Book - School of Science and Technology

Heat losses 29WallsRoofFloorWindows210 mm brickwork, unplastered.19 mm asphalt on 75 mm screed and 150 mm concrete, unplastered.Solid in situ concrete on earth.Single glazing in metal frames without a thermal break.SurfaceArea (A)(m 2 )U(W/m 2 K)AU(W/K)Floor ˆ 14.5 8.5 ˆ 1236.0 8.5 ˆ 51 174 0.58 ˆ 101Roof ˆ 6.0 8.5 ˆ 51 2.16 ˆ 110Windows ˆ 12.0 2.0 ˆ 24 5.7 ˆ 137Walls ˆ 48.5 4.0 ˆ 194less windows ˆ 24 170 2.32 ˆ 394419 742Thus, the conduction loss, air to air, is 742 22 ˆ 16:32 kW and (AU)/A ˆ742/419 ˆ 1:8 W/m 2 K.Building insulationConsideration of thermal insulation has now come to be regarded as an essential routineduring the design process for a new building and a matter for earnest consideration inrefurbishment or change of use of any building constructed more than a decade ago.Insulating materials tend to be porous by nature and hence are structurally weak: they areTable 2.3 Thermal insulating materials for buildingsMaterialSpecific moss(density)(kg/m 3 )Specific heatcapacity(kJ/kg K)Thermalconductivity (k)(W/m K)Concrete block, aerated a 700 1.0 0.27Concrete block, aerated a 500 1.0 0.18Concrete block, lightweight 600 1.0 0.19Fibreboard 300 0.7 0.06Glass fibre (quilt or mat) 12 0.84 0.04Glass fibre (slab) 25 1.0 0.035Mineral fibre (blown) 12 0.84 0.04Mineral fibre (mat) 50 1.0 0.037Mineral fibre (slab) 30 1.0 0.033Phenolic foam (board) 30 1.38 0.018Polystyrene (expanded, slab) 15 1.38 0.035Polystyrene (extruded, slab) 15 1.4 0.025Polyurethane, CFC blown (board) 30 1.4 0.019Polyurethane, PHA blown (board) 30 1.4 0.021Urea formaldehyde (foam) b 10 1.4 0.031Vermiculite (granules) 100 0.83 0.065NotesThe values quoted here do not allow for any heat bridging. See text for approximate practical adjustments.a Protected, moisture content 3% by volume.b For use only where there is a continuous barrier which will minimise the passage of fumes into the occupied space.