Engineering Tables - Max. Allowable Loading by Size/Roof Insulation Type

DECK INSULATION	STRESS	SMALL BASE	MEDIUM BASE	LARGE BASE
Expanded Poltstyrene Glass/Mineral Fiber   Polyisocyanurate Extruded Poltstyrene Fiber Board    Perlite    Cellular Glass	5 psi 5 psi 5 psi 6 psi 6 psi 17.5 psi 50 psi	770 pounds 770 pounds 770 pounds 924 pounds 924 pounds 2,695 pounds 7,700 pounds	720 pounds 720 pounds 720 pounds 864 pounds 864 pounds 2,520 pounds 7,200 pounds	1,620 pounds 1,620 pounds 1,620 pounds 1,944 pounds 1,944 pounds 5,670 pounds 16,200 pounds

Please note that the placement of individual bases must be reviewed by a Structural Engineer to ensure that the roof structure is not overloaded.

Based on a factor of safety of 2 against published minimum ultimate values of insulation compression strength
(NRCA Commercial Low-Slope Roofing Materials Guide, 1994 Edition). Designer must also ensure adequacy
against punching resistance and overall structural integrity of the roof on which the assembly is placed.
Resultant stresses from lateral loads on pipes may result in higher stresses in substrate than plain gravity loads.