Weighing the material options

By Rockford Boyer, B. Arch. Sc.
Understanding the major material types in exterior insulation sheathing is important for design professionals.

Stone or mineral wool
In the manufacture of stone or mineral wool, raw material and coke residue are fed from the top of the cupola furnace. The melt runs out of the bottom of the furnace and onto the spinning machine, where the fibres are spun. Minor amounts of binder and oil are added, and the wool is collected on a belt conveyor in the spinning chamber. Structure and density are adjusted before the material enters the curing oven. (These properties are maintained after the binder has been cured.) The cured wool then proceeds to the cutting saws and packing equipment or is led to off-line equipment for special treatment.

Extruded polystyrene (XPS) foam begins as solid resin granules, which are fed into an extruder where they are melted and critical additives are mixed with the resulting viscous fluid. A blowing agent is then injected to make the mixture ‘foamable.’ Under carefully controlled heat and pressure conditions, the foamable mixture is forced through a die, at which point foaming and shaping occurs. The rigid foam is then trimmed to the final product dimensions.

Polyiso insulation is a closed-cell, thermoset plastic foam insulation that is made in board form. Through a continuous lamination technique, liquid raw objects become light but strong; they then expand and are placed between engineered facers.

For more on exterior sheathing, click here.

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