’d hate to go to all the work and expense and put 3/8 right back on. I’d rather just use 1/2 if I knew there were no issues.

I heard a couple roofers say different things. One says you would never even see that 1/8 inch difference after having all the shingles on and should just use 1/2 for anything new. Others say you would see that 1/8, and that the edge could be a problem area. Not sure if any of these opinions came from real experience or just guessing though, and I haven’t found any sort of pictures or hard evidence to see it myself.

Anyone ever done this before, and have any input if it would be better to just stick with 3/8", or transition to the 1/2"? I’m also leaning towards possibly using 7/16 or else using 1/2 but tapering the edges down with a belt sander to make a closer match.

You cant get “1/2 inch” anyways.
It is actually the 7/16 or 15/32.
No, you wont notice a difference.
No, it wont be a problem.

If you want to be anal about it
You could lay a shingle up against any tall edges to plain it out.
Do that before You install underlayment.

Edit… i should mention im anal.
I assure you, it will be perfect.
If one shingle thickness does not plain it out,
Use Two.
But i dont think you’ll need to.
If a second shingle is needed, cut that one a little shorter to feather out the other side.
Cut it an inch shorter so you feather out the other side.


You wont notice it at all. My in laws bought a shed from the local college,built by students. They used 1/4" osb as the roof sheathing, held up much better than you would have thought. When I replaced the roof, I used 7/16" osb to replace the couple of bad sheets and the little bumps are nearly impossible to notice.

Thanks. As a follow up, in case anyone else is in this situation. I replaced many sheets with 1/2 inch, both in horizontal rows like across the front, and some runs of vertical ones (which were staggered), as well as at least one solo sheet all by itself. I could not see the difference at all in my case, and definitely recommend just going 1/2 inch. This was with 30 year architectural shingles.

Believe it or not, you couldn’t even see the 1/8th difference a lot of the time even when up close. The old sheets were a bit worn out, and possibly the edges swollen a bit, or not sitting too nice, so many times the 1/2" actually ended up sitting pretty close to flush. So even before the shingles were on, you really couldn’t realistically see the difference from the ground or often times, even when right up there working you couldn’t really see it. No need to worry about tapering any edges or anything.

Perhaps if the roof was dead perfect flat and new, maybe you would see something, but in my case (and I’d imagine almost any case where 3/8th is used), it is an old house and there are probably larger dips and bumps elsewhere than any 1/8th plywood difference. In fact, the areas that show the most are older 3/8th sheets that were a bit aged but we didn’t have time to replace them. Those show a little sag.

There actually were a couple sheets that were replaced with 3/8, since we had both sizes on hand. I can definitely say there is a world of difference in the solid feel of the 1/2.

There was one advantage of 3/8. It is easier to replace a piece in the middle of all others pieces with 3/8 while keeping all H clips on both sides, since 2 people can work together to flex it into place, which wouldn’t be possible with 1/2". With 1/2", according to all the carpenters and roofers, as well as my own knowledge, there just isn’t a way to get all the clips on without bending some of the tabs out of the way.

Overall, I’d say from my personal experience, no need to even think about this as hard as I did. Just go 1/2" for any new pieces.