EPS thermal insulation meeting American Society for Testing and Materials (ASTM) C578 type I (0.9 lb/ft3 minimum density) has a typical R-value of 3.8 per inch, whereas the higher-density type IX (1.80 lb/ft3) boards are approximately 4.35 per inch. Board thickness ranges from V2 to 36", and lengths up to 24 ft are available depending on the supplier and end use (Fig. 11.4).
Stable or stabilized R-value refers to the quantitative ability of a foam insulation material to retain its as-manufactured R-value. Over time, some foam insulations lose their blowing agent and with it up to 25 percent of their R-value. This process is called thermal drift As long as the EPS foam is kept dry, the R-value is permanent because its cellular structure contains only stabilized air.5 Even if allowed to absorb some moisture, it appears that EPS retains its R-value.
R-Value* at 40° and 75* F
”AFM Type I EPS AFM Type VIII EPS AFM Type II EPS AFM Type IX EPS Standard (Nom. 1.00 pcf) (Nom. 1.25 pcf) (Nom. 1.50 pcf) (Nom, 2.00 pcf)
Design Consideration: System R-Values can be increased approximately 2.5 with the use of a bright foil laminate. A minimum 1 /2" air space on the reflective foil surface of the sheathing is required to achieve this additional R-Value. (Reference: ASHRAE Handbook Fundamentals)
R-Value means resistance to heat flow. The higher the R-Value, the greater the insulating power.
** Types designated by ASTM C 578 Specifcation Standard.
AFM EPS size and number of pieces per package vary. Check label on package. Manufacturer has fact data sheet on file and is available on request.
Board sizes supplied normally range from 4‘ x 8′ to 4′ x 9′, up to 4" thick. Other sizes can be provided for special conditions as required.
ю Figure 11.4 EPS R-values. (R-Control Building Systems)
Published data on EPS indicate that even at 7.0 percent moisture by volume, EPS retained 90 percent of its R-value. (Most listings for absorption by volume list about 3 percent as the normal limit.6)