OSB fire rating?

New construction contractor wanted to argue the fire wall between garage and living space
Said OSB is fire rated?
anyone been there before?

Regular OSB is class C and no good for exposed walls as a fire wall.

Fire rated OSB is available but very expensive. I have not seen any of it.

I doubt it is there, it would cost more than the regular OSB and sheetrock.

Check these out for your information.


Marcel:) :slight_smile:

Wouldn’t the contractor be able to show the receipts from the OSB showing that it was fire-rated?

Thanks Marcel for the OSB Guide. :slight_smile:

Wendy, If he had purchased fire rated OSB he would have had the reciept in his pocket…

Any builder that purchases that will definitely know that he will need to prove its rating later. Any site that has sheetrock workers present will not need to purchase fire rated OSB.

added with edit:
Having trouble with the pdf documents from Marcel’s post…
It looks like the chart that compares sheetrock with osb refers to the sheetrock as type X or higher and appears to show that OSB is the same rating… Anyone get these to load without aborting?

I had the same problem with aborting so I quick printed the OSB FIRE PERFORMANCE before it aborted.

Anyway a 16" oc stud wall with mineral wool insulation and 19/32", 5/8" OSB both sides has a 14 minute rating. :shock:

Not much.


David, what is your opinion on 7/16 regular OSB?
Equivalent to Type X sheetrock or not?

Type X sheetrock -5/8- is top of the line and is a National F/C Standard. I wouldn’t want to see anything but Type X, installed as a firewall.

I’m just posting a site that references OSB as an approved firewall.

Thats interesting…

Sheetrock must have the joints sealed but its ok to butt OSB together for a fire wall?

I have now started recommending a smoke detector in garages.
I have had mine for 4 years now and not one false alarm.
Due to many electrical panels being in garages and the firewalls it is an early warning smoke alarm.

here is a link about garages http://homestore.com/HomeGarden/GarageDriveway/Inspection.asp?poe=homestore


There seems to be some confusion here. The Table in


is in reference to tested assemblies that included gypsum as part of the assembly. These tests were done to demonstrate that OSB and plywood had similar fire characteristics and not to confirm the use of OSB as a firewall material.

Bottom line:

**OSB is NOT a substitute for 5/8" taped Gypsum for the purpose of fire separation.


Thanks Mike !

I can’t open that document for more than 10 seconds then it gives an error and has to close.

As a summary, any Type X sheetrock is ok
Is 1/2 or 5/8 regular sheetrock (taped with one coat) ok for firewall or does it depend on the AHJ ?

1/2 was ok around here in 2001 and still may be, not sure.

This might help.


One-Sided One-Hour Fire-Rated Wall Assemblies
In late 1997, Underwriters Laboratories Inc. (U.L.) promulgated a new fire-rated wall design that recognizes both oriented strand board (OSB) and plywood panels for wall sheathing in one-hour, fire-rated, load-bearing exterior wall assemblies.

New fire-rated wall design - U.L. Design U356

  • One-sided assembly, rated for fire from the interior face of the wall
  • 7/16-inch or thicker plywood or OSB sheathing, installed vertically or horizontally on exterior face of wall (joints must be blocked when panels are installed horizontally)
  • Studs spaced 16 inches on center
  • Code-approved exterior finish
  • Glass fiber insulation (R-13 minimum) or mineral wool insulation; minimum 3-½ inches thick
  • 5/8-inch Type X gypsum wallboard on interior face of wall
  • Fire-rated walls which are rated only from the interior face are permitted under the 1996 National Building Code and the 1997 Standard Building Code when there is more than five feet of horizontal fire separation distance.


Marcel :slight_smile: :slight_smile:

The issue of concern is the burn through rating(time).

But as in all code compliance issues the local AHJ rules. Allways good to keep that in mind.:shock:

Hope the following helps.

What’s the difference between “regular” and “type X” gypsum wallboard?

ASTM C 36 designates two types of gypsum wallboard, regular and type X.
Type X wallboard, which is typically required to achieve fire resistance ratings, is formulated by adding noncombustible fibers to the gypsum. These fibers help maintain the integrity of the core as shrinkage occurs providing greater resistance to heat transfer during fire exposure.

By ASTM definition, type X gypsum wallboard must provide: not less than a one hour fire resistance rating for 5/8" board or a 3/4 hour fire resistance rating for 1/2" board applied in a single layer, nailed on each face of load-bearing wood framing members, when tested in accordance with the requirements of ASTM E 119, Methods of Fire Test of Building Constructions and materials.

Additionally, the Gypsum Association requires 1/2" type X gypsum board to achieve a one hour fire resistance rating when applied to a floor ceiling system, as described by GA File Number FC 5410, in GA 600, the Gypsum Association Fire Resistance Design Manu

Marcel’s post while informative does not address the issue at hand.

The issue is What is required between the gargage and the interior dwelling space. :slight_smile:

I would think in my mind that if a garage space has to be 1-hour rated to protect the house, that it would only make loggical sense that it continue up to the roof assembly.

Regular Gypsum Board affords a degree of natural fire resistance. The fire resistant noncombustible core is coposed mainly of gypsum.

The term “1 hour fire-rated system” is generally used to refer to a system that has been shown in a carefully controlled laboratory test to be capable of limiting the transmission of high temperatures to a specified maxumum, and to meet other requirements, for a least 60 minutes. ASTME119

What we all need to understand, is that Fire Rated Assemblies are based on standards like NFPA 251.

5/8" Type X Wallboard has NO fire rating.

Fire ratings are assigned to a COMPLETE ASSEMBLY that may include 5/8" or 1/2" wallboard as a componet.

Ratings established by UL might list such wall assemblies for one hour as having a min. stud depth of 2 1/2" and 1 layer of 1/2" thick drywall with 2" thick insulation. That is the assembly.
A one hour rating using 5/8" drywall would require a min. stud depth of 3 5/8" and one layer of 5/8" drywall.

The fire ratings of the above posts, as mentioned for the APA OSB, is comparing their burnings charisteristics with regular plywood. The time of igition compared to drywall does not compare and this product would not qualify as a fire rated 1 hour protection on it’s own.

Hope this helps clarify this confusion.

Marcel :slight_smile: :slight_smile:

** **http://www.gypsum.org/

** www.bfcacademy.com](http://www.bfcacademy.com)**

I agree completely. Alternately you could apply Gypsum wall board and non framing supported taped joints to the ceiling of the garage to provide the separation.

You also need to be careful that any access points such as drop down stairways maintain the fire separation. Its common to see a plywood panel as part of the stairway in the garage ceiling. This type construction by itself compromises the protection provided by the gypsum on the ceiling.


Strawbale is reputed to be tested as 2-hour fire rated.

Anyone have any first hand knowledge about this?

At what moisture content? I doubt if any real data exists on that from a reputable source.

An interview with Bruce Glenn of Terra Sol Eco Homes, LLC. also the current president of Norwest Eco Building Guild, Peninsula Chapter and one of the authors of the “Built-Green” guildelines for Jefferson county Homebuilders Association in Washington State.

He states that Canadian testing, as well as New Mexico, Arizona and California testing all prove that a plaster strawbale has a 2-hour firewall. This being over five times what international builders require for and exterior wall, or four times for interior walls in conventional houses.

He can be reached at www.strawbalehomes.com .