Thermal Barriers, Ignition Barriers:
What’s the Difference?


By  Brandon O’Brien, Demilec (USA), LLC

Over the past few years, the Spray Polyurethane Foam Industry has made rapid advancements in the areas of technology, safety, advocacy and acceptance. Along with these advancements have come some changes with regards to how spray foam can provide alternatives to the prescriptive code requirements for ignition barriers. The most substantial recent change in the spray foam industry is the adoption of Appendix X in the AC-377, Acceptance Criteria for Spray Applied Polyurethane Foam. This change has brought about new large scale fire testing and special approval requirements related to omitting ignition barriers in attic and crawlspace applications. Whether an ignition barrier or thermal barrier is required depends greatly on the situation.

These new changes have brought about numerous questions regarding how spray foam insulation can be installed in structures. What is the difference between a thermal barrier and an ignition barrier? Do I need to install a thermal barrier or ignition barrier on all spray foam surfaces? What are the differences between the thermal barrier and ignition barrier substitute coatings currently popping up across the market? When is storage permissible in an attic or crawl space? The answers to these questions are often vague or filled with confusing terminology that leaves the foam applicators as well as the end customers more confused than ever. Let’s take a look and attempt to clear up some of the confusion surrounding these recent changes in the spray polyurethane foam world.

Thermal Barriers

First let’s look at thermal barriers. A thermal barrier is a material that separates the foam from the interior of the building and will slow the temperature increase as well as the spread of fire on that surface.  Currently, the building code defines a thermal barrier as ½” gypsum board or an equivalent 15-minute thermal barrier, complying with and installed according to the appropriate sections of the building code.  After a thermal barrier is installed, the interior space can be used for nearly any purpose.  It is important to remember that thermal barriers are only required for interior applications. If medium or high-density foam insulation is used on the exterior of a structure, it will not require a thermal or ignition barrier as they will typically meet an exception to the thermal barrier requirement. If you are spraying foam insulation into an attic, and you know that the space will not be used for storage, then you may want to consider using an ignition barrier.

Ignition Barriers

An ignition barrier is a lesser fire protection requirement than a thermal barrier for attics or crawlspaces in which entry is made ONLY to service utilities, which allows 3/8” gypsum wallboard or other code-approved barriers to ignition to be installed over the foam. It is very important to remember that when an ignition barrier is installed in an attic or crawlspace, it may not be used as a living space or for storage of any kind. If the attic will be used for storage or as an extra room in the future, then you must install a thermal barrier. An ignition barrier is unique in that it is an exception to the code requirement for thermal barriers and is only a suitable solution in attics and crawlspaces. In any other part of the building envelope, a thermal barrier is still required.

Installing a prescriptive thermal barrier over foam is often not a problem because the walls are already going to be covered with gypsum as an interior finish. The main issue tends to be in attics or crawlspaces where covering the foam with gypsum wallboard will be time consuming as well as costly. Also, the thickness of the foam is limited to the size of the rafters which can result in less insulation than what the customer would like to be installed. Because of these concerns and issues, many spray foam manufacturers have sought out alternatives to the prescriptive code. By going through thorough third-party testing, some companies have found performance based solutions that allow the foam to be installed without the prescriptive code requirements for thermal and ignition barriers. By far, the most popular of these alternatives is the intumescent coating.

Intumescent Coatings

An intumescent coating is basically a tested substitute that omits the prescriptive requirement for a thermal or ignition barrier.  The coatings are similar to latex paint. They are generally sprayed with an airless paint sprayer directly over the spray foam, after the foam has had time to fully cure. These coatings contain ground up solids that can help make the foam more resistant to heat and flame spread. The coatings are not included in the prescriptive code requirements; rather they are given specific approvals, generally through large scale testing which is documented in ICC-ES reports. These third-party reports are used by the ICC-ES to allow specific products to be used with specific thermal and/or ignition barrier substitute coatings based on various test results. Installing an intumescent coating in place of a prescriptive thermal or ignition barrier can be beneficial in that they are often a less expensive and less labor intensive alternative to the code requirements. It is important to remember that not every intumescent coating is tested or approved with every type or brand of spray foam insulation. The only way to know for sure if the product will be code compliant is to contact your spray foam manufacturer or to read your spray foam product’s associated ICC-ES report.

Although installing a prescriptive thermal or ignition barrier, or even an intumescent coating substitute, is labor intensive and adds additional cost to the job, the alternative of being non-code compliant is far worse. Also, these regulations and requirements are put into place by the ICC for safety purposes, and the safety of your customers should always be a top priority. In the future, there may be a less costly alternative or the AC-377 may change to reflect new research or testing in the spray foam insulation world. However, at least for now, we must all work together to ensure that all spray foam meets the standards set by the code counsel and industry itself.



Brandon O’Brien can be reached at brandon.obrien@demilecusa.com.

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