# R-value

Although the typical R-value is 3.2 per inch, R-values can range from 3.04 to 4.3 for fiberglass blanket insulation. In addition to bag labeling, R-values are also printed on the facings of batts and rolls. Unfaced insulation is coded with stripes or ink-jet-printed to iden­tify the R-value. The most common R-values in standard sizes for fiberglass insulation are R-ll, R-13, and R-15 for 3V2M-thick prod­ucts; R-19, R-21, and R-22 for 572M-thick products; and R-25, R-30, and R-38. One manufacturer’s table of standard sizes and R-values for batt insulation is shown in Fig. 8.6.

If greater R-values are desired, it is possible to install multiple layers of blanket insulation where there is adequate space. Since R-values can be added, thermal calculations are simple. For exam­ple, if a ceiling requires R-38 insulation, then two layers of R-19 batts or rolls can be used. Only one layer should have a vapor retarder, facing the correct side of the wall depending on the cli­mate, while additional layers normally should be unfaced. It is

 R-Value Thickness Width R RSI in. (mm) in. (mm) UNFACED 8 1.4 21/2 (64) 16 & 24 (406 & 610) 11 1.9 3V2 (89) 111/4, 15, 151/4, 19, 23, 231/4, (286,381,387, 483,584, 591, 44, 48 & 84 1118, 1219 & 2134) 13 2.3 3V2 (89) 151/4, 16, 231/4 & 24 (387, 406, 591 & 610) 15 2.6 31/2 (89) 151/4 & 23’A (387 & 591) 19 3.3 6V4 (159) 11, 111/4, 15, 151/4, 16, 19, (279, 286,381,387, 406, 483, 23, 231/4, 24 & 48 584, 591,610 & 1219) 21 3.7 5V2 (140) 15, 151/4 & 231/4 (381, 387 & 591) 25 4.4 8 (203) 15, 16, 19, 23, 24, 32 & 46V2 (381,406, 483, 584, 610, 813 & 1181) 30 5.3 10 (254) 16, 19 & 24 (406, 483 & 610) 30C* 5.3 8V4 (210) 151/4 & 231/4 (387 & 591} 38 6.7 12 (305) 16 & 24 (406 & 610) 38C* 6.7 10 (254) 151/4 & 231/4 (387 & 591) KRAFT-FACED n 1.9 31/2 (89) 11, 15, 16, 23 & 24 (279, 381,406, 584 & 610) 13 2.3 31/2 (89) 11, 15, 16, 19, 23 &24 (279, 381,406, 483, 584 & 610) 15 2.6 31/2 (89) 15 & 23 (381 & 584) 19 3.3 61/4 (159) 11, 15, 16, 19, 23 & 24 (279, 381,406, 483, 584 & 610) 21 3.7 51/2 (140) 15 & 23 (381 & 584) 22 3.9 8 (203) 15, 19 & 23 (381,483 & 584} 25 4.4 8 (203) 15 &23 (381 & 584) 26 4.6 8 (203) 16 & 24 (406 & 610) 30 5.3 10 (254) 11, 15, 16, 19, 19V4, & 24 (279, 381,406, 483, 489 & 610) 30C* 5.3 8V4 (210) 15 & 23 (381 & 584) 38 6.7 12 (305) 16 & 24 (406 & 610) 38C* 6.7 10 (254) 15 & 23 (381 & 584)
 *Cathedral Ceiling Batts

Figure 8.6 Batt insulation specifications. (CertainTeed) important not to compress the blankets to a less than normal thick­ness during installation because the rated R-value will be reduced.

The popularity of cathedral ceilings over the last 10 years has cre­ated the demand for a modified type of blanket insulation. R-30 and R-38 fiberglass insulation batts are 10 and 12", respectively. These sizes are too thick when placed between nominal 2 X 10 or 2 X 12 framing members, and still maintain the 1" continuous airspace required by most building codes for roof-ceiling ventilation require­ments. Known as high-performance or high-density batts, the mod­ified R-30 and R-38 insulations typically are designated with a “C” suffix. The R-30 superbatts are 8V4 to 8V2" thick, as opposed to stan­dard R-30 fiberglass batts of 972 to 10". (Thickness may vary by manufacturer.) R-38 superbatts are 10 to 10V4" thick, as opposed to standard. Since these batts achieve the same R-value as the thick­er types, they do not need to be compressed to fit the angles and spaces typically found in cathedral ceilings. Because they contain more fiberglass, these higher-density batts are more expensive than low-density batts. Similarly, medium-density batt insulation is also becoming increasingly popular. Measuring the same thickness as R – 11, a 372"-thick batt can now achieve R-values of 13 or 15.