EPS (Expanded Polystyrene Foam)

NOTE:See also Accepted Roof Deck Insulation products by clicking on this link.

(See also Extruded Expanded Polystyrene Foam)

Third Party Certification: RGC welcomes and accepts the industry recommendation presented by all EPS manufacturers currently active in the B.C. market to require third party certification of the EPS products meeting CAN / ULC-S701-97 / (CAN / CGSB-51.20-M87) requirements. It is understood that such a certification program requires annual inspections / recertification by an independent testing lab.

Molten polystyrene and a blowing agent are mixed and formed into uniform closed-cell structures (“beads”). These are later expanded up to 40 times by steam in a pre-expander. (The amount of expansion determines the density and, therefore, the thermal conductivity of the final product.) The expanded beads are stabilized in curing bins, fused into a billet in a block mold, and cut into the desired size, shape and thickness. This process produces rigid boards of interconnecting closed cells of densities varying from 16 to 48 kg / cu.m (1 to 3 lb / cu.ft). Expanded polystyrene insulation is commonly referred to as “beadboard” or “popcorn”.

Expanded polystyrene roof insulation is presently manufactured to the CAN / ULC-S701-97 / (CAN / CGSB-51.20-M87) standard and is available in four types, depending on the physical properties of the material. Basically, the strength (tensile, compressive, flexural, and shear) and thermal resistance properties increase, and the water vapour permeance and water absorption properties decrease from Type 1 to Type 4. (For Type 2 and Type 4 see also section 6 above, Extruded Expanded Polystyrene). Note: Type 4 is usually, if not always, extruded.

Expanded polystyrene foam roof insulation is combustible and, when used on steel decks or over a roof that is subject to fire exposure from below, a fire-rated underlayment or thermal barrier (such as gypsum board) may be required between the roof deck and the insulation (consult Building Code and insurance requirements).

Expanded polystyrene foam roof insulation provides the following properties and advantages:

• Compatible with asphalt
• Resistant to the effects of moisture
• Resistant to cell deterioration (durable)
• Resistant to impact
• Resistant to thermal conductivity
• Stable K-value (the thermal conductivity does not change with aging)

The possible disadvantages or precautions involved in the use of expanded polystyrene roof insulation include:

• Flammable (combustible)
• Affected by solvents (i.e. adhesives and cleaners used for single-ply membranes)
• Heat sensitive [requires an insulation overlay (such as fibreboard) to prevent “burnouts” from hot asphalt]
• Will not retain nails (requires screws and plates)
• Dimensional instability may result from improper curing at the factory.

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