Insulation Requirements for wall assemblies — Did You Know?
Did you know that Fire Rated Wall Assemblies built with Fire Retardant Treated Wood (FRTW) have precise insulation requirements that spell out the exact material, thickness and density you’re required to use? If you’re a builder, architect, engineer, you more than likely know that your local energy code requires specific minimum insulation requirements for your everyday wall assemblies. Did you know that these two insulation requirements are independent of one another?
Let’s say your local code requires minimum R-21 insulation in the walls. The R-21 materials meet the code for your common insulation applications EXCEPT for your Rated Wall Assemblies, or to be more precise for the sake of our conversation, Fire Rated Wall Assemblies.
What does the common Fire Rated Wall Assemblies consist of (from the inside of the wall)?
- Interior Drywall or Gypsum Wall Board of some specific thickness & type
- Fire Retardant Treated studs with specified o/c spacing
- Insulation with a specific material, thickness, and density requirements
- Fire Retardant Treated wood sheathing
- Exterior façade (or facing) allowed for use with the rated assembly (for exterior walls)
So why is insulation such an important component of a Fire Rated Wall Assembly?
Insulation reduces the exchange of energy (heat) through a surface such as a wall, attic, duct or roof. So with an assembly that is supposed to withstand HEAT, utilizing the right kind of insulation becomes quite important. Without the right kind of insulation, and in the best-case scenario, the wall assembly will fail the testing regimen, but in the worst-case scenario, the wrong insulation installed in a Fire Rated Wall Assembly could potentially lead to the loss of life and/or structural failure of epic magnitude. In short, insulation “insulates” the combustible wood-frame from heat and provides added resistance to fire, among other more commonly known insulation tasks such as “keeping my building cool during the summer months.”
As a firefighter, specifically when working as an aircraft firefighter, we were exposed to extreme heat when fighting fuel and/or aircraft fires. To prevent this ridiculous heat from deterring us from doing our jobs (putting the wet stuff on the red stuff, or rolling on the foam) we wore special firefighting gear that provided multiple forms of insulation from the effects of fire ~ heat. Additionally, and due to the radiant heat generated by these large fires, the exterior of our bunker gear was made of a shiny material that helped reflect that radiant heat which often melted face shields, truck lights & beacons, and signed any exposed body hair. So, if the insulation of a firefighter when doing their job is MISSION CRITICAL, then the same can be said of Fire Rated Wall Assemblies; they too require precise insulation, in varying forms, to do their jobs, otherwise, these assemblies would not last when subjected to fire. They would fail!
Insulation materials in wall assemblies run the gamut of bulky fiber materials such as fiberglass, rock and slag wool, cellulose, and natural fibers to rigid foam boards to sleek foils that reflect energy; there’s all kinds of stuff available on the market. The difference amongst these materials is (a) they’re different, but (b) they all have varying densities, thicknesses, R-Values, end-uses, exposures, etc., and of course, with all the different options, cost becomes a major factor to consider.
FlameTech Fire Rated Wall Assemblies allow for the use of 3-1/2” (2×4 framing) 5-1/2” (2×6 framing) thick R-13 fiberglass batt insulation, the general everyday stuff you see on jobs. Our competition’s Fire Rated Wall Assemblies, for the most part, were tested and certified with costlier R-15 high-density fiberglass insulation and/or mineral wool insulation. By the way, if a Fire Rated Wall Assembly is not built as tested & certified, and in accordance with the Rated Wall Design, meaning that the correct components were utilized in the construction of the wall assembly, it’s a Building Code Violation. In other words, to remain within the design criteria, the assembly must be constructed as specified in the published design.
So how is one FRTW assembly allowed to use one kind of insulation, and another assembly must use another type of insulation?
Simply put, and without getting all technical, some Fire Rated Wall Assemblies are much higher performing than others because of the base FRTW lumber & plywood products being used (there are different brands), and can therefore obtain hourly Fire Resistance Ratings using cheaper assembly materials, while other assemblies and their base FRTW products may have been developed eons ago and therefore require more robust insulation requirements so they can obtain a specific Hourly Fire Resistance Rating.
Selecting your Fire Retardant Treated Wood.
The next time you select a brand of FRTW lumber & plywood, you must consider the overall cost of the Fire Rated Wall Assembly and this has everything to do with what the assembly is composed of. Are you simply selling cheap lumber, cheap drywall, cheap insulation and framing to get the job, and are you selling the correct materials to support the Fire Rated Wall Assemblies? Your customer depends on you for this knowledge and value.
How do you know if you’re using the correct insulation on your job?
Always refer to the Fire Rated Wall Assembly Design (example: FlameTech 2-Hr Fire Rated Wall Assembly) and associated Design Number to review the required/specified materials, and read ALL the details, including the fine print. There are often many references to the code that are hard to find, asterisks annotating special requirements for use with “this and that”, etc. Some manufacturers have made some clever propaganda/marketing materials with colored insulation allowing you to make an assumption about what kind of insulation is allowed for use. You remember what folks say about assuming, right?
So why the big fuss? This insulation requirement in Fire Rated Wall Assemblies is a major issue, that in our opinion, has been totally missed and long overlooked. Most want cheap solutions and some are willing to cut corners just to put money back in their pocket. Our focus is on preserving life and property in concert with building code requirements through the manufacturing, specification, and sale of high-performance treated wood products, and we’re good at what we do!