FIRE STOPPING at CHIMNEY PASSAGES - CONTENTS: What are the Fire stopping or fire-block details needed where a chimney passes through building floors? Why we need fire blocking & combustible clearances. Chimney inspection, diagnosis, and repair
Fire stopping at Chimney Passage Through Building Floors
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.
Carson Dunlop Associates [at REVIEWERS] 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). Sketches here were provided courtesy of Carson Dunlop. [Click to enlarge any image]
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.
Fire Stopping where Chimneys Pass Through Closets, Walls, Floors
Where a metal chimney passes through building walls or floors fire blocking or use of a fire-blocking foam insulation may be required by local building codes.
At left you can see the orange fire-block foam spray insulation that oozed out from the partition wall that was sealed with this material. The building inspector also required us to trim away the excess foam.
NHFireBear, a frequent contributor to InspectApedia commented:
Ideally, there should be no unsealed openings from your closet to the attic, since any fire in the closet would naturally convect into the attic, possibly spreading the fire in an area where there are not smoke alarms or heat detectors.
That would create a life-threatening hazard to anyone in the building, if that were to happen. The ceiling should have a pass-through "ceiling mount" thimble/support, listed for the purpose (connector below, chimney above), and the chimney pipe through the roof should have shielding around it (metal hardware cloth, solid metal or solid wood), where it passes through the attic, to prevent combustibles from coming into direct contact with it.
A chimney fire should preferably stay in the chimney (even at 1,500 degrees) at least long enough to get the fire department there to save the roof.
Combustion air may be drawn into the burner either from a louvered closet door or from a properly installed air pipe from the outside or the attic, terminating in the burner or within a foot of the closet floor. Some local jurisdictions do allow gas-fired burners to have an unsealed overhead vent OUT to the attic.
NFPA 54 (2009): FIGURE A.126.96.36.199(1)(a).
I would prefer not to have that hazard for the citizens and firefighters in my town. The same is not allowed for OIL-fired burners.
NFPA 31 (2011): 188.8.131.52.
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 closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.
Try the search box below or CONTACT US by email if you cannot find the answer you need at InspectApedia.
(Feb 1, 2013) Doug G. said:
Thank you for writing about this... Please elaborate further on the details of the sentence "The chemical change of pyrolysis lowers the temperature at which a substance will catch fire." Please describe or document a research source that describes the details of the chemical change and subsequent lowered ignition temperature. I believe your statement to be correct, at least largely so, but I am able to find only small amounts of peer reviewed data that supports the statement. I am trying to understand the details of the process so I feel comfortable in explaining it to others. My current understanding is similar to what you have written but the "show me" people in my audience are (and rightly so!) asking "what are the chemical changes and how can the wood possibly ignite at a lower temperature?"
Use the "Click to Show or Hide FAQs" link just above to see recently-posted questions, comments, replies, try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.
Eric Galow, Galow Homes, Lagrangeville, NY. Mr. Galow can be reached by email: email@example.com or by telephone: 914-474-6613. Mr. Galow specializes in residential construction including both new homes and repairs, renovations, and additions.
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 - firstname.lastname@example.org. Mr. Hankey is a frequent contributor to InspectAPedia.com.
Arlene Puentes, an ASHI member and a licensed home inspector in Kingston, NY, and has served on ASHI national committees as well as HVASHI Chapter President. Ms. Puentes can be contacted at email@example.com
Wikipedia provided background information about some topics discussed at this website provided this citation is also found in the same article along with a " retrieved on" date. NOTE: because Wikipedia entries are fluid and can be amended in real time, we cite the retrieval date of Wikipedia citations and we do not assert that the information found there is necessarily authoritative.
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. Tel: (416) 964-9415 1-800-268-7070 Email: firstname.lastname@example.org. 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 extensive home inspection education and report writing material.
The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors. Special Offer: For a 5% discount on any number of copies of the Illustrated Home purchased as a single order Enter INSPECTAILL in the order payment page "Promo/Redemption" space.
TECHNICAL REFERENCE GUIDE to manufacturer's model and serial number information for heating and cooling equipment, useful for determining the age of heating boilers, furnaces, water heaters is provided by Carson Dunlop, Associates, Toronto - Carson Dunlop Weldon & Associates Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page "Promo/Redemption" space.
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.
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on these courses: Enter INSPECTAHITP in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
The Horizon Software System manages business operations,scheduling, & inspection report writing using Carson Dunlop's knowledge base & color images. The Horizon system runs on always-available cloud-based software for office computers, laptops, tablets, iPad, Android, & other smartphones