Attic fire separation questions

[John Kogel]

A client asked me "what is the fire rating?" of the taped and mudded drywall barrier in his townhouse attic.

I said it meets the requirements. Is there a better way to answer this question about "fire rating"?

The drywall covers the roof truss common to the two attics, so that is correct. For roofing, they have open plank strapping, roofing paper and cedar shingles. There is no drywall there, so fire will spread across the roof fairly quickly, I'd say.

Another question - where seams in the drywall fire separation wall in an attic are not backed by wood framing, are the seams required to be taped and mudded, that is on the exposed backsides of the drywall?

[Jerry Peck]

Sounds like you are describing a draftstop wall instead of a firewall.

Down here ... A 1 or 2 hour firewall would be required.

[Fred Weck]

Jerry is right, it sounds like a draftstop. A firewall would either extend through the roof with a 30" tall parapet or would turn ad continue under the roof sheathing. Draftstops do not need to be taped if the joints are over framing or are tight. A firewall would need to b tape if that w s a part of its listing approval.

[Jerry Peck]

The drywall covers the roof truss common to the two attics, so that is correct.

The above and this:

Another question - where seams in the drywall fire separation wall in an attic are not backed by wood framing, are the seams required to be taped and mudded, that is on the exposed backsides of the drywall?

Cause me to think there is drywall on one side only. That would be a draftstop wall, not a firewall (a firewall has gypsum board on both sides).

Also, a firewall would require, as Fred said, ether the firewall going through the roof with a parapet wall above, or the underside of the roof being protected with gypsum board out at least 4 feet each side of the firewall.

[John Kogel]

Thanks Jerry and Fred.

I was under the impression that the wall is there to slow the spread of a fire, and a draftstop would do that.
Sometimes in a condo building we will see the concrete block wall extending up through the roof. OK, that will stop a fire.

[Jerry Peck]

I was under the impression that the wall is there to slow the spread of a fire, and a draftstop would do that.
Sometimes in a condo building we will see the concrete block wall extending up through the roof. OK, that will stop a fire.

With a condo, the structure is a single structure, not multiple attached structures like townhouses are.

With a condo or apartment buildings (down here) a draftstop wall is required in the attic above every two units or 3,000 sf, whichever is less, for 4-stories or less, every dwelling unit otherwise, and must be in line with the separation walls below.

With townhouses, which are separate but attached structures, they are separated by a firewall of either 1 or 2 hour rating (some variables apply, that is why the two options). With townhouses, the intent is that one of the attached structures can fall down/burn down but the other formerly attached structures will remain standing (for at least the 1 or 2 hours of the separation wall anyway),

Almost sounds like your structures 'up there' are constructed the opposite? Strange.

[John Kogel]

Not really opposite but the rules are certainly less stringent for townhouse fire separation. Or were so, because a lot of these buildings were built before the rules were sorted out, i suppose.