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Increasing the thickness of polyiso roof insulation above code requirements saves money and energy.

A recent study released by the Polyisocyanurate Insulation Manufacturers Association (PIMA) demonstrated that increasing the thickness of polyiso roof insulation not only provides a positive rate of return on the cost of installation but also reduces energy costs and harm to the environment. The purpose of the case study, conducted by Energy Services Provider Group (ESPG), an independent energy analyst in Maryland, was to measure the economic and environmental effects of additional thickness of polyiso roof insulation, over the minimum code requirement. Building energy costs were calculated for buildings in seven US cities: Boston, Chicago, Los Angeles, Dallas, Seattle, Denver and Atlanta. The study examined two types of facilities: a retail building and an elementary school. A “model” of each facility, based on a statistical database of 25 years of energy simulations, was referenced. The current ASHRAE 90.1-1999 standards for roof insulation were used as the baseline for the minimum roof insulation requirements.

This database defined the typical retail building as a single-story, 100,000 square-foot structure (two-to-five length/width ratio) with 30% glazing. The structure was cooled to 78ºF in the summer and heated to 72ºF in the winter. Unoccupied temperatures were maintained at 90ºF in summer and 55ºF in winter. This database also defined the typical elementary school as a single-story, 65,000 square-foot structure (two-to-five length/width ratio) with 30% glazing. The structure was cooled to 75ºF in the summer and heated to 72ºF in the winter. Unoccupied temperatures were maintained at 90ºF in summer and 60ºF in winter. Using the “models,” energy simulations were run for the different locations with their corresponding utility rates to establish the comparisons. In addition, the impact of these savings on the environment was assessed.

Results: Retail buildings In each city, except for Los Angeles, the ASHRAE specified minimum insulation value equates to two inches of polyiso roof insulation. In Los Angeles, the ASHRAE specified minimum insulation value equates to one inch of polyiso roof insulation. Using this as the baseline case, the study found that increasing the insulation thickness by one inch or more in retail buildings:

  • Provides a significant rate of return to users for the
    financial investment of installing additional polyiso insulation.
  • reduces the costs to facilities on the average of
    $2,500 per year.
  • reduces CO2 emissions by thousands of pounds.
  • SO2 emissions by thousands of grams.
  • NOX emissions by thousands of grams per year.

Results: Elementary schools in each city, except for Los Angeles, the ASHRAE specified minimum insulation value equates to two inches of polyiso roof insulation. In Los Angeles, the ASHRAE specified minimum insulation value equates to one inch of polyiso roof insulation. The study concluded that the environmental impact of these energy savings in elementary schools equates to significant reductions in CO2 emissions, SO2 emissions and NOX emissions.

Due to the unoccupied summer months, the overall energy savings for elementary schools is low. However, the savings in operating costs and energy use are still significant. In addition, users receive a positive rate of return on their investment.

“Polyiso roof insulation continues to perform exceedingly well in study after study,” said Jared O. Blum, president of PIMA. “This study simply reflects the quality product that our manufacturers have been providing for years and emphasizes the significant positive rate of return that users receive for
investing in our product.”


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