Does Your Spray Foam Insulation Need a Thermal or Ignition Barrier?

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Closed cell spray foam insulation in an attic without an ignition barrier

To say spray foam insulation has become popular in green building over the past decade is like saying Peyton Manning is a good quarterback. It's an understatement. Although it's certainly not used in every green building project, it's become one of the most popular ways to build an air-tight house. In the early days, building codes hadn't caught up with how best to use this material, but that's changing. Change begets confusion, though, and the requirements for thermal and ignition barriers are one area where there's a lot of that.

Do you need a thermal barrier?

Yes, absolutely. If you put spray foam insulation in a building, it needs a thermal barrier. That's what separates it from the occupied spaces. If there's a fire in the building, a thermal barrier keeps the combustible spray foam from the flames to increase fire resistance. The International Residential Code (IRC) and Internation Building Code (IBC) both include requirements for thermal barriers (and ignition barriers, too; see below).

The standard prescriptive material that can be used as a thermal barrier is 1/2" gypsum board (a.k.a. drywall or sheetrock). Anything else has to be approved as an 'equivalent thermal barrier' by undergoing tests for temperature transmission and fire integrity. In some cases, however, you need only one test. According to the Spray Polyurethane Foam Alliance (SPFA), "Under specific conditions, the temperature transmission test can be waived if approved by building code authorities on the basis of large-scale fire testing representing actual uses." (See their pdf document, Thermal and Ignition Barriers For The SPF Industry.)

Do you need an ignition barrier?

This is where things get a little tricky. If a home has spray foam insulation in an attic or crawl space, the building code requires using materials or assemblies that offer some fire resistance but not as much as is required for a thermal barrier. If you've got spray foam insulation in an attic, for example, it's probably already separated from the living space by a thermal barrier. Most ceilings are made of 1/2" drywall. But the spray foam is still exposed to the attic and needs an ignition barrier.

In this case, you have a choice of several prescriptive materials approved by the code as ignition barriers:

  • 1.5" mineral fiber insulation
  • 1/4" wood
  • 3/8" particleboard
  • 1/4" hardboard
  • 3/8" drywall
  • 0.016" corrosion-reisistant steel

Again, other materials and assemblies may be allowed based on tests described by the Internation Code Council Evaluation Service in their Acceptance Criteria 377. The types of spray foam insulation that I'm aware of that qualify to be sprayed without an ignition barrier are:

When do you need an ignition barrier? According to the IRC and IBC, an attic or crawl space needs an ignition barrier over the spray foam if the space can be accessed but will not be used for storage or auxiliary living space. You don't need an ignition barrier if the space cannot be accessed without cutting into it, if it is not connected to other spaces, and if it does not communicate with other spaces.

Enforcement is spotty

At least in my part of the US (the Southeast), enforcement of this part of the building codes is spotty. Some jurisdictions are sticklers about it and some don't even know about it. The best policy, as always, is to find out what they require and what they'll accept. Then use your best judgement.

One thing to be aware of is that not everything claiming to be a thermal or ignition barrier actually meets the requirements. If it's not on your building department's approved list, ask the company selling it for their test data and evidence of code approvals. You may need them to satisfy your building inspector.

What if your local doesn't require anything? Well, it sure is tempting to keep your costs low and omit ignition barriers in attics and crawl spaces. But what if that house burns, and the insurance company refuses to pay because there was no ignition barrier? It doesn't take a genius to know who the homeowners are going to come after.

The bottom line is that if you're using spray foam insulation, you need to know the code about thermal and ignition barriers and use them where necessary. You need to know your materials, too, and what qualifies in each case.

 

Download Thermal and Ignition Barriers For The SPF Industry (pdf) from the Spray Polyurethane Foam Alliance. This document explains thermal and ignition barriers in more detail and gives the code references and testing requirements.

 

Related Articles

4 Pitfalls of Spray Foam Insulation

The #1 Question to Ask before Putting Spray Foam in Your Attic

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Comments

Armando

Demilec APX is an spray foam that you don't need to apply an ignition barrier in attics or crawl spaces.

Chris Maher

Great post. Do the ignition and thermal barrier requirements apply equally to .5 lb density spray foam, as well as 2.0 lb density spray foam? 
 
