Shingles replacing shingles over gypsum board

We have a restoration contract on a nursing home with gypsum decking over steel truss work. The insurance company has ever so gracefully, sent out a scope paying for absolutely nothing but 1 layer of 20s off and on and some pipe jacks using the wrong price list missing every accessory and the 2nd layer among everything listed below.

Here is what I Know

The roof currently has 2 layers of 25 year fiberglass shingles nailed directly (1.75" galv nails) to the gypsum boards, no felt or wood anywhere but the owner of the building seems to think there is some sort of membrane under the original layer of shingles that cant be damaged during the tear off.

They have also stated that the manufacture of the gypsum product is no longer in business and they have used elevator shaft fireboards to replace a section of the sheathing on the roof before. I could not find any sort of name in the attic or from above of the product but I do have an email in requesting how they knew what it was to know they were out of business.

We removed some shingles today and saw nothing membrane related, just the 2 layers of shingles.

The tenants/insured’s, whom are triple net leasing the structure, have said that it was built (in 1985) with no wood to avoid needing attic sprinklers and all the drama that comes along with them and that no wood can be attached to the structure because they will then be required to have said sprinklers installed. I have a call into the building systems engineer they referred me to in order to clarify all of this but have not heard anything back

CertainTeed as well the makers of every brand of gypsum board that I could currently find installation instructions for online call for wood sheathing to be installed to the gypsum in order for the shingles to be warranted and installed correctly, obviously if this is done it brings up the sprinkler issue if it is an issue.

I guess what I’m looking for is any type of info anyone that has done one of these has to offer.

Is there a sheathing option that is not wood based that is acceptable to the shingle manufacturer?

Has anyone dealt with Guide One insurance and were you able to supplement for code upgrades?

Does anyone know if the sprinkler rule is accurate (NC)?

Any other advise? Its only an 880 sq job and with all this drama id rather just keep plugging along on my regular residential stuff if it gets too dramatic but the salespeople will definitely be pissed, they have been on mental vacation since the day the contract was signed on it

I have dealt with something like this before when I was still in the union prior to going out on my own. It was an elementary school in Mass. & new construction. This was the scope; install adhedsive to the metal decking, install a vapor barrier to the adhedsive, install Densdeck gypsum with 3 inch plates & 1 7/8’’ screws to the high ribs of the metal decking,( the gyp is for the fire rating) then do the samething but with vented r board, (that’s isoboard with plywood attached to that) with longer screws ofcourse, then Grace H/T ice & watershield, & finally the shingles! You can’t just nail shingles to gyp with metal decking underneath & a vapor barrier underneath! The shingles won’t hold! They’ll blow right off! There has to be plywood somewhere or somekind of wood! Even if you could nail to gyp you’ld puncture the vapor barrier! Or the roofing nails would hit the metal decking, be high nails, & eventually work through the shingles. The estimator, insurance adjuster, someone, or all of them are missing? or overlooking something?

the original roof had blow offs all over so 5 years ago they paid for a 2nd layer to be installed. Best guess I have is fire rated plywood over the gypsum. The gypsum is 2" thick and the nails are 1.75"

Ya, after I commented earlier I was trying to think back to 2000 when I was on that project & remember if it was 2 layers of gyp or not? I think you’re right? It might of been 2 layers of 5/8’’ or 3/4’’ gyp, I don’t recall but I know it was thick & I know it was overkill though.

If there are no sprinklers my local code requires a ‘thermal barrier’ between the interior space and combustibles. The thermal barrier can be many things including gypsum board. Shingles are certainly combustible, i’m not sure why plywood overtop of the gypsum wouldn’t be allowed. I think someone is misinterpreting the code. A call to the local fire marshal may help since they tend to be the final word on these kinds of issues.

This sounds like it is noncombustible construction, which is a whole other kettle of fish that I’m not wholly familiar with. Maybe it would be better to go with a torched/adhered modbit or EPDM?

Yes, its noncombustable type 2 construction

Right now I’m working on a high rise in downtown Boston & I did notice the plywood has a stamp on it. It said pyro free or pyro proof something like that. I remember now, pyro resistant is what it said.

You can get class a rated plywood for about 30 a sheet and class c for about 23, unclear to me currently if that will change the buildings non combustible status, which is not allowed.

GAF will let me apply the shingles directly to the gypsum as long as the nails have a 40lb pullout or higher. Tried to post the link to their tech pdf and the site wont let me.

All I need to do now is get the supplements approved (a mere 80k) and have the city county and state approve my building plans.

USG gypsum requires the old nail holes be patched with their version of mud. Still waiting on pricing and how to bill for it, if anyone runs into this in the future

that’s crazy! so u might as well skim coat the whole roof or ice n water seal the whole damn roof!

Ugh, what as asshole of a job. There must be steel deck below the gypsum, or some sort of support? Otherwise I can’t see it holding up to point loads very well. It will be hard to not damage the gypsum during tear off too. I imagine if they’ve been having leaks that parts of it will be mush.

Mush? Friggin’ apple sauce.

I think a shingle manufacturer would prefer to see their shingles applied to a nail-able substrate, which I’m pretty sure gypsum board is not…

Gaf is the only one that allows it. I haven’t figured out what to replace any bad planks with but I will if I can get the ins to pay me enough to mess with.

It has to be hand nailed with 1.75" nails too

Just steel rafters and possibly some steel running east to west between the planks. It’s gypsum top to bottom

I got the job to pay enough to mess with, shingles should be here next week

Be sure to get some pictures!

I’m running into the very same thing here in Ga on a job. What was the final verdict? GAF is telling me that the 40lb of pull has changed. They now want manufacture to tell the type of nails. Cant find manufacture. The building has 400 sq on it and I don’t want to take any chances. Any help would be greatly appreciated.

We did a school w/ a gypsum deck about 15 years ago. Required hand nailing these crazy looking nails that were split down the middle and barbed. They cost so much, you’d think they were made of copper.