garage wall fire resistance rating

Yes, my first post and it’s a question. I’ve been a builder/developer and GC for about 30 years and I think I know the codes pretty well. I always use 5/8 type X sheetrock on the garage side of any walls or ceilings common to living areas. I am completing a house that was foreclosed by the construction lender, and I’ve run in to a bit of a snag. The house does have a wall between the living space and gargage that consists of 1/2 sheetrock, 2x6 stud with fiberglass insulation, and 5/8 type X on the garage side. The local fire inspector (New Hampshire town) tells me that the wall in question must have TWO layers of 5/8 Type X on the garage side (local ordinance). Since the garage is already taped and painted, and the rated door installed, I’d rather not add a layer of sheetrock now. He did say that I could substitute any 1-hour rated assembly as long as I could show it was UL approved. I always thought the wall system I’ve always used is a 1 hour system, but where do I go to find it in writing to satisfy him?

BTW, I have read through several threads on this board, and I’m pretty impressed with the level of knowledge I’m seeing. I think from now on when one of my prospective buyers wants a pre-sale inspection I’ll insist that they use the services of a NACHI member.

Thanks in advance for the help.

Hello Joseph,

You can try and see if the New Hampshire town or county is listed. Hopefully this will save you a trip to find local AHJ’s requirements. The new Hampshire state building codes can be found at

If you are familiar with the IRC, IFC, etc. codes then you probably already have an electronic version of that.

As you know the AHJ’s can make the codes more restrictive. Hopefully you will find your answer within one of these references.

The code isn’t the question. The inspector showed me the local ordinance requiring either 2 layers of 5/8 on the garage wall OR another 1 hour assembly. I can’t economically install another layer or 5/8, so I have to prove my existing assembly (1/2 sheetrock, 2x6 insulated cavity, 5/8 type X) has a UL 1-hour rating. My question is where do I go to get UL standard ratings?

This may be helpful and more references here and here


You need a UL # that will show you the exact wall assembly that was tested.
Since you only have 1/2" layer on one side, you will find that your assembly rating is shy of an hour by 15 minutes.

If you do not want to add another layer, maybe painting it with No-Burn will satisfy the AHJ.

Marcel :slight_smile: :smiley: this shows most ratings, but none to solve your problem, sorry

That wall technically isn’t a 1-hour rated assembly, as it doesn’t have a 1-hour rating from either side. And the standard UL ratings assume the same finish on both sides of the wall.

Looks like it might be slightly over 1-hour from the garage side, and slightly under 1-hour from the interior side considering the drywall, wood framing, and wall cavity insulation. Therefore the entire “assembly” has less than a 1-hour rating.

However if the real concern is having a 1-hour rating from the garage side only (taking that as the “fire exposed side”), you may be able to get a local PE or RA to do whats called a component “calculated fire resistance” to possibly show it has a 1-hour rating from the garage side if thats what the local AHJ is concerned about and would accept.

JMO & 2-nickels … :wink:

That’s something I was not aware of. I’ll check with a PE I deal with and see if he can come up with something. Thanks.


You wrote the following:

Here in NY this statement is true, and not true.

For any municipality to exceed the building code, the interpretation/modification/restriction would need to be submitted to the NY State Department of State to be approved or the requirement is not legally enforceable.

I wonder is similar rules apply in other states.

Mr. Farsetta is correct, that in NY a local ordiance is not inforcable unless the more restrictive requirement is approved by the NY Dept. Of State. Call the Underwriters Lab in Mass. and see if they can give you a UL # for the intire assembly of the garage wall. Since the wall cavity is filled with noncombustible insulation there maybe an approved rating.