## Determining the thickness of insulation for roofs

Figure 4.1 illustrates three common roof types, and Table 4.6 gives the base thickness of insulation for these roofs.

Because the base thickness may not be the minimum, the reductions in heat flow due to other elements of the construction must be considered, and further corrections may be made to reduce the base thickness to give the minimum thickness. The amounts by which the base thickness may be reduced are given in Table 4.7.

 MMMMMiWiiMWM 11 111

(b) Insulation laid between and over joists or rafters

(b) Insulation laid between and over joists or rafters

Fig. 4.1 Three common roof types.

(c) Continuous layer of insulation over a structural base

Fig. 4.1 Three common roof types.

 Design Thermal conductivity of the insulation material, W/mK 0.020 0.025 0.030 0.035 0.040 0.045 0.050 U-value W/m2K Base thickness of insulation layer, mm Insulation laid between ceiling joists or rafters 0.15 371 464 557 649 742 835 928 0.20 180 224 269 314 359 404 449 0.25 118 148 178 207 237 266 296 0.30 92 110 132 154 176 198 220 0.35 77 91 105 122 140 157 175 0.40 67 78 90 101 116 130 145 Insulation laid between and over joists or rafters 0.15 161 188 217 247 277 307 338 0.20 128 147 167 188 210 232 255 0.25 108 122 137 153 170 187 205 0.30 92 105 117 130 143 157 172 0.35 77 91 103 113 124 136 148 0.40 67 78 90 101 110 120 130 Continuous layer of insulation 0.15 131 163 196 228 261 294 326 0.20 97 122 146 170 194 219 243 0.25 77 97 116 135 154 174 193 0.30 64 80 96 112 128 144 160 0.35 54 68 82 95 109 122 136 0.40 47 59 71 83 94 106 118
 Concrete Thermal conductivity of the insulation material, W/mK 0.020 0.025 0.030 0.035 0.040 0.045 0.050 slab density kg/m3 Reduction (mm) in the base thickness of the insulation, for each 100 mm thickness of the concrete slab 600 10 13 15 18 20 23 25 800 7 9 11 13 14 16 18 1100 5 6 8 9 10 11 13 1300 4 5 6 7 8 9 10 1700 2 2 3 3 4 4 5 2100 1 2 2 2 3 3 3 Various materials and Reduction in the base thickness of the insulation components mm 10 mm plasterboard 1 2 2 2 3 3 3 13 mm plasterboard 2 2 2 3 3 4 4 13 mm sarking board 2 2 3 3 4 4 5 12 mm calcium 1 2 2 2 3 3 4 silicate liner board Roof space (pitched) 4 5 6 7 8 9 10 Roof space (flat) 3 4 5 6 6 7 8 19 mm roof tiles 0 1 1 1 1 1 1 19 mm asphalt 1 1 1 1 2 2 2 (or 3 layers of felt) 50 mm screed 2 3 4 4 5 5 6