Fire Stopping Requirements at Chimney Passages Through Building Floors
Why we need fire blocking & combustible clearances
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Chimney construction: fire stopping.
This article describes the basic requirement for fire stopping needed where building chimneys or flues pass through building floors.
Fire stopping is a measure taken to slow the spread of fire between building floors - an event that could occur at openings cut to permit a chimney to pass through from one floor to another.
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Fire stopping at Chimney Passage Through Building Floors
Sketches courtesy of Carson Dunlop. [Click to enlarge any image]
Due to the drying of lumber and movement in structures the chimney shaft must
remain free of any ties into the framing of the building. The space between the
shaft and the building is or can be sealed with "fire code" [fire-rated] sheetrock or metal
flashing if a fire stop is required between floors.
Chimneys that pass through several floor levels of a home may be
required to be fire stopped at each penetration. Typical fire stops are sheet metal
or fire code sheetrock.
's sketch shows fire stopping at the fire-clearance gap provided between the chimney and wood floor framing (above left) and fire stopping around a metal chimney as it passes through building floors (above right).
Other Common Examples of Indoor Fire Clearance Safety Hazards
We often find flue vent connectors routed too close to combustible wood framing or, as in our photo at left shows, too close to other combustible materials such as the foam insulation just a few inches above this flue pipe.
Many building fire safety codes specify that the fire clearance between a flue vent connector and combustibles needs to be that specified by the appliance manufacturer.
Indeed some modern heating appliances permit pretty close clearances, as little as a few inches.
In the absence of a manufacturer's specification, we want to see at least 18" between the flue and the nearest combustible surface.
The reason for Fire Clearances from Wood Materials
The reason that building codes specify a healthy distance between wood materials (or other combustibles) and flue vent connectors is not just that the heat from the flue will immediately set the wood on fire. Rather it is also that wood that has been heated over time, even to the relatively low temperature of 200 to 300F, will be chemically affected to become more readily combustible.
Details are at PYROLYSIS EXPLAINED - separate article
Readers of this article should also
see FIRE CLEARANCES for MASONRY CHIMNEYS
and FIRE CLEARANCES, METAL CHIMNEYS as well
as FIRE CLEARANCES, SINGLE WALL METAL FLUES & VENTS.
This article series on chimneys, chimney construction, and chimney safety provide detailed suggestions describing how to perform a thorough visual inspection of chimneys for safety and other defects. Chimney inspection methods and chimney repair methods are also discussed.
Continue reading at FIRE & SMOKE DAMPERS, AUTOMATIC or select a topic from the More Reading links shown below.
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FIRE STOPPING in BUILDINGS at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.
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- Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. (416) 964-9415 1-800-268-7070 email@example.com. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' provides:
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- The Home Reference Book, a reference & inspection report product for building owners & inspectors.
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- Eric Galow, Galow Homes, Lagrangeville, NY. Mr. Galow can be reached by email: firstname.lastname@example.org or by telephone: 914-474-6613. Mr. Galow specializes in residential construction including both new homes and repairs, renovations, and additions.
- Mark Cramer Inspection Services Mark Cramer, Tampa Florida, Mr. Cramer is a past president of ASHI, the American Society of Home Inspectors and is a Florida home inspector and home inspection educator. Contact Mark Cramer at: 727-595-4211 mark@BestTampaInspector.com 11/06
- Roger Hankey is principal of Hankey and Brown home inspectors, Eden Prairie, MN. Mr. Hankey is a past chairman of the ASHI Standards Committee. Mr. Hankey has served in other ASHI professional and leadership roles. Contact Roger Hankey at: 952 829-0044 - email@example.com. Mr. Hankey is a frequent contributor to InspectAPedia.com.
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Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
- The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
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