When it comes to insulating your home or commercial building, one number matters more than any other — the R-value. But with so many insulation products on the market, each claiming superior performance, how do you know which R-value is right for your specific project and climate zone?
This guide breaks down everything you need to know about R-values — what they mean, how they are measured, and how to choose the right ThermBoard® panel for your project.
What Is R-Value?
R-value is a measure of thermal resistance — how well a material resists the flow of heat. The higher the R-value, the better the insulation performs. A wall with a higher R-value will lose less heat in winter and gain less heat in summer — resulting in lower energy bills and more consistent indoor temperatures year-round.
R-value is measured per inch of material thickness. This means that thicker insulation panels deliver higher R-values — but the density and material type also play a critical role. ThermBoard® rigid insulation boards deliver significantly higher R-values per inch than conventional fiberglass batt insulation — making them the more efficient choice for any application.
Why Climate Zone Matters
The United States is divided into eight climate zones — from the hot humid south to the cold subarctic north. Each zone has different minimum R-value requirements for walls, roofs, and floors — set by the International Energy Conservation Code (IECC).
Building in a colder climate zone requires higher R-values to prevent heat loss in winter. Building in a hotter climate zone requires sufficient R-value to prevent heat gain in summer. ThermBoard® is available in multiple thicknesses to meet the requirements of any climate zone — from R-13.3 for mild climates to R-28.5 for the most demanding cold climate applications.
ThermBoard® R-Value Options
ThermBoard® rigid insulation boards are available in three standard thicknesses:
3.5 inch panel — R-13.3
Ideal for interior walls, mild climate zones, and light retrofit applications. Meets minimum code requirements for walls in Climate Zones 1-3.
5.5 inch panel — R-21
The most popular choice for exterior walls and standard new construction. Meets or exceeds code requirements for walls in Climate Zones 4-6 and provides excellent performance in roofs and floors.
7.5 inch panel — R-28.5
Maximum performance for roofs, cold climate walls, and high-performance building applications. Exceeds code requirements in all climate zones and is the preferred choice for net-zero and energy-efficient building projects.
The Real-World Difference
Laboratory R-values and real-world R-values are not always the same. Conventional fiberglass batt insulation is rated at the center of the insulation cavity — but wooden studs create thermal bridges that reduce whole-wall R-value by up to 30%.
ThermBoard® continuous rigid insulation eliminates thermal bridges entirely — delivering its full rated R-value across the entire wall surface, not just at the center of the cavity. This means that a ThermBoard® wall with a rated R-value of R-21 actually performs at R-21 in the real world — not R-14 or R-15 after accounting for thermal bridging.
How to Choose the Right ThermBoard® Panel
Choosing the right ThermBoard® panel for your project is straightforward:
- Identify your climate zone using the IECC climate zone map
- Check the minimum R-value requirements for your application (wall, roof, or floor)
- Select the ThermBoard® panel thickness that meets or exceeds your requirement
- Contact our team if you need help specifying the right panel for your project
Our team is available to provide free specification support for any residential or commercial project — helping you select the right panel thickness, R-value, and facing for every application in your building envelope.
Get Started
Ready to spec ThermBoard® for your next project? Browse our full range of rigid insulation panels or contact our team for a free specification consultation.