townhouse common wall

[hans@dha-architects.]

I'm doing a group of townhouse buildings and I'm detailing the common party wall between units, it's a double wall with two layers sheetrock each unit side with a 2" gap between walls - typically when you see this wall detailed the gap between walls is continuous aside from mineral wool fire blocking at each story, is there any reason to not connect the walls within the cavity, so instead of having double 2x4 top plates at each wall, the upper plate could be a 2x10 (cut down to 9"), there by serving as fireblocking and connecting/stabilizing the two walls as well - I worry that the only place the two walls are restrained are at the first floor slab and with the roof sheathing. It wouldn't affect the structural independence of the two walls as it's within the sheetrock enclosure, only potential downside is noise/vibration could potentially transmit to adjacent units

 

[steveray]

Bearing wall or no? You might have a hard time convincing the inspector of this, but 2 or 5 should work:

R302.2.6​

Each townhouse unit shall be structurally independent.

Exceptions:

1. 1.Foundations supporting exterior walls or common walls.
2. 2.Structural roof and wall sheathing from each unit fastened to the common wall framing.
3. 3.Nonstructural wall and roof coverings.
4. 4.Flashing at termination of roof covering over common wall.
5. 5.Townhouse units separated by a common wall as provided in Section R302.2.2, Item 1 or 2.
6. 6.Townhouse units protected by a fire sprinkler system complying with Section P2904 or NFPA 13D.

Which town?

 

[hans@dha-architects.]

Bearing wall or no? You might have a hard time convincing the inspector of this, but 2 or 5 should work:

R302.2.6​

Each townhouse unit shall be structurally independent.

Exceptions:

1. 1.Foundations supporting exterior walls or common walls.
2. 2.Structural roof and wall sheathing from each unit fastened to the common wall framing.
3. 3.Nonstructural wall and roof coverings.
4. 4.Flashing at termination of roof covering over common wall.
5. 5.Townhouse units separated by a common wall as provided in Section R302.2.2, Item 1 or 2.
6. 6.Townhouse units protected by a fire sprinkler system complying with Section P2904 or NFPA 13D.

Which town?

bearing - the 2 floor framing is bearing on it with fire hangers.......I guess my thought is if fire eventually makes it's way thru the double layer of sheetrock from one side into the wall cavity, the plate connecting the two walls is going to burn along with the rest of the wall framing.......I'm probably overthinking it, I'll just stick some rockwool in there

 

[steveray]

bearing - the 2 floor framing is bearing on it with fire hangers.......I guess my thought is if fire eventually makes it's way thru the double layer of sheetrock from one side into the wall cavity, the plate connecting the two walls is going to burn along with the rest of the wall framing.......I'm probably overthinking it, I'll just stick some rockwool in there

Ex. 5 likely gets you there...

 

[hans@dha-architects.]

bearing - the 2 floor framing is bearing on it with fire hangers.......I guess my thought is if fire eventually makes it's way thru the double layer of sheetrock from one side into the wall cavity, the plate connecting the two walls is going to burn along with the rest of the wall framing.......I'm probably overthinking it, I'll just stick some rockwool in there

Ex. 5 likely gets you there...

yes, I think you are right, no sprinklers and 2 hour wall.....it's in rocky hill by the way.......if that's the case, can the plywood subfloor of each unit penetrate the fire wall and connect the walls? I had initially planned to have the sheetrock be continuous from slab to roof with only penetrations being top mount fire hangers, but my engineer apparently needs it to penetrate the common wall and bridge the inner wall framing for his diaphragm calculations, but I can't find where it says the plywood can penetrate the sheetrock with this particular wall type

 

[hans@dha-architects.]

actually in the commentary it sounds like floor sheathing can penetrate the wall so floor diaphragms can structurally work

 

[steveray]

yes, I think you are right, no sprinklers and 2 hour wall.....it's in rocky hill by the way.......if that's the case, can the plywood subfloor of each unit penetrate the fire wall and connect the walls? I had initially planned to have the sheetrock be continuous from slab to roof with only penetrations being top mount fire hangers, but my engineer apparently needs it to penetrate the common wall and bridge the inner wall framing for his diaphragm calculations, but I can't find where it says the plywood can penetrate the sheetrock with this particular wall type

Michael is not bad so I hope that goes well....

actually in the commentary it sounds like floor sheathing can penetrate the wall so floor diaphragms can structurally work

That gets a little grayer as it is not in #2 but roof and wall sheathing is....

 

[hans@dha-architects.]

Michael is not bad so I hope that goes well....

That gets a little grayer as it is not in #2 but roof and wall sheathing is....

yeah, I can't find a definitive answer anywhere except that vague one in the commentary, I haven't done townhouses in a long time and can't recall how we handled it back then - probably didn't use a structural engineer back then either so weren't looking at diaphragms, we're going to show it bridging the common wall framing for now, but not connecting the two framed inner walls

 

[steveray]

It's the compound issue of the structural independence and the penetration of the rating....I thought they were working on this for 2024, but I don't see a whole lot new there...maybe 2027....

R302.2.3​

The fire-resistance-rated wall or assembly separating townhouse units shall be continuous from the foundation to the underside of the roof sheathing, roof deck or slab. The fire-resistance rating shall extend the full length of the wall or assembly, including wall extensions through and separating attached enclosed accessory structures.

