How to Compare the Energy Loss of Structural Insulated Panel and Traditional Roof Systems

Different types of roofing insulation result in varying levels of energy loss.

Structural insulated panel is one of the most effective types of insulation, allowing remarkably little heat to seep through. This results in very low degrees of energy loss through the roof, when compared to traditional roofing systems. Comparing your current roof to a hypothetical one with structural insulated paneling can help you determine whether it is more cost-effective to make the switch. You can perform this comparison with only a couple short calculations, taking into account the factors that influence the loss of heat energy.

Instructions

1. Measure the surface area of the roof you want to use in your comparison. To do this, write down the width and length of each flat surface on the roof. Multiply each pair of numbers and add the results together for the total area, or A.

   For example, given a house with a simple sloped roof, both sides of which measure 40 by 20 feet, this equation would look like (40 --- 15) + (40 --- 15) = 1,200.

2. Subtract the lowest annual exterior temperature from the interior temperature of your house, measured in degrees Fahrenheit. This is the temperature difference, also known as "T.

   For example, given an inside temperature of 60 degrees and an outside low of 16, this equation would look like 60 - 16 = 44.

3. Find the capacitance of your current roofing material or other traditional roof system, if you're working with a hypothetical situation. This is expressed as a U-value, a number less than 1 that indicates the percentage of heat the material allows to pass through it. Charts with common U-values can be found in both books on heating and on several websites.

   For example, given a house with a built-up roof, no attic and R2 ceiling insulation, this number would be 0.197.

4. Multiply the various values, with A --- U --- "T = Q, the heat energy loss in British Thermal Units, or BTUs, per hour. Most structural insulated panels have a U-value of approximately 0.17, so multiply A --- 0.17 --- "T to find the energy loss of a hypothetical roof of your dimensions with structural insulated paneling installed. Compare the two numbers.

   For example, given the data calculated in the previous steps, the equation would be 1,200 --- 0.197 --- 44 = 10,402 BTU/h. With structural insulated paneling, the equation would be 1,200 --- 0.17 --- 44 = 8,976 BTU/h, saving 1,426 BTUs hourly.

References

• Process Heating; Calculating Heat Loss; Mark Crombie
• SIP Build: Benefits of Structural Insulated Panels

Resources

• Delta-T Inc.: U-Value Charts