Best way to determine fire rating

Originally Posted By: jonofrey
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I’m searching for the best way to determine the fire rating of existing party walls in townhomes?

It seems to me that it is difficult to determine without destructive testing unless there is some kind of historical construction documentation.


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Originally Posted By: chorne
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Hi John,

I will measure the door jamb thickness, if there is a door opening,
or take the cover plate off of an outlet and sometimes
you can tell that way if the rock isnt completely tight around the


Originally Posted By: gbeaumont
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hi John,

I tend to agree with Carla's comment, but another area that is some what of a giveaway is the attic space, where normally the party walls are some what unfinished.



Gerry Beaumont
NACHI Education Committee
e-mail :
NACHI phone 484-429-5466

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"Education is a journey, not a destination"

Originally Posted By: mpetner
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Walls located on a property line between buildings usually don?t have openings. These walls (party walls) are considered firewalls (as opposed to fire partitions, fire barriers, or some other fire rated assembly) and are continuous from the foundation to about 30? above the roof line. Given that, you may not find any penetrations. Floor framing is allowed to penetrate into party walls but there are provisions that need to be taken in that situation. If you do find a penetration through what you think is a party wall, then it may not be a true party wall after all. It may be some other fire rated assembly. In fact, the building may not be considered an R-3 use, which the IRC really only deals with.

If, by chance, you do know how the wall was made, you can check the ?Fire Resistance - Volume 1 - With Hourly Ratings for Beams, Floors, Roofs, Columns, Walls and Partitions? publication. It?s a publication from Underwriters Laboratories, Inc. This pub gives ratings for numerous fire rated assemblies - more assemblies than you can shake a stick at!

Originally Posted By: Ryan Jackson
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Michael: the term R-3 does not esist in the IRC. There is no use, there is no occupancy classification in the IRC. R-3 is an IBC term refering to a dwelling built under the provisions of the IBC. An IRC structure is not an R-3, it is an IRC structure. Sorry about the thread jack.

As far as the fire resistance goes, look at the drywall and see if you can see "hairs" where it has been cut (at maybe an outlet box), if you see the little things that look like hairs, you have type X wallboard, which must be taken into consideration when determing the fire resistance rating.

Ryan Jackson, Salt Lake City

Originally Posted By: Blaine Wiley
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How do you see a firewall between townhouses by opening an outlet box? The only place I’ve ever seen them was in the attic or in an unfinished basement. In VA the firewall (partition wall or party wall) was usually (as I recall) 2" drywall at each unit (4" total) or a cement block wall. Most builders went the drywall method because not only was it cheaper and less labor intensive, but also provided better soundproofing between units.

On the insides of the firewall on each unit was a 2x4 frame wall. If anything less was used (some cheap builders used 1x2 or 2x3) it was easy to spot because they did not use recessed receptacle and switch boxes mounted on the party wall so as not to breach the firewall.

We used to write up breaches in the firewalls of attics frequently, such as torn drywall, missing seam tape, etc.

I haven't seen a townhouse for two years, so If my memory is incorrect, just forgive me, I'm heading for the beach. ![icon_biggrin.gif](upload://iKNGSw3qcRIEmXySa8gItY6Gczg.gif)

Originally Posted By: mpetner
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From a plan review standpoint, the first step is to determine the use and occupancy of the structure (R-1, 2, 3, S-1, M, F-1 etc). If it?s a one or two family dwelling unit not more than 3 stories above grade plane, it should be reviewed using the IRC. If its, for example, a single family 3 story home with a very large mezzanine, it should be reviewed under the IBC. Most single family dwellings are considered R-3?s in the IBC. The IBC then tells you to review the dwelling unit using the IRC. That?s why I said the IRC mostly deals with R-3?s. I know there is no use and occupancy mentioned in the IRC.