Thread: Fireblocking material

Attic in a 2-year old house. I see no fireblocking around the vent for the manufactured wood fireplace in living room. In addition, what is not clearly visible in the pictures is that fiberglass batting has been used to fill the space between the upper section of studs of the vertical wall at one side of the chase.

Question: I see the word 'fireblocking' thrown about all the time, but maybe I am not clear on what is defined as a proper fireblock. From 2006-IRC (which would have been in force at time of construction), I see this:

R602.8 Fireblocking required. Fireblocking shall be provided to cut off all concealed draft openings (both vertical and horizontal) and to form an effective fIre barrier between stories, and between a top story and the roof space. Fireblocking shall be provided in wood-frame construction in the following locations.

1. In concealed spaces of stud walls and partitions, including furred spaces and parallel rows of studs or staggered studs; as follows:

1.1. Vertically at the ceiling and floor levels.

1.2. Horizontally at intervals not exceeding 10 feet.

4. At openings around vents, pipes, ducts, cables and wires at ceiling and floor level, with an approved material to resist the free passage of flame and products of combustion.

5. For the fireblocking of chimneys and fireplaces, see Section R1003.19.

R602.8.1 Materials. Except as provided in Section R602.8, Item 4, fireblocking shall consist of ……

Batts or blankets of mineral wool or glass fiber or other approved materials installed in such a manner as to be securely retained in place shall be permitted as an acceptable fire block. Batts or blankets of mineral or glass fiber or other approved nonrigid materials shall be permitted for compliance with the 10 foot horizontal fireblocking in walls constructed using parallel rows of studs or staggered studs.

RI003.19 Chimney fireblocking. All spaces between chimneys and floors and ceilings through which chimneys pass shall be fireblocked with noncombustible material securely fastened in place. The fireblocking of spaces between chimneys and wood joists, beams or headers shall be self-supporting or be placed on strips of metal or metal lath laid across the spaces between combustible material and the chimney.


My question. What would be required to provide proper fireblocking around this exhaust vent?

Terry B

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Originally Posted by Terry Beck

My question. What would be required to provide proper fireblocking around this exhaust vent?

The manufacturer of that chimney makes a listed fireblock piece made of metal, probably 16 gage sheet metal, which needs to be used as combustible fireblocking is not allowed to be within the clearances stated (typically 1" to 2") of the chimney.

EC Jerry means like this, but oops, no cigar................

I think I understand how it should have been done (see attached pics). The illustrations in the manufacturer's manual is part of why this item was in my report.

If I understand it correctly, then it is ok to use fiberglass batting as one of the walls in the chase that surrounds the vent. Right?

Part of my question then, is how to rectify this situation (I know that is not my job, but still . . . ).
Given the statement in IRC

"Batts or blankets of mineral wool or glass fiber or other approved materials installed in such a manner as to be securely retained in place shall be permitted as an acceptable fire block."

I can certainly conceive that some builder will read this section of the code and then try to use fiberglass batting as the firebreak material around the vent across the opening in the floor of the attic, as long as it is 'securely retained'. (Of course, then there is the other issue about insulation blocking, and 2" clearance to the insulation).

and, yes, the manufacturer does list a "ceiling firestop" (two sizes available) as one of the optional components for the chimney assembly.

Originally Posted by Terry Beck

If I understand it correctly, then it is ok to use fiberglass batting as one of the walls in the chase that surrounds the vent. Right?

On one (or more) of the walls of the chase, as long as the insulation maintains minimum clearance to combustible material (which includes maintaining that same minimum clearance to insulation)

Given the statement in IRC

"Batts or blankets of mineral wool or glass fiber or other approved materials installed in such a manner as to be securely retained in place shall be permitted as an acceptable fire block."

Not all fireblocking material is created equal, nor are all fireblocking materials allowed to be used in all locations and conditions.

I can certainly conceive that some builder will read this section of the code and then try to use fiberglass batting as the firebreak material around the vent across the opening in the floor of the attic, as long as it is 'securely retained'.

Not allowed, as stated above, not all fireblocking material is created equal nor allowed to be used for all uses, which is why ...

(Of course, then there is the other issue about insulation blocking, and 2" clearance to the insulation).

... you are correct in that the insulation needs to maintain that clearance, which means that the insulation is not allowed to be used as fireblocking *in that location for that purpose*.