# Thermal Barrier for insulation on Ceiling



## vegeta82 (Jul 19, 2021)

I have a unique request I am going back and forth with.  

The most relevant code section is. (2015 IRC)

R316.4 Thermal barrier. Unless otherwise allowed in Section
R316.5, foam plastic shall be separated from the interior
of a building by an *approved thermal barrier* of not less than
1/2-inch (12.7 mm) gypsum wallboard, 23/32-inch (18.2 mm)
wood structural panel *or a material that is tested in accordance
with and meets the acceptance criteria of both the Temperature
Transmission Fire Test and the Integrity Fire Test of
NFPA 275.*

Builder wants to install a skim coat of Spray Foam on the ceiling of a house from the attic side after gypsum board installed.  (likely 2" of Closed Cell Foam).    He then wants to install a blown in insulation over this foam to complete the system and get the proper R Value.  

His hope is that he will not have to install any further product to achieve the attic ignition/thermal barrier.  I believe he would need a thermal barrier because there will be storage space in the attic.  

I have read this morning at length about the concept of either fiberglass, cellulose, or mineral fiber insulation complying as a thermal barrier.  

 But i can find nothing that supports the idea that a blown insulation meets NFPA 275.  Practically speaking however with 6" plus  of Cellulose on top of the foam i can't see much risk of the Foam being a potential hazard.



Some of the more interesting items i found.  And these are both from Foam Advocates.  But even here nothing I see shows it meets NFPA 275.




			https://www.idi-insulation.com/wp-content/uploads/2015/10/SPF-Thermal-Barriers.pdf
		







						Fire Barrier
					

FOAM-TECH creates superior insulation and environmental control solutions by installing safe, cost-effective, and environmentally-friendly  polyurethane foams. We have the capabilities to spray and inject a variety of foam systems to achieve a high R-value while providing both effective vapor...



					www.foam-tech.com


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## Rick18071 (Jul 20, 2021)

I myself would not accept fiberglass insulation as a thermal barrier. I'm sure you been in attics where the insulation was moved for some reason exposing the ceiling drywall. If there was a fire you could be in court even if the fire didn't start in the attic.


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## steveray (Jul 20, 2021)

So....he is using unfaced fiberglass? And how or what is it being blown into?


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## vegeta82 (Jul 28, 2021)

steveray said:


> So....he is using unfaced fiberglass? And how or what is it being blown into?


The intent is to use blown in cellulose over a ceiling assembly..


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## vegeta82 (Jul 28, 2021)

Rick18071 said:


> I myself would not accept fiberglass insulation as a thermal barrier. I'm sure you been in attics where the insulation was moved for some reason exposing the ceiling drywall. If there was a fire you could be in court even if the fire didn't start in the attic.


I see your point.  However the thought a product or protection is removed hence it created a concern is literally true in most any scenario right.


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## steveray (Jul 29, 2021)

It will come down to whether or not the "attic" is considered "interior" or not...



vegeta82 said:


> foam plastic shall be separated from the interior
> of a building


Around here, typically not...


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## tmurray (Jul 29, 2021)

We've had this discussion and do not accept even non-combustible insulation as a thermal break. If it doesn't meet the standard, it doesn't meet the standard.


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## Rick18071 (Jul 29, 2021)

steveray said:


> It will come down to whether or not the "attic" is considered "interior" or not...
> 
> 
> Around here, typically not...


To me if it's "inside" it's interior.

IBC definition: 
INTERIOR SURFACES. Surfaces other than weather
exposed surfaces.

But then you have this

IBC 2603.4.1.6 Attics and crawl spaces. Within an attic or
crawl space where entry is made only for service of
utilities, foam plastic insulation shall be protected
against ignition by 11/2-inch-thick (38 mm) mineral
fiber insulation; 1/4-inch-thick (6.4 mm) wood structural
panel, particleboard or hardboard; 3/8-inch (9.5 mm)
gypsum wallboard, corrosion-resistant steel having a
base metal thickness of 0.016 inch (0.4 mm); 11/2-inch thick
(38 mm) self-supported spray-applied cellulose
insulation in attic spaces only or other approved material
installed in such a manner that the foam plastic
insulation is not exposed. The protective covering shall
be consistent with the requirements for the type of construction.


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## steveray (Jul 30, 2021)

Or just look here:

R316.5.3 Attics. The thermal barrier specified in Section
R316.4 is not required where all of the following apply:
1. Attic access is required by Section R807.1.
2. The space is entered only for purposes of repairs or
maintenance.
3. The foam plastic insulation has been tested in accordance
with Section R316.6 or the foam plastic insulation
is protected against ignition using one of the
following ignition barrier materials:
3.1. 11/2-inch-thick (38 mm) mineral fiber insulation.
3.2. 1/4-inch-thick (6.4 mm) wood structural panels.
3.3. 3/8-inch (9.5 mm) particleboard.
3.4. 1/4-inch (6.4 mm) hardboard.
3.5. 3/8-inch (9.5 mm) gypsum board.
3.6. Corrosion-resistant steel having a base metal
thickness of 0.016 inch (0.406 mm).
3.7. 11/2-inch-thick (38 mm) cellulose insulation;
or
3.8. 1/4-inch (6.4 mm) fiber-cement panel, soffit
or backer board.
The ignition barrier is not required where the foam
plastic insulation has been tested in accordance with Section
R316.6.


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## vegeta82 (Jul 30, 2021)

steveray said:


> Or just look here:
> 
> R316.5.3 Attics. The thermal barrier specified in Section
> R316.4 is not required where all of the following apply:
> ...



Well i wouldn't say the attic is "interior".  Non conditioned with limited provisions i associate with interior i.e. proper lighting, conditioned, etc.

At issue is item #2.  In that the attic has limited storage.  We have always viewed this in conflict with item 2 and therefore foams would have to comply with providing thermal barrier protections.    

If it was a simple ignition barrier clearly they would meet item 3.7 with 1.5" of cellulose insulation providing the ignition barrier protections.


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## vegeta82 (Jul 30, 2021)

tmurray said:


> We've had this discussion and do not accept even non-combustible insulation as a thermal break. If it doesn't meet the standard, it doesn't meet the standard.


I guess the question is that cellulose is approved as an ignition barrier if installed 1.5".  

So we know it adds protection value.  But the code is silent on its use as a thermal barrier if used at a greater depth.


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## vegeta82 (Jul 30, 2021)

Rick18071 said:


> To me if it's "inside" it's interior.
> 
> IBC definition:
> INTERIOR SURFACES. Surfaces other than weather
> ...


Perhaps i need to rethink the context of interior.  However I still think the crux of the issue is compliance with a termal barrier as this attic has storage space.


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## steveray (Jul 30, 2021)

Yep...#2 is a killer either way...I did some research a while back on ignition barriers and it is difficult to find anything conclusive...


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