Home construction--exterior sheathing mix-up

My builder’s standard sheathing for the exterior walls and roof is 7/16" OSB. I paid extra to have the roof upgraded to 1/2" (actually 15/32") OSB. The former has a span rating of 24/16, and the latter has a span rating of 32/16.

The framers screwed up. They used the 1/2" OSB on the exterior walls, until they ran out, and then started using 7/16". They then used 7/16" OSB on the roof.

I just brought this all to the builder’s attention. He’s asking me if I want them to rip off the roof sheathing and replace it with the thicker sheathing, and I told him yes.

My question then is: should I worry about the varying thicknesses of the sheathing on the exterior walls? They differ by 1/32" (1 mm). If I ask them to make them all match, they may just pull off the 1/2" and replace it with the 7/16", instead of vice versa. Or if I wish, they’ll leave it, but I’m then stuck with varying thicknesses.

Thanks!

I’m not a general contracter but have worked with many. Not sure if this applies to your problem but sometimes if 2 or 3 different crews from different places get involved , having to many people around can cause problems. You may want to talk to a siding expert if you can find one in your area, he/ or she may be able able to help you find another cost effective way to solve your problem.

Also, do you think making them replace the roof sheathing is a good idea? Will it damage the roof trusses?

This whole thing is not costing me anything more than aggravation. I have a lump-sum purchase contract with the builder. (I had to put down 10%.)

My choice for the exterior walls is to have mixed thicknesses, or all uniformly thinner (7/16"), the way it was supposed to be. Is it in my best interest to have them replace the thicker 1/2" sheathing panels with thinner 7/16" panels?

I’d say yes robby the idea of replaces them sounds like your best bet, especially if it’s not going to cost you anymore.(AFAIK this sounds purely like the contracter’s mistake not anyone elses.) I’d say replace the 1/2" with 7/16" that just makes everything less complicated and in home building/renovation less complication usually doesn’t mean low quality or bad work.

Your wall sheathing thickness mixup is not critical. It will never be apparent underneath your siding, and structurally makes no difference. 7/16 on the roof may require clips, depending on your truss spacing, although at 24" spacing probably doesn’t. Check your local building code.
Finnie- carpenter for 30 years.

As a GC, I’d make it right and not ask you any questions.

Thanks for the replies.

With respect to the roof, it’s occurred to me that the builder may offer to install another layer of OSB sheathing over the 7/16" roof sheathing they already installed to avoid having to rip off the first layer of sheathing. Is this a good idea, or should I have them remove the existing 7/16" sheathing and replace it with the 1/2" sheathing?

If they install another layer of sheathing, with they be able to find the roof trusses to line up the nails?

Sorry for the bump, but the builder wants me to give him a call back this morning so he can propose his solution to fix the sheathing problem.

If he proposes to double up the sheathing, should I let him?

OK, I talked to the builder, and he has offered me three options to address the 7/16” OSB on the roof.

Option #1: Rip off the 7/16” OSB and replace it with 1/2" OSB as in the original plans. (This is obviously the most painstaking option.)

Option #2: Upgrade the architectural shingles from 30-year to 50-year (normally a $1,000 upgrade charge), plus a $250 change order credit. (My concern here is that shingles aren’t really a structural member.)

Option #3: Add a second layer of 7/16” OSB to the existing layer of 7/16” OSB sheathing. The builder could not guarantee that they would be able to hit all of the trusses, but they would try to.

Here’s some data on the roof: the roof trusses are 16” O.C. (I upgraded from 24” O.C.) For the original 24” O.C., the roof was designed for 10 psf. With 7/16” OSB, I’m currently at 4 psf, and if they add a second layer of 7/16” OSB, that will put me at 5.5-6 psf.

I asked for 24 hours to make a decision. What do you folks think? I guess I’m leaning towards Option #3. Now that I think about it, I wonder if I can talk him into adding a layer of 3/8” or 7/16” plywood instead…

Ask the builder if the edges of the decking are supported or not. Using tongue in groove material (which I doubt they did, otherwise, why the mix up in sizes?), H-clips, or blocking (usually 2x2 wood) counts as supported. Suported means a stronger roof, a very strong one since you’re already at 16s rather than 24s.

