There is a lot of confusion when it comes to thermal barriers regarding what they are and when they are needed with spray foam application. Luckily, we understand this subject and will explain the thermal barrier and the International Residential Code (IRC) in a way that you can understand.
What is a thermal barrier?
A thermal barrier is a material that is applied between spray foam insulation and the interior living space. Moreover, the IRC says that all foam plastic insulations have to be separated from the interior of the building by a 15-minute thermal barrier. One such barrier is half-inch gypsum board (drywall). Because any type of spray foam is combustible, along with most other building materials, we need to protect the wall from the foam. By installing gypsum board over the foam, we have protection on the inside of the building for a life-saving purpose.
The IRC is trying to provide enough time for occupants to get out of the house in case of fire. A thermal barrier will give an occupant about 15 minutes to escape.
Not every area of your home has to have a thermal barrier. So, what needs to be covered and what can be exposed?
Can spray foam be left exposed?
The quick answer is yes and no, because spray foam can be left exposed in some areas of the home with other areas requiring a thermal barrier, according to the code.
If the area of the home that has been sprayed with foam is directly connected to the living space or used for storage, then it has to be separated by a thermal barrier. This would be your exterior walls and ceilings.
There are exceptions to the rule, which are the crawl space, attic, and basement rim joists. Rim joists never require thermal barriers, and attics and crawl spaces that are not used for storage or living space do not need a thermal barrier. They’re already treated with an ignition barrier. The only time a crawl space or attic needs a thermal barrier is when the space is used as an auxiliary living space or storage.
There are a couple of ways to omit or provide an alternate to the thermal barrier. One of those is large scale test using something like a cementitious-based product. If it passes the test, it can be used as a stand-alone thermal barrier.
You could also use an intumescent coating (swells up when heated). It has been tested over a specific spray foam to provide an interior finish system that acts like a thermal barrier. For example, if you’re going to install spray foam on the underside of a roof deck in an open roof assembly like in a restaurant, you would put the spray foam on the underside. You can’t leave it exposed to the inside of the building, so you’ll need to use a thermal barrier to go over it, such as drywall or thermal barrier paint. What do we do?
If you have an intumescent coating that has been approved, then you apply that over the spray foam. The coating is now an interior finish that we can leave exposed inside the restaurant, which meets interior standards.
Learn more about insulation code
In conclusion, you now have a grasp of thermal barriers, but you might have more questions about meeting insulation code in your area.
If you want to make sure your new home or remodeling project meets code, please contact us.
- Spray Foam Advisor, Thermal Barriers, Sep 29, 2017, sprayfoamadvisor.com
- Retrofoam of Michigan, What is a Thermal Barrier and When is it Needed with Spray Foam? December 26, 2018, retrofoamofmichigan.com