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Specification options: thermal insulation
Cellular plastics: pitched roofs over, between or under rafters 
Expanded polystyrene to BS EN 13163, 0.036 W/m2K, 190mm thick, U–value 0.189 W/m2K32-35
Rigid polyisocyanurate to BS EN 13165 with integral foil backing, 0.023 W/m2K, 125mm thick, U–value 0.184 W/m2K19.50-21.50
Rigid urethane to BS EN 13165 with integral foil backing, 0.023 W/m2K, 130mm thick, U–value 0.177 W/m2K22-28
Rigid phenolic foam to BS EN 13166 with integral foil backing, 0.021 W/m2K, 100mm thick, U–value 0.210 W/m2K23.50-26
Plant and animal based insulants: laid in loft space 
Cellulose fibre loose insulation, 0.040 W/m2K, 210mm thick to allow 5% settlement, U–value 0.20 W/m2K5.50 - 7.50
Sheep's wool insulation slabs, 0.390 W/m2K, 200mm thick, U–value 0.195 W/m2K18-20
Mineral fibre: laid in loft space 
Stone wool quilt to BS EN 13162, 0.044 W/m2K, 200mm thick, U–value 0.22 W/m2K7.90 - 8.70
Glass wool quilt to BS EN 13162, 0.044 W/m2K, 200mm thick, U–value 0.22 W/m2K6.40 - 7.10
Glass wool quilt to BS EN 13162, 0.044 W/m2K, 200mm thick, ready cut to fit roof joists, U–value 0.22 W/m2K12-14.80
Table notes. Costs are for materials only. Consideration of construction, fixings design, location, as well as overall energy strategy is required for a direct comparison of options. These may vary considerably. Consideration of functional requirements other than thermal insulation such as loading, acoustics and fire resistance may override economic evaluation based on thermal properties. Cost are built up from common insulation thicknesses. Use of non–standard thickness may be more costly. For large quantities discounts may be negotiated.