Roofing Insulation Overview

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Roofing Insulation Overview

If you want an energy-efficient roof, the first place to start is insulation. Proper insulation is one of the most important contributors to a building’s energy efficiency. Having a high R-value for your roof, the common measurement of thermal resistance, can also aid in achieving LEED® v4 and RoofPoint(TM) certifications.

 

What’s Recommended

The National Roofing Contractors Association (NRCA) recommends using two layers of insulation. This can be comprised of two layers of insulation boards or a single layer of insulation and a cover board.  Always follow your local building codes when choosing the materials for a roof.

 

Comparison of Three Types of Foam Insulation

 

Type Advantages Caveats
Polyisocyanurate (Polyiso)
  • Popular, used in >70% of new and reroofing projects
  • High R-value, 5.7 per inch
  • Doesn’t soften or melt at 250° F, meets fire code for direct to steel decks installations without a thermal barrier
  • Lightweight
  • Moisture resistant
  • Easy to cut and install
  • Environmental-friendly choice since it is made of recycled material, zero-ozone depletion potential
  • Available in flat or tapered cuts
  • Compatible with adhesive attachment
Must be used with a cover board if using asphalt
Extruded Polystyrene (XPS)
  • R-value of 5 per inch
  • Lightweight
  • High-compressive strength
  • Moisture resistant
  • Available in flat or tapered cuts
  • Softens at 165° F and melts at 200° F, not fire rated so requires a thermal barrier such as glass mat gypsum board when used on metal/steel decks
  • Not compatible with asphalt and adhesive attachment
Expanded Polystyrene (EPS or Bead Board)
  • Relatively inexpensive
  • Lightweight
  • Widely used in tapered systems
  • Available in flat or tapered cuts
  • Lower R-value (4 per inch but might vary with density)
  • Softens at 165° F and melts at 200° F, not fire rated so requires a thermal barrier such as glass mat gypsum board when used on metal/steel decks
  • Low durability
  • Absorbs water
  • Not compatible with asphalt and adhesive attachment

Cover Boards

Cover boards go on top of the insulation layer, protecting it from hot asphalt and adhesives. Depending on the cover board type, they can also protect the roof from fire, moisture, foot traffic, loads and provide thermal resistance. In fact, the NRCA recommends cover boards for all roofing systems. GenFlex has a wide selection of different types of cover boards to meet your needs. Here are three of them:

  • Structodek(R) is a great choice if you are looking for lightweight, high-density, wood fiber cover board.
  • HD ISO is well worth considering since it is lightweight, strong (aids in protecting against hail damage, foot traffic and other loads), energy efficient, easy to cut, moisture and mold resistant, wind resistant, fire resistant and available in either flat or tapered boards.
  • Coated Glass Facer Polyiso provides outstanding fire, wind and thermal performance for single-ply and modified bitumen commercial roofing applications.

If you are interested in learning more about insulation and cover boards, GenFlex University has a great online-education course about them. For design assistance or to request a quote, please contact estimatingservicesdept@genflex.com.