Polyiso and R-value requirements

By Marcin Pazera, PIMA. 

Learn how to meet performance, code and standard requirements on your polyiso roof replacement projects. 

Commercial roof replacement projects come with a variety of unique challenges for contractors to overcome. One of the main ones is making sure the roof they are installing complies with local energy codes’ R-value requirements. An R-value is a measurement of an assembly’s resistance to heat flow. Many codes require a higher R-value, which indicates that a roof has more thermal insulation, resulting in lower heating and cooling costs due to increased energy efficiency. In this article, we take the expert knowledge from Polyisocyanurate Insulation Manufacturers Association (PIMA) to dive into how contractors can use polyiso to meet these performance standards and requirements.  

Polyiso continues to be the leading solution due to its high R-value per inch compared to other insulation options. Available in multiple forms, including flat stock boards, tapered insulation and high-density (HD) cover boards, polyiso rigid roof insulation offers flexibility in design and installation. When installed in accordance with manufacturers’ installation instructions, polyiso roof insulation products can enhance energy efficiency, durability and code compliance across reroofing projects. 

Install multi-layered systems with staggered joints in rigid roof insulation 

To maximize energy efficiency in reroofing projects, roofing contractors should install polyiso rigid roof insulation in a multi-layered system with staggered joints. This best practice minimizes thermal bridging between board joints and reduces the opportunity for air and moisture movement through the roof system. When adhered over a mechanically attached base layer, the top layer in a multi-layered system can also be used to bury fasteners to further reduce thermal bridges. All of these practices are key factors in improving building envelope performance and long-term durability.  

Staggered joints in a commercial roof insulation system also help reduce the possibility of membrane buckling. These performance enhancements support a more resilient and energy-efficient building envelope. 

Utilize polyiso tapered insulation to enhance thermal performance and drainage 

Certain conditions can complicate insulation upgrades in reroofing projects. This includes low curb or flashing heights, existing roof drainage configurations or door thresholds and window sill heights that sit too close to the finished roof surface. In many of these situations, a combination of flat stock polyiso board and polyiso tapered insulation can be used for targeted increases in R-value while accommodating limiting site conditions. 

The flexibility in polyiso tapered insulation system designs is beneficial for retrofit projects where roofs lack proper drainage slopes, but structural modifications are impractical or cost-prohibitive. In such projects, integrating tapered polyiso insulation can contribute to enhanced thermal performance as well as help mitigate ponding water to improve overall roof system durability. 

Improve commercial roof durability with high-density (HD) polyiso cover boards 

“Incredibly versatile, polyiso can function as a dual role product — it can be insulation and also a cover board,” Natalie Tobey, product marketing manager at Carlisle Construction Materials, highlighted.  

HD polyiso roof cover boards are an advanced building technology that protects the roof system from consistent service traffic, extreme weather events (such as hail or high winds) and even the added loads of installed rooftop solar systems. “HD polyiso cover boards can provide the compressive strength needed for most roof systems to meet extreme weather criteria, including the Severe Hail classification requirements,” Natalie explained. 

“But unlike traditional gypsum boards, HD polyiso cover boards also contribute to the roof assembly’s total R-value with their polyiso core,” she noted. This added insulation can reduce the overall amount of insulation needed to meet energy codes when compared to designs that utilize traditional gypsum cover boards. The multifunctional quality of polyiso HD cover board helps contractors simplify roof system design and reduce labor and material costs. 

Staying ahead 

Contractors looking to stay competitive in the reroofing market must ensure every project aligns with local codes and national standards. To help industry professionals determine the energy performance requirements for the states they work in, PIMA has created State Energy Code Fact Sheets, which provide a state-by-state detail of the minimum insulation requirements for low-slope commercial roofs in both new and existing buildings.  

Learn more about the energy code requirements applicable to your next roofing project. 

Original article source: Polyisocyanurate Insulation Manufacturers Association (PIMA).