What about the high density foam insulation 2" board stock frequently used in crawlspaces attached to basements?

John Nicholas

I would point out the limitation of access to and communicating to other spaces has one exception. 
 
If there are ducts or control wires in the space, it needs the ignition barrier.

Allison Bailes

Armando: Thanks! I've updated the article. 
 
Chris M.: Yes, I meant to mention in the article that this applies to both open cell (a.k.a. low density or 1/2 pound SPF) and closed cell (a.k.a. medium density or 2 pound SPF). Foam board insulation also needs to meet the requirements for thermal and ignition barriers, and some products, like Dow Thermax, have gotten approval to be left exposed. 
 
John N.: Thanks for the clarification. 
 
Charles: That photo is closed-cell SPF, and it's not sprayed perfectly uniformly. As long as it has the minimum thickness required (3" on a ceiling here in the Atlanta area), it should be fine. I've discussed some problems with SPF installations in the articles listed in the Related Articles section above. This photo is from about 10 years ago, though, and has no ignition barrier.  

Gary Nash

I just skimmed the "Thermal & Ignition Barriers..." from the link above. Looks like this means that a roof assembly insulated with spray foam in an attic will also have to be enclosed with one of these barriers. So now you have the cost of the insulation + the cost of the barrier to sell the Owner on. 
 
Sprayed cellulose is listed as an alternative ignition barrier. Interesting. 
 
Is this going to throw the foam guys for a loop? Walls are enclosed anyway, but roof assemblies are not. Makes cellulose or SIPS panels look like the better alternative. 
 
Anybody else concerned about all of the flammable foam filling a structure? - whether it is enclosed or not.

Jim Smith

So the soy-based foam we had installed in 2012 did or did not need an ignition barrier ? The installer charged us an extra couple of hundred dollars for a sprayon coating for the foam that supposedly acts as an ignition barrier.

Allison Bailes

Gary N.: Yes, foam is a combustible material. So is wood, and we use a lot of it in houses, some of it in the living space without ignition barriers. I'm not trying to make light of the issue; just saying that foam gets a lot of attention, but fire safety is more than just choosing non-combustible materials.  
 
Martin H.: Thanks. I'll add it to the ones already mentioned in the article. 
 
Jim S.: That depends on where it was installed and whether the foam they used qualifies as meeting the fire resistance tests by itself. If they charged you for a coating, the foam probably didn't qualify by itself. 
 

Debbie

I'll give my scenerio with a question to Alison at the end. I'd really like your input, as home owners here get all kinds of stories from foam reps. 
 
in the south we use open cell foam @ the roofline. to meet code's requirement for cathedralized ceilings (as told by code inspector) for the unvented attic, we put 6-7" of open cell..filling rafter bay & faces of 2x's.not the partially filled install in above article which meet code somewhere?? anywhere?? 
the ignition barrier is the sheetrock of the ceiling to the livng space below. 
 
so is there a problem as you see it Alison with the install as described? 
 
second part of my comment: 
I've had concerns with foam in walls with only 2-3" and the resulting air space & convective currents. spray foam for walls is not one of my recommendations to my clients. instead foam sheathing to exterior of walls caulked,taped & sealed. conventional insulation & air tight drywall approach. a better and affordable wall with no extremely long payback like spray foam in walls. 
 
good posting Alison as always. thanks for providing such a great resource for pros & homeowners.

Sue Cameron

Is there a Stayflex thermal barrier coating we can use on foam board as a thermal coating rather than gypsum board?

David Johnson

Charles spoke of a "huge problem" of convection within cavities not filled with foam. This is a false assertion. The trillions of trapped air cells in foam insulation prevent heat transfer at a rate that would cause those problems. Also the wood framing members are relatively good insulators themselves unless the wood is particularly dense. Convection currents against foam insulation are not the problem he asserts. He also said" the homeowner is literally pissing money away if he pays for this spray foam job - or any job like it - for he will only be gaining a marginal amount of insulation effectiveness." This is a ludicrous statement. The structure pictured above will have a very effective performance despite his assertions. My only concern is humidity. Closed cell foam does not permit moisture migration and trapped moisture could be a problem, especially if the AC is not running due to moderate to cold temperatures.