Stepped Chimney Span

[nwagner]

I encountered this chimney span in an attic yesterday. As you can see in the picture, the mortar joints are very sloppy and contain gaps. Stating the obvious, I found this chimney lacks a flue liner from the roof top and from seeing straight through the mortar gaps with my flashlight. The chimney is composed of concrete block in the basement and along the entire roof protrusion span and it serves a boiler heater.

[Shawn Rowe]

I see this type of corbeling on a lot of the older homes I do. I bet that wall isn't 12" thick and I bet that the projection is more than 1/2 the wall thickness. ..... probably would not meet current NFPA standards.

[nwagner]

Are there guidelines for acceptable chimney corbeling when everything else is in order, such as tight mortar joints and a functional flue liner?