Firestop spacing

**Mike Birenbaum** · 03-21-2011, 08:03 AM

Is there a acceptable spacing (gap) allowed at the fire stop inside the attic? I came across this installation the other day and just thought (as I inspected) if there was a fire in the flue / chimney area it would likely pass through this gap into the attic...Any thoughts are greatly appreciated.

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**Bob Harper** · 03-21-2011, 08:15 AM

If this is the listed component for this chimney system and has not been modified then it is listed and therefore acceptable. The Home Inspector should not worry themselves with measuring the gauge of components but rather the suitability of application. If the listing sticker on this firestop/ spacer was for another pipe for instance, then you should call it out.

What is more apparent is the lack of an attic insulation shield and the application of this component on the underside of the ceiling joists rather than on top of them.

These assemblies carry the misnomer of 'firestop'. They are really intended more as lateral spacers to ensure adequate clearance to combustibles and support. They have this gap BY DESIGN. Without this gap, you can raise chase temps. and raise chimney temps. Caulking such joints can be a fire hazard.

HTH,

**Marc M** · 12-21-2011, 10:33 PM

There has to be a point that is too big (gap) between the flue and fire stop spacer?

Chuck Kaatz · 12-22-2011, 12:11 PM

I recently sealed the opening around my B vent with high temp caulk.
There was condensation problems on the drywall near the opening.

R302.11 Fireblocking.
In combustible construction, 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.

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. The material filling this annular space shall not be required to meet the ASTM E 136 requirements.

**Marc M** · 12-22-2011, 03:32 PM

Okay, so Bob said not to worry (kind) and he's one of the foremost experts...

**Bob Harper** · 12-23-2011, 11:22 AM

Just make sure it is the correcte firestop. Compare the listing sticker on the pipe with the listing sticker on the firestop. Also, look for tool marks where the installer may have enlarged the opening with tin snips, which would void the warranty and listing and constitute a fire hazard.

**Jerry McCarthy** · 12-23-2011, 04:54 PM

Bob
If there's an opening in a firestop it can't be an effective firestop. What am I missing here?

**Marc M** · 12-24-2011, 12:21 AM

Underline is mine..

UL127
7.3.2 A firestop shall provide complete firestopping when the assembly is installed in a framed joist opening that is 1/2 inch (12.7 mm) greater on each side than the opening for which the assembly is intended. A spacer shall provide for continuous interference around the perimeter of the construction for a height of not less than 1 inch (25 mm). The inside diameter of the firestop opening shall not be more than 1/8 inch (3.2 mm) greater than the outside diameter of the chimney pipe, including chimney joints and raised projections.

**Bob Harper** · 12-24-2011, 11:36 AM

If you measure the circumference at the widest point, usually the female down outer casing then add 1/8" diameter gives you the maximum diameter. Now, if the firestop is listed for use with that system and there is no indication it has been tampered with then walk away. FYI, you cannot caulk firestops on factory built fireplaces. Trapping that heated air in the chase can lead to fires--trust me. UL agrees with this position btw. Those chases need to breathe, which is why the chase tops often are specified with a ventilated gap where the top sits on the framing.

Firestop is a bit of a misnomer--it is really more of a lateral support/ spacer. You can caulk unlisted firestops such as site fabricated ones around plumbing stacks, etc. but not listed fireplaces. You can caulk most gas direct vents but read the listed instructions or get it in writing from the mfr.