The formula for SLA in the November 2011 version of the RESNET Standard is 4 orders of magnitude too large. The multiplier is a unit conversion that is supposed to convert the denominator’s units of square feet to square inches, so as to cancel out the units of square inches in the numerator. Since there are 144 square inches per square foot, multiplying the denominator by 144 would convert the overall formula to a unit less parameter. Since 1/144≈0.00694, the formula’s multiplier should be 0.00694. After a public review and comment process the RESNET Board of Directors adopted the proposed amendment. The amendment can be reviewed at https://www.resnet.us/uploads/documents/standards/Proposed_chapter8_corrective_amendment_5_24_12.pdf The amendment will go into effect on July 18, 2012.
