R-value, the performance marker for how a building envelope material will resist heat flow, plays a critical role in prioritizing a building’s energy efficiency and comfort. To help reduce building energy costs and maintain a comfortable indoor environment, many building designers specify polyisocyanurate (polyiso) insulation in the roof and wall systems. Polyiso has one of the highest R-values per inch compared to other insulation products, including mineral wool insulation. 

But here’s a question that we hear in the field: How much insulating power is really needed to meet building code requirements and improve a structure’s thermal performance? Here’s what you need to know.    

What you need to know about meeting insulation requirements  

First things first. Minimum insulation requirements are based on the climate zone your project is located in. For context, the eight different climate zones that you see depicted on the U.S. map below were determined by the International Energy Conservation Code (IECC). Essentially, these climate zones dictate many of the energy efficiency measures that a building must incorporate. They are especially relevant to building envelope design (like when it comes to determining how much R-value is needed).  

Keep in mind that a single state more than likely encompasses multiple climate zones. This makes sense when you consider how geographically diverse many U.S. states are. That’s why it’s critical to be familiar with the IECC climate zone map. A region’s distinct climate characteristics will require different building envelope design considerations to meet minimum insulation requirements.  

For accurate insulation requirements by region, refer to the latest information from the U.S. Department of Energy’s (DOE’s) Building Energy Codes Program.  

Go one step further and future-proof your project  

Still, it’s important to consider that we’re only talking about ‘minimum’ insulation requirements here. Should a building be designed to only deliver the minimum required R-value, it is possible that the building envelope will be under-insulated in a few years. After all, the minimum insulation requirements have, on average, increased 66–100 percent over the last nine years.  

So, when designing a building envelope, project teams should consider future energy requirements and associated energy costs over the entire lifespan of the installed roof or wall system. To do this correctly, experts recommend exceeding your climate zone’s present-day code by at least an additional R-10 to make sure the building continues to meet ever-evolving energy code standards.  

Next steps  

Given polyiso’s high R-values per inch, this insulating option is a top choice for project teams looking to deliver superior thermal performance in new construction and retrofits. A versatile insulation material, polyiso also resists air and moisture intrusion, further supporting building performance.  

Those ready to tap into the benefits of polyiso can turn to the Defend-R series from Drexel Metals. An all-in-one building solution, Defend-R is a complete line of roof and wall insulation panels that feature a closed-cell polyiso foam core manufactured to various facer types. The range of products makes it easier for project teams to achieve desired thermal performance in different applications.