Using abandoned chimney as plumbing chase for vent?

[EIR]

I can't find a definitive answer.

Can one use an abandoned (zero other appliances be it gas, wood, etc) cinder block chimney with Terra Cotta flu as a chase for a PVC vent for a drain?

If so, can the vent merely stick out past the top of the chimney masonry but inside the existing vented rain cap (supported of course) or should I remove the existing mesh rain cap, install pipe than cap the top of the chimney with metal around the pipe?

I am attaching an example picture of what is currently on the roof.

 

[FullySprinklered]

I vote yes. Looks like a piece of luck to me.

 

[Sponsor]

 

[Kreemoweet]

How would the required pipe supports be installed? It's hard to imagine any inspector
finding such a thing acceptable.

 

[EIR]

It's a single story home. From where it goes into the base of the chimney inside the mechanical room to where it exits the top is roughly 7ft. Can support it at the top numerous ways (coupling glued on over the pipe penetrating a piece of metal or plywood, split ring clamp attached to to threaded rod, metal pipe band wrapped around and tacked with some of those red head masonry pins.

At the bottom the hole in the block would support it or I could cantilever a piece of wood or unistrut to catch it.

Obviously i would use some metal sheet and a duct mastic caulk to seal the metal to the chimney and the hole cut around the pipe on the lower portion much like they used to do with gas flues.

I know abandoned chimneys like I describe can be used as wire chases.

Since it is no longer venting gas or wood burning appliances it's essentially a masonry wall cavity open to atmosphere at the top.

If not I'll use an aav next to the utility sink above the flood rim and call it a day. There is no where to side wall vent it to meet code. Going through the cathedral ceiling and through roof is not desired or feasible at this point. The room for all intents and purposes is only accessible from the outdoors. It used to contain an old gas forced air unit and water heater. It is outside the air barrier and thermal envelope of the main house. It's a tiny attached garage.


The sink will be draining into an already vented system and an aav is legal where I am.


No where am I suggesting I dump the vent into the chimney and call it a day.

 

[Dana]

Legal or not it's better overall to just demo out the chimney, and re-use the chimney chase, not the chimney itself. Chimney chases are notoriously poorly air sealed and a major driver of outdoor air infiltration, and common water leak point. If you can, just get rid of it.

With the chimney gone it's very easy to fix those issues, air-sealing the plumbing stack penetration at the attic floor (and basement ceiling, if it runs all the way down to a basement), and adding robust waterproofing at the roof penetration. If the chimney is left in place the air sealing is more complicated, since both the penetration for the plumbing stack into the chimney and the chimney to the chimney chase need to be air sealed to fix the stack effect infiltration drives.

 

[EIR]

I can't get rid of it at the moment. Roof has another good 10 years on it. Previous owners had it done not long before I bought it. If I rip the chimney out I'd have to patch the hole. (Sheathing, paper, shingles).


There are no left over shingles by the previous owner so I'd have to have it patched with a close but not perfect match.

The chimney has no chase. The mechanical room is an un heated space off the back of the home on grade. The home is on a crawl.

I'm looking at the block....No chase around the chimney. Inside I can see the terracotta flue.

I didn't want to put another roof penetration if I could avoid it. When I do reroof I'm going standing seam metal I think and like to minimize roof penetrations. When the chimney is removed in the future I will have a path to get the vent up into the attic and tie it in with the 4" vent stack.

I always prefer to vent to atmosphere vs using an aav.

This utility sink was a bit of an afterthought in full disclosure.

Sounds like I'll aav it until I can remove the chimney in the future.

Once again to be clear...This space is totally outside the home's thermal envelope. It's outside the air barrier. It does share vented attic space with the main attic.