Can Fiberglass Insulation Burn?

By
Home Inspector with Jay Markanich Real Estate Inspections, LLC

I know, it's the age-old question:  can fiberglass insulation burn?

Not really, but there is a caution! 

There are many kinds of chimney vents - masonry and metal. 

One particular type is called a "Type B vent."  A Type B vent utilizes two different tubes - an interior tube which carries the heat and a surrounding tube which does not touch the interior tube. 

The separation allows for the dissipation of heat so that what outer ring touches would not get too warm.

It is a safety feature.  This Type B vent is used for gas appliances (furnaces and fireplaces), not solid-fuel appliances like wood or coal.

However, the International Residency Code requires a separation between the outer ring and anything it might touch inside a house.

Why?  If the outer ring is cooler what could be the harm of it touching anything?  And especially something that is not considered combustible, like fiberglass insulation?

From the IRC:

G2425.4 Insulation Shield.

Where vents pass through insulated assemblies, an insulation shield constructed of not less than 26 gage sheet metal shall be installed to provide clearance between the vent and the insulation material.  The clearance shall not be less than the clearance to combustibles specified by the manufacturer's installation instructions.  Where vents pass through attic space, the shield shall terminate not less than 2 inches above the insulation materials and shall be secured in place to prevent displacement.

Most manufacturers require a 1" or 2" space around their Type B vent materials.  Often the space instruction is stamped onto the vent itself.  In this case I could see no stamp, so on a report I can only say that the manufacturer should be consulted as to the distance they require.

But the question remains - if fiberglass insulation cannot burn, why worry?  Keep in mind, this is not only a code, it is a FIRE code.  Fire codes are very specific.

The answer to the question is:  because of the rare, but possible, chimney fire.  Chimney fires can burn around 2,000F!  That's hot!  At that temperature fiberglass insulation actually acts to absorb and spread the heat.  Hence, nearby combustible materials, as you see here, can ignite.  This is a condo.  A spreading fire would not be good.

This inspection is on a new condo, before anyone has occupied it.  The fabled final walk through!  I often wonder how the builder will react to a comment on a report about something like this, perhaps considering it to be unimportant minutia.  The builder might even try to skirt it by saying the county already approved it.  This is in a very narrow attic space requiring a taller-than-usual ladder to get to (10').  So, did the county see it?  The home inspector sure did!  I wonder what the local fire marshal would say!

Nonetheless, I don't write the code.  And the code is a MINIMUM standard!  Building to code is NOT impressive.  Building to a Best Practices standard would be impressive!

My recommendation:  it is not the requirement of the home inspector to cite codes.  But sometimes it's necessary.  Either this insulation installer did not know about the Type B vent separation instruction, or did not care.  I suspect the former.  But it's the home inspector's job to observe and report.  Even if the code is not cited in the report (which this home inspector did) it is still the code.  If the supervisor does not know that, well, shame on him...

And yes, I was the home inspector.

 

 

 

Posted by

Jay Markanich Real Estate Inspections, LLC  

Based in Bristow, serving all of Northern Virginia.

Office (703) 330-6388   Cell (703) 585-7560

www.jaymarinspect.com


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  1. Chris Smith 09/19/2013 10:58 AM
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Show All Comments
Rainmaker
692,536
Clint Mckie
Desert Sun Home, commercial Inspections - Carlsbad, NM
Desert Sun Home, Comm. Inspection 1-575-706-5586

Hi Jay,

I have taken pictures and wrote this up for years. Nothing is ever done about it. But I will continue as a SOP.

I have rarely seen any damming of the insulation no matter what kind or how it was installed.

Have a great day in Bristow.

Best, Clint McKie

Sep 19, 2013 08:56 AM #25
Rainmaker
1,233,173
Jay Markanich
Jay Markanich Real Estate Inspections, LLC - Bristow, VA
Home Inspector - servicing all Northern Virginia

I'm glad you do Jill!  Stop by anytime!

Mike - I have never known a county inspector to venture into the attic for a final inspection.

Bill - most people would not be.  This has been a problem for a long time however!

Juan - not sure why there would be debate!  There is the code and there is the manufacturer's instructions.  Either trumps the issue and set the course.

Sep 19, 2013 09:39 AM #26
Rainmaker
1,233,173
Jay Markanich
Jay Markanich Real Estate Inspections, LLC - Bristow, VA
Home Inspector - servicing all Northern Virginia

Suzanne - inspectors are looking at a thousand things during a home inspection!

It does Rich.  They have those instructions for reasons.

Dwight - in this case the space is very narrow and lots of insulation!  But summer temps don't stop me from poking around!

Not sure what will be done here Clint, but as you know, we have the obligation to observe and report.

Sep 19, 2013 09:41 AM #27
Rainmaker
567,615
Chris Smith
Re/Max Chay Realty Inc., Brokerage - New Tecumseth, ON
South Simcoe, Caledon, King, Orangeville Real Esta

Jay, this I did not know.  I, too, would rather aspire to Best Practices than Code, which tend to be minimums...

Sep 19, 2013 11:10 AM #28
Rainer
277,179
Steven Cook
No Longer Processing Mortgages. - Tacoma, WA
- Pierce, King, Kitsap, Thurston, Mason Counties

Jay -- as has been noted before, on multiple builds like this (whether condos, or plat of homes) the builder is usually consistent on their error/omissions like you found here -- it will be interesting to know if he fixes them all or just this one.

