Atlas Molded Products provides truth and insight on ASTM D578 and D6817

ATLANTA, Ga. (GLOBE NEWSWIRE) —  Lightweight and versatile, molded polystyrene foam is a commercial building material that though common remains misunderstood.

“Molded polystyrene is versatile, efficient, and solves a lot of common challenges,” says Dale Mullikin, a National Account Director for Atlas Molded Products. The molded polystyrene products available from Atlas include structural materials and insulations for commercial construction with compressive strengths ranging from 15 psi up to 60 psi. Molded polystyrene’s thermal insulation capacities are also exceptional making it ideal for high-performance building envelopes.

Some of the confusion surrounding rigid cellular polystyrene materials is that molded polystyrene can be used as both an insulation and a structural fill, known as geofoam. Though the materials are identical, within ASTM International standards there are two separate designations, ASTM C578 for insulation and ASTM D6817 for geofoam.

Rigid cellular polystyrene was first tested and published in ASTM standards under ASTM C578 “Standard Specification for Rigid, Cellular Polystyrene Thermal Insulation”. All rigid cellular polystyrene fell under C578 until 2002 when ASTM D6817 was introduced specifically to account for structural applications using geofoam. Many architects still think of these products exclusively as insulations and problematically, the original structural capacities listed in the insulation standard for XPS materials are inadequate without adjustment factors. Structural loading should always be specified using the structural capacities in ASTM D6817.

ASTM D6817 “Standard Specification for Rigid Cellular Polystyrene Geofoam” determines the structural capacity of rigid cellular polystyrene by compressing the material until it is deformed by only one percent. Conversely, the insulation specification, ASTM C578, compresses the same material until it is deformed by ten percent. C578 is meant to compare two types of materials against one another. D6817, however, defines the loading capacity the material can support indefinitely when used structurally.

While both molded polystyrene and XPS materials are capable of supporting structural loads, molded polystyrene is much more efficient to build with. XPS insulation is manufactured in flat, rigid sheets a few inches thick and must be stacked. Atlas molds polystyrene blocks as large as 8’ x 4’ x 36”-thick. Despite their size, blocks this large can easily be moved by hand, allowing builders to easily install large structural fill using manual labor. Using hot wire cutters, the blocks are easy to customize to fit around obstacles like pipes or columns.

“Atlas Molded Products wants to ensure the incredible capacity and versatility of molded polystyrene is understood,” says Mullikin.