Townhouses - Fire-Rated Walls Jogging in Plan & Windows

[rosegamble]

Hello All.

Hoping to get some feedback on this.

Please see plan diagram below. We have three townhouses, not sprinklered. IRC 2021 is the code here. The 2 hour wall is indicated in red (R03.2.2).

SCENARIO 1: Now let's say all three units have lot lines between the units (lot lines indicated with the orange dashed line). As the units jog in plan, we are guessing the exterior walls indicated in blue must be 1 hour rated in the blue locations under Table R302.1(1), which stipulates that walls on property lines must have a 1 hour rating. In this case, openings would not be permissible in the "blue zone" per Table R302.1(1).

SCENARIO 2: Let's say all three townhouse units are on one large lot, shared in an HPR format (horizontal property regime). Are the exterior walls indicated in blue thus not required to be rated? And window openings in the blue section would be permissible?

Am I understanding this correctly?

Thanks!
Rachel

 

[rosegamble]

Hi All. Just following up on this. A quick google search shows that the front facades of townhouses often jog, so this must be an issue encountered before.

 

[classicT]

This is a bit of a hole in the code. There is not any clarification spelled out that I am aware of regarding the horizontal continuity of the double/common wall separating townhouses. You may get several opinions, even conflicting opinions, given the lack of clarification found in the IRC.

That said, IMHO I would place an imaginary lot line between the units if they were all constructed on the same lot. Thus, in scenario two, with an imaginary lot line, you end up at the same requirement as scenario one. 1-hr wall where the unit extends parallel to the separation line.

 

[mtlogcabin]

Thus, in scenario two, with an imaginary lot line, you end up at the same requirement as scenario one. 1-hr wall where the unit extends parallel to the separation line.

That is how we do it also. The one-hour wall is rated from both sides.

 

[steveray]

Gets even more complicated when you have overhangs and soffits in that area...

 

[chief-inspector]

The code has changed some on this type of thing but I would always spec out a 2 hour shaft wall between the units and not mess around with one or two hour wall because it's only a matter of an additional 5/8 x on each side to get 2 hours. When you get into commercial code on this type of construction which would be an apartment or condo firewalls have to extend horizontally on each side of the structure and there is a difficult to understand provision about the wall-butting into that firewall. Go to the commentaries to understand any of this type of thing.