Interlocking extruded polystyrene panels are available with a decorative cementitious surfacing to provide an inverted roof which is lightweight and will need additional loading. The interlock ensures safety against wind forces within limits prescribed by the manufacturers. A special grade of panel is available with a reinforced decorative cementitious surfacing for pedestrian terrace decks.
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Composite boards consist of insulation products which individually are suitable for roofing. The long term bond strength between the materials should be at least as strong as the de-lamination strength of the weakest individual component. The composite board should be free from warping, bowing and be dimensionally stable both during application and in service.
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Phenolic foam is similar in structure to rigid urethane foams, and needs to conform to internationally agreed ODP levels. An extremely small cell size is possible, and leads to an improved λ value. The cell walls tend to be friable, which makes the foam rather vulnerable to damage but formulations are rapidly improving. The advantage of phenolic foam is a greater resistance to high temperature than other foams, and the possibility of improved performance in a fire. In other respects phenolic foam is similar to rigid urethane.