 

[Yankee Chronicler]

I cannot envision how allowing the plywood subfloor to penetrate the separation wall and connect adjacent units could possibly satisfy the structurally independent criterion.

I haven't seen any townhouse type building in the past 20 years (or more) that didn't use a USG separation assembly (essentially shaftwall). Why aren't you using it?

 

[mark handler]

Thread 'Party Wall'

May 7, 2020

Hello Everyone,
Do you need a UL Floor/Ceiling (L563) rating in the cavity space of a UL rated Party Wall U305? Specifically in the area of the airspace of the Party Wall floor framing.
IBC 2012
Occupancy R-2
Construction Type 5-A Sprinklered

Thanks, Jeff

• nitramnaed
• Replies: 9
• Forum: Commercial Building Codes

 

[hans@dha-architects.]

I cannot envision how allowing the plywood subfloor to penetrate the separation wall and connect adjacent units could possibly satisfy the structurally independent criterion.

I haven't seen any townhouse type building in the past 20 years (or more) that didn't use a USG separation assembly (essentially shaftwall). Why aren't you using it?

we won't be connecting the two separate walls, but per exception 5 the townhouses don't need to be structurally independent....as for using shaftwall, I don't know, we've just always done it this way - not that I do them a lot, but I guess having the two hour rating in the middle allows you a lot more freedom with framing and plumbing

 

[steveray]

having the two hour rating in the middle allows you a lot more freedom with framing and plumbing

yep...The residential guys are scared of shaftwall, but it really is "easier"...

 

[hans@dha-architects.]

yep...The residential guys are scared of shaftwall, but it really is "easier"...

that's the worry, I don't know what kind of crew will be building this - maybe we'll switch it up later on, but I imagine it complicates things with the trades as I imagine you have to frame one wall up first then get the sheetrockers in to do the shaftwall, then frame the other wall....rinse, wash, repeat for the next level,......after dealing with a bunch of morons who framed the last apartment building I did in canton, I like to keep it as simple as possible

 

[Yankee Chronicler]

UL Design U305 is only the wall assembly. And it's a single row of 2x4 studs, not a double stud partition.

What Mark's detail shows isn't a UL Design U305, and it isn't continuous from the foundation to the roof. It's interrupted at each floor.

 

[Yankee Chronicler]

,......after dealing with a bunch of morons who framed the last apartment building I did in canton, I like to keep it as simple as possible

You are not keeping it simple -- you are making it far more complicated than it should be.

 

[hans@dha-architects.]

I fail to see how it's far more complicated

 

[Joe.B]

I fail to see how it's far more complicated

Don't mind him, his way or the highway kind of mentality, and he doesn't mean for his comments to sound as terse as they do.

 

[Yankee Chronicler]

I fail to see how it's far more complicated

It's more complicated because doing it your way means every hole cut in the sheetrock is a membrane penetration and must be closed with a listed penetration seal assembly. Electrical boxes, electrical cables, telecommunications and data cables, piping, etc. EVERY opening in the sheetrock will be a membrane penetration.

Plus, if it's built as shown in the section Mark posted -- the wall assembly isn't vertically continuous.

 

[hans@dha-architects.]

Don't mind him, his way or the highway kind of mentality, and he doesn't mean for his comments to sound as terse as they do.

sounds like it.....what may be easier for one contractor may be complicated for another

 

[steveray]

It's more complicated because doing it your way means every hole cut in the sheetrock is a membrane penetration and must be closed with a listed penetration seal assembly. Electrical boxes, electrical cables, telecommunications and data cables, piping, etc. EVERY opening in the sheetrock will be a membrane penetration.

Plus, if it's built as shown in the section Mark posted -- the wall assembly isn't vertically continuous.

Plumbing is not allowed in a common wall and an argument could be made that no penetrations other than electrical boxes are....

 

[hans@dha-architects.]

It's more complicated because doing it your way means every hole cut in the sheetrock is a membrane penetration and must be closed with a listed penetration seal assembly. Electrical boxes, electrical cables, telecommunications and data cables, piping, etc. EVERY opening in the sheetrock will be a membrane penetration.

Plus, if it's built as shown in the section Mark posted -- the wall assembly isn't vertically continuous.

I'm not building like the detail mark posted, my vertical wall assembly is continuous aside from the floor sheathing penetrating the membrane (if we find out that's not allowed, then maybe we'll switch to shaftwall unless the top mount hangers can't make the diaphragm work by themselves). Only penetrations in the membrane will be electrical, fiberglass junction boxes don't require putty pads in a rated assembly, I have no plumbing on the common walls

 

[Joe.B]

Plumbing is not allowed in a common wall and an argument could be made that no penetrations other than electrical boxes are....

Enter the "wet wall".

 

[Yankee Chronicler]

I'm not building like the detail mark posted, my vertical wall assembly is continuous aside from the floor sheathing penetrating the membrane (if we find out that's not allowed, then maybe we'll switch to shaftwall unless the top mount hangers can't make the diaphragm work by themselves). Only penetrations in the membrane will be electrical, fiberglass junction boxes don't require putty pads in a rated assembly, I have no plumbing on the common walls

If the subfloor penetrates the wall, the wall is not vertically continuous.

That's not "my way or the highway," that's code.