Two -Family Townhouse Fire Separation

This two family townhome has a shared attic. The access from where I took the picture is in the garage. The garages for both units have 5/8" drywall on the dwelling walls, the shared garage walls and the ceilings.

In the pictures below, there is drywall extending up between the units (not mudded) but stopping at a section of OSB decking lower than than the actual roof. Aside from the lack of mud at the drywall joints, is this separation adequate or should it be extended to the roof?

If the attic is over both units and this is not a detached garage, then IMO yes the firewall should extend to the deck and I would write it up.


Should that wall be extended to the roof line between both the dwelling and the attached garages or just the dwelling portion since the garages have their ceilings drywalled?

I was curious so I looked it up. Must go to the underside of the sheathing. They are not going to be happy with that one.

R302.2.2 Common Walls

Common walls separating townhouse units shall be assigned a fire-resistance rating in accordance with Item 1 or 2 and shall be rated for fire exposure from both sides. Common walls shall extend to and be tight against the exterior sheathing of the exterior walls, or the inside face of exterior walls without stud cavities, and the underside of the roof sheathing.


Thanks Mark. I did read that too. I guess I am stumped because of the presence of the lower “roof decking” that the wall currently goes to.

Was there an addition to this building?

It’s possible they just left the original sheathing in that lower area. This might be something you’d want to touch base with the Local AHJ and open that can of worms. A fix like that isn’t going to be cheap and someone isn’t going to be happy with you for calling it out.

I know in my home, the monkey’s that built it left a bunch of sheathing in places where it doesn’t belong on the trusses making it a pain to move around up there. It’s like they built the house, then added the garage but I know without a doubt it was all built at the same time because they are cookie cutter homes and the garage has the air handler and water heater.

No, this was not an addition; the property is less that a year old.

This seems to me that the local code inspector thought it was ok then and they have ultimate authority.

Joe does Wisconsin use the IRC or other?

I would check with the AHJ and maybe visit them with your photos if you can.
It seems like a reverse gable above the common roofline.
That is an odd ball situation, IMHO.

I agree with Mark:


Thanks Larry. Wisconsin has their own Uniform Dwelling Code. Fire Separation is referenced here:

From the code:
(2) Dwelling unit separation.

(a) General. In 2-family dwellings, dwelling units shall be separated from each other and from shared tenant spaces including attics, basements, garages, vestibules and corridors.

(b) Attic separation. Dwelling units with attic space that extends over both units shall be separated in accordance with one of the following:

  1. `Complete separation.’ The units shall be provided with wall construction under par. (d) that extends all the way to the underside of the roof deck.

  2. `Vertical and horizontal separation.’

a. The units shall be provided with wall construction under par. (d) that extends to the dwelling unit ceiling and ceiling construction under par. (e).

b. Dwelling units using this method of separation shall provide attic draft stopping under par. (f) that extends all the way to the underside of the roof deck above and in line with the separation wall.


Does it extend all the way up to the underside of the roof deck? Appears so.


Brian, to my eye, the 2 red arrows are at 90* from each other. So, it doesn’t appear to me that my white arrow would have the wall construction that goes to the bottom of the roof deck. I could be wrong in my visual acuity though.

Do you see what I think I see?



I am not sure what I see anymore. Your arrows helped in some ways.

But if you can just walk around this wall…what good is it?



None at all.

What does paragraph (d) say?

So far the language you posted says complete separation. That should include the garage attic as well. As @lkage noted, the drywall does not appear to go all the way up to the roof deck in the area marked in his picture, so if that area is over the adjacent unit, then it is wrong and needs fixed. Just because the garage ceiling is drywalled doesn’t mean squat. The interior has drywall on the ceiling. It’s all in the language of your AHJ and how it’s interpreted really, so to me, unless there is an exception to what you shared from the AHJ, call it out as in need of repair, keep the narrative simple.


That was my concern. I would think that the separating wall should go all the way to the roof as well as extend along the shared garage wall.

(d) Walls. Walls in the dwelling unit separation shall be protected by not less than one layer of 5/ 8-inch Type X gypsum wallboard or 2 layers of ½-inch gypsum wallboard or equivalent on each side of the wall with joints in compliance with sub. (1) (a) 2.

I appreciate everyone’s responses. I agree with the need for complete separation. I’ll write it up as such and if I can get a straight answer from the AHJ, I’ll post it here.


As @mdurante said “None at all”.


I think I see it now…is this right?

Yes, that is correct

…and this is a valley?

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It’s more of a shelf over the dwelling space.
This may give you a better idea of the roof slopes

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