Vent Clearance and Fireblocking

[inspectorwill]

In disagreement with builder on vent clearance and fireblocking in this two story home. The Noritz tankless water heater vent pipe label calls for 1" clearance to combustible material. No clearance is provided between the vent and drywall where it passes through the ceiling. Builder insists no clearance is required because "Type X" drywall was used at garage ceiling. I have never seen any allowances for drywall contact when Type X is used. Additionally, there is no blocking where the furnace and water heater vent chase (shared) intersects the attic floor. Again the builder insists the attic floor does not require blocking because the garage ceiling is Type X and sealed at the bottom of the chase. I understand Type X to be more fire resistant than standard drywall but still combustible. I have never seen an exclusion for not sealing the chase at the attic floor. I call BS on both unless anyone can correct me.

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[Robert Jones]

I haven't read an exception to the fire blocking rule either. I would think that the manufacturer install instructions would be the proof the builder needs. Some are stubborn and you can imagine how many homes he has built like this.

Found this in the California Building Code:

FIRE BLOCKS

Fire blocking is required in all stud walls at ceilings and floor levels. The vertical distance between blocking shall

not exceed ten feet. It is also required where a ceiling is below the top plate of the wall such as soffit ceilings,

and around the edges of tubs and showers on wood floors. Holes for pipes that pass from one floor level to

another or into an attic space must have the openings firestopped with non-combustible material. Where

insulation batts are used as fireblocking between studs, they must be stapled in place.

Fire blocks must be a minimum of 2X nominal thickness or 23/32 plywood with joints backed with 23/32

plywood, or gypsum board, mineral wool, or other non-combustible material securely fastened in place.

[Bill Kibbel]

Type X drywall is not non-combustible. It has no fire rating by itself. The fire rating is when it is used as a fire-resistant system. There is no exclusion for the required clearance from an appliance vent.

It wouldn't matter if the garage was lined with asbestos sheets. There is no exception. A fire could spread through that chase.

[inspectorwill]

Thanks guys.