Fiberglass blanket insulation products are manufactured to fit in both 2X4 and 2X6 wood frame construction. Standard sidewall widths of both 15 and 23 in are available. If steel stud framing is used, 16- and 24" widths are available for steel stud construction. R-ll, R-13, and R-15 are used in nominal 4" walls, whereas R-19 and R-21 are used for nominal 6" walls (Fig. 8.7).

It is important to note that proper installation is necessary in order to guarantee that the actual R-value achieved is the R-value intend­ed. For example, homes built with 2X6 construction typically use a standard R-19 batt that measures 6 to 63/4" thick to fill a 572" wall cav­ity. Compressing the insulation causes it to lose some of its thermal effectiveness, reducing its R-value to approximately R-18. Using an R-21 high-density batt that measures 572" thick guarantees that there is no compromise to the R-value during installation.