Sep 19, 2013 11:10 AM #29
Rainmaker
1,233,173
Jay Markanich
Jay Markanich Real Estate Inspections, LLC - Bristow, VA
Home Inspector - servicing all Northern Virginia

The code is the floor of expectation Chris.  Best Practice is something entirely different.  That is what inspired me to start the Best Practices Group here on AR.

Steven - I expect the same mistake is made EVERYWHERE in this development because it is probably the same insulation company throughout.  The builder has no incentive to fix anything but what it has been caught on.

Sep 19, 2013 11:16 AM #30
Rainmaker
158,299
Trisha Bush
Preferred Properties Land & Homes - Walla Walla, WA
Broker ~ Owner

Great information to know. I wasn't aware of this. You'er completely right about not doing things to the minimum level. Always strive for the best. But if you're not going to strive for the best, AT LEAST be up to code.

Sep 19, 2013 11:50 AM #31
Rainmaker
1,233,173
Jay Markanich
Jay Markanich Real Estate Inspections, LLC - Bristow, VA
Home Inspector - servicing all Northern Virginia

Thanks Trisha.  They are SUPPOSED to be up to code!  Best Practices are voluntary!

Sep 19, 2013 11:54 AM #32
Rainmaker
302,065
AJ Heidmann
McEnearney Associates, Inc. - Alexandria, VA
YOUR Alexandria & Arlington, VA Real Estate Expert

Jay - Great information as usual... and I had never though of the fiberglass carrying the heat over to other combustible material.

Sep 19, 2013 01:32 PM #33
Rainmaker
1,233,173
Jay Markanich
Jay Markanich Real Estate Inspections, LLC - Bristow, VA
Home Inspector - servicing all Northern Virginia

AJ - when it gets below 10F fiberglass insulation actually draws heat out of the house!

Sep 19, 2013 01:55 PM #34
Ambassador
1,491,628
Michael Thornton
Complete Home Inspections, Inc. - Brentwood, TN
Home Inspector - Nashville, TN area - 615.661.0297

Good evening, Jay. AT 2,000 degrees, the metal tubing would melt or warp. Whether insulation was present or not, the property would most likely be toast!

Sep 19, 2013 04:49 PM #35
Rainmaker
1,233,173
Jay Markanich
Jay Markanich Real Estate Inspections, LLC - Bristow, VA
Home Inspector - servicing all Northern Virginia

I don't know if it would melt Michael, but that is the temp the code is intended to try to control - the 26 gage is important.   Confined fires get hot!

Sep 19, 2013 05:59 PM #36
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Judi K Barrett
Judi Barrett~Integrity Real Estate Services~Idabel, Oklahoma - Idabel, OK
Broker/Owner, Integrity Real Estate Services -IDAB
I looked at a home this morning where the owner had installed cellulose completely covering the vent/heater/light in the bathroom...
Sep 19, 2013 08:08 PM #37
Rainmaker
1,488,066
Laura Cerrano
Feng Shui Manhattan Long Island - Locust Valley, NY
Authentic Feng Shui Expert

I've heard about the metal issues. Thanks for the reminder. :)

 

Love and light,

Laura

Sep 19, 2013 09:10 PM #38
Rainmaker
1,233,173
Jay Markanich
Jay Markanich Real Estate Inspections, LLC - Bristow, VA
Home Inspector - servicing all Northern Virginia

That's pretty cool to see you go in the attic Judi!  It's good for the psyche!  That kind of combo appliance probably does not have an IC sticker (Insulation Compatible) which would allow insulation to be packed around and over it.

Metal is good Laura!  Especially when treated right.

Sep 20, 2013 04:13 AM #39
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Charles Buell
Charles Buell Inspections Inc. - Seattle, WA
Seattle Home Inspector

Jay, I see these missing baffles all the time.  People just don't get that the pipe will not be able to cool itself properly and in some cases the insulation can conduct that heat to materials that do burn.

Sep 20, 2013 06:39 PM #40
Rainmaker
1,233,173
Jay Markanich
Jay Markanich Real Estate Inspections, LLC - Bristow, VA
Home Inspector - servicing all Northern Virginia

That's pretty much what the fire code reads around here Charlie.  And that on top of a stud wall a solid fire block needs to be installed to prevent fire from passing and spreading via insulation also.

Sep 21, 2013 02:43 AM #41
Rainmaker
366,024
Donald Hester
NCW Home Inspections, LLC - Wenatchee, WA
NCW Home Inspections, LLC

Jay, what is a B vent ; ) Anyway you are right they must be installed correctly.

Sep 23, 2013 06:17 PM #42
Rainmaker
1,233,173
Jay Markanich
Jay Markanich Real Estate Inspections, LLC - Bristow, VA
Home Inspector - servicing all Northern Virginia

I think there's A, B and C, Don.  Kind of like the Sears system - good, better and best.

Yeah, that's it.

Sep 24, 2013 12:29 AM #43
Rainer
72,287
John J. Woods
Aardvark Appraisals - Palm Desert, CA

 

   No challenge to your work, or the code, but I'm just curious:  Have you ever heard of a chimney fire in a gas-fired appliance vent that was never used for solid fuel?

 

Sep 29, 2013 07:29 AM #44
Show All Comments
Rainmaker
1,233,173

Jay Markanich

Home Inspector - servicing all Northern Virginia
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