If so, or if he will do so retro, then go for option #2.

In option 1 you run the risk of a halfassed job being done (sad but true fact of life). Option 3 adds more weight than strength imho.

Is there any 3rd party there you can ask for a non biased opinion? You’re paying extra, you should get extra, one way or another.

As usual, without being there to actually see anything, YMMV.

P.S. if your contractor is anything like Dances or the people I’ve worked with, he wouldn’t have asked, he just would’ve made right, so I’m a little bit worried over all. I strongly suggest a 3rd party be consulted.

The difference seems so inconsequential for most any conceivable scenario. My approach would be to come up with Option #4: Have the contractor upgrade something else, giving you, say, 75 percent of the cost of tearing off old for new, including labor.

I do know that homeowners are advised against re-refooing their houses with a third layer of asphalt shingles. Adding a second layer of sheathing would seem to make it even less load tolerant, unless I’m missing something big here.

I’d call a major university and ask a structural engineer/architect.

OK, I’ve been thinking about this all day.

They didn’t put edge clips or anything on the 7/16” OSB already installed.

Everything I’ve read indicates that 7/16” OSB is the bare minimum thickness to meet code, albeit with 24” O.C. roof trusses. Most builders recommend 1/2” plywood/OSB at a minimum, and prefer 5/8”. Everyone seems to prefer plywood for roofs as well.

I’m concerned about Option #1, because I’m afraid the framers will do a careless job if they are forced to rip off the first layer of sheathing.

I’m not inclined toward Option #2, because I think the 50-year shingles simply add more cosmetic shadowing, more weight (about 0.7 psf), while gaining nothing structurally.

I’m concerned about Option #3, because I think adding another layer of 7/16” OSB adds a whole lot of weight (between 1.5-2.0 psf) for the strength gain.

So that being said, I’m thinking about asking the builder to add a layer of 3/8” plywood. The weight is much less than the OSB (about 1.1 psf), and plywood is supposed to be better for roofs. Also, the cost for 3/8” plywood is comparable to 7/16” OSB. If he refuses this, I think I’ll go with Option #1.

Hey well. Sometimes as contractors we screw up. It serves as a reminder to be more diligent the next time.

50 year shingles are a heavier product. Before you sign off on this, ensure that that manufacturer of the shingles is OK with that sheathing thickness and span, as well as meeting applicable building code for roof assemblies.

This is scary. The addition of anti uplift engineered fasteners as well as strict standards for nailoff in the wake of hurricane/tornado damage over the last few years makes me question the viability of this method. Not only can’t he guarantee that he’ll hit the truss members, but what nails are planned? 8d is definitely no good. A 12d at minimum would attach the new sheathing plane, if the original nailoff schedule is met. I’d accept this if: A) A PE signs off on the plan, B) 12d or 16d nails are used and it is verified that 90% or better truss member imbedment is achieved, and C) the contractor applies a zigzag layer of polyurethane construction cement between the two sheathing layers, placing new sheathing breaks horizontally 32" off existing, and vertically 24" off existing.
Here’s a data sheet in .pdf of the brand that I’ve used for a number of years.

Here’s some data on the roof: the roof trusses are 16” O.C. (I upgraded from 24” O.C.) For the original 24” O.C., the roof was designed for 10 psf. With 7/16” OSB, I’m currently at 4 psf, and if they add a second layer of 7/16” OSB, that will put me at 5.5-6 psf.

I asked for 24 hours to make a decision. What do you folks think? I guess I’m leaning towards Option #3. Now that I think about it, I wonder if I can talk him into adding a layer of 3/8” or 7/16” plywood instead…
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For what it’s worth, I called the APA – Engineered Wood Association hotline. This is the organization that rates plywood and OSB.

Of all the options, the technical support guy recommended the overlay of another layer of 7/16” OSB. He said it will add 1.4 psf and result in a very strong roof. He said specifically to not use construction cement, as it won’t allow for contraction/expansion.

The builder already said they would offset the new joints. I’ll tell them if they do this option, they need to use bigger nails.

That’s an interesting position. Why would two thicknesses of the same or similar product behave differently when exposed to the same temperature shift?