AskCodeMan

Hey Jerry, I have a question regarding DWV within a common wall separating a townhouse / two adjoining units. If there are plastic dwv within this wall, how can it be effectively sealed when its plastic and two, per the exception below in bold; what is the "or what". Meaning, what is the fix if there is dwv within this wall? Hopefully I explained this well enough..

R302.2 Townhouses. Each townhouse shall be considered a
separate building and shall be separated by fire-resistancerated
wall assemblies meeting the requirements of Section
R302.1 for exterior walls.
Exception: A common 1-hour fire-resistance-rated wall
assembly tested in accordance with ASTM E 119 or UL
263 is permitted for townhouses if such walls do not contain
plumbing or mechanical equipment, ducts or vents in
the cavity of the common wall. The wall shall be rated for
fire exposure from both sides and shall extend to and be
tight against exterior walls and the underside of the roof
sheathing. etc...

Marc,

I have a question regarding DWV within a common wall separating a townhouse / two adjoining units. If there are plastic dwv within this wall, how can it be effectively sealed when its plastic ...

Firestopping collars are available which are wrapped around the PVC and secured to the rated wall or ceiling. The metal collars contain a thick intumescent pad which wraps around the outside of the PVC between the PVC and the metal collar. When there is a fire, as the PVC softens the intumescent material expands, being as the intumescent material is contained within its metal collar it expands into the space left by the collapsing PVC. Essentially, the intumescent material seals off what was the open space inside the PVC.

and two, per the exception below in bold; what is the "or what".

The wall between townhouses are required to be 2 hour rated walls. The two hour rated walls can have plumbing, mechanical, electrical, etc. within the walls provided the items are firestopped with an approved design firestopping system (device) where the item(s) penetrate into or through the 2 hour rated wall.

The exception says that the wall only needs to be a 1 hour rated wall if there is no plumbing, mechanical, electrical, etc., in the wall.

Meaning, what is the fix if there is dwv within this wall?

There is more than just the DWV to be concerned about in that wall: the truss goes through that wall and each townhouse is supposed to be constructed such that if the townhouse next to it burns down the other townhouse remains standing - if that trusses does what it looks like it does then both townhouses will come down when either one comes down; there are unsealed penetrations into that wall from the said you took the photo from and most likely there are similar penetrations from the other side.

Can the wall be sealed? If that is a two hour rated wall, it can be sealed, but at great expense. If that is a one hour rated wall it can be made into a 2 hour rated wall at even greater expense. If the trusses do as it looks like they do, that can also be corrected ... at an even greater expense (truss engineer would need to review the design, design a modification for the trusses, then the modification done, which basically means removing the drywall from both sides of that wall to make the repairs.

Of concern is what is that wall like below the ceiling, and is the rest of the structure constructed too allow one townhouse to remain standing if the other burns down? Probably not.

I was hoping you weren't going to confirm what I suspected. It this image consistent with what you are describing?

Basically, yes.

There could also be one common wall constructed as a 2 hr rated wall, with proper firestopping (versus fireblocking) for each item in that wall.

Of course, trying to construct a single common wall which will remain standing when the structure on one side falls is a bit difficult (unless the common wall is either CMU or poured concrete).

All clear now, thanks much Jerry.