Boosting roof efficiency with HD polysio cover boards

By Polyisocyanurate Insulation Manufacturers Association (PIMA). 

Using HD polyiso cover boards can reduce installation time, improve energy performance and strengthen the long-term reliability of roof systems. 

High-density polyiso cover boards are becoming a preferred choice for modern roof assemblies, offering durability and thermal performance in a single solution. The Polyisocyanurate Insulation Manufacturers Association (PIMA) highlights that these boards provide meaningful insulating value, delivering approximately R-2.5 at a standard 0.5-inch thickness, which can help roof systems meet or exceed prescriptive energy code requirements for insulation installed entirely above the deck. When paired with polyiso insulation, these cover boards strengthen the thermal layer of the assembly and support compliance with the International Energy Conservation Code and ASHRAE Standard 90.1. 

For reroofing projects where deck height limitations restrict how much insulation can be added, maximizing R-value per inch becomes essential. Using high-density polyiso cover boards allows project teams to increase total thermal resistance without significantly increasing roof thickness. PIMA notes that some manufacturers also offer composite boards that combine a high-density cover board with polyiso insulation in one product, streamlining installation and reducing labor time while maintaining the performance needed for energy-efficient roof systems. 

Energy code compliance with HD polyiso cover boards 

Under current versions of the International Energy Conservation Code and ASHRAE Standard 90.1, roof assemblies with insulation installed entirely above deck (IEAD) are required to meet minimum continuous insulation requirements. The minimum insulation requirements apply to both new construction and roof replacement projects on existing buildings. For roof replacement projects, maximizing the R-value per inch can be critical when existing rooftop conditions present thickness limitations. 

Minimum R-value requirements for roof assemblies typically range from R-25 to R-35 depending on the climate zone. The assembly configurations below demonstrate how HD polyiso cover boards can be combined with polyiso roof insulation to meet these minimum energy code requirements. Figures 2a-2c also include the thickness savings when HD polyiso cover boards are installed compared to assemblies that use insulation with a traditional gypsum cover board to meet the applicable energy code requirements. 

Why R-value matters in cover boards 

• Optimized design: Cover boards that are rated as an insulating material can reduce the thickness of insulation required to meet minimum energy code requirements. 
• Thickness limitation: Roof replacement projects can present unique challenges when energy codes require the installation of increased insulation levels on existing buildings. Installing HD polyiso cover boards with an R-value of 2.5 maximizes energy efficiency on a per inch basis when compared to traditional cover board products. 
• Energy loss: Mechanically attached roof systems installed with conductive fasteners create thermal bridges and reduce the overall energy efficiency performance of the roof system. HD polyiso cover boards can be installed with adhesives on top of mechanically attached polyiso insulation base layers effectively burying the fasteners below a thermal layer. This can reduce the impact of thermal bridges and increase the performance of the roof system. 

Additional benefits 

HD polyiso cover boards deliver enhanced roof protection and energy savings all in one product, but the advantages go beyond energy efficiency: 

• Widely available from more than 40 manufacturing sites in the U.S. and Canada. 
• Reduced freight with single source shipping of both insulation and cover board products. 
• Available in various compressive strengths, facers and board sizes to meet your project specific needs. 
• Lightweight boards for ease of installation. 
• Easy to cut without the need for special tools and virtually dust free. 

Before installing HD polyiso cover boards, project teams should always consult manufacturer data sheets for information on product performance and installation instructions. 

Original article and photos source: PIMA