Recommended Insulation Practices
The recommendations found in the following paragraphs will contain references to U-values and R-values. As was already stated in this chapter, the U-value is the overall coefficient of heat transfer and is expressed in Btu per hour per square foot of surface per degree Fahrenheit difference between air on the inside and air on the outside of a structural section. The R-value is the term used to express thermal resistance of the insulation. The U-value is the reciprocal of the sum of the thermal resistance values (R-values) of each element of the structural section. Table 3-5 lists the insulation recommendations for structures both in terms of R-values and overall coefficients of heat transfer in terms of U-values.
Table 3-5 Insulation Recommendations (R-Values) and Overall Coefficients of Heat Transfer (U-Values) for Major Areas of Heat Loss and Heat Gain in Residential Structures
NOTE: Insulation R-values refer to the resistance of the insulation only.
Courtesy Electric Energy Association.
ASince the thermal resistance of sandwich construction depends upon its composition and thickness, the amount of additional insulation required to obtain the maximum U-factor must be calculated in each case.