Effect of Insulating Materials on Heat Transfer Through Exterior Walls

Effects different insulating materials have on heat transfer through exterior house walls Tim Doot and Sabin Gautam

Wall Detail

Thermal Resistance of wall components • Gypsum Sheathing - (13 mm) - 0.079 K·m2/W • Gypsum Wallboard - (50 mm) - 0.085 K·m2/W • Brick Veneer - (100 mm) - 0.66 K·m2/W Insulation materials • Fiberglass/cellulose insulation - (90 mm)- 11.2 K·m2/W • Mineral Wool insulation - (90 mm) - 10.85 K·m2/W • Sprayed foam insulation - (90 mm) - 15.75 -> 22.75 K·m2/W

Total heat transfer Equation • Q = -A·(ΔT/Rtot) • Toutside = -7°C • Tinside = 20°C • Thermal Resistance (R) = L/K·A • Rtot = Rbrick + Rsheathing +Rinsulation +Rwallboard • Rtot = 0.66 K·m2/W + 0.079 K·m2/W + Rinsulation + 0.085 K·m2/W • Rinsulation (Fiberglass)= 12.024 K·m2/W • Rinsulation (Mineral Wool)=11.674 K·m2/W • Rinsulation (Sprayed Foam)=16.574 -> 23.574 K·m2/W

Heat transfer for different insulations • Fiberglass/Cellulose • Q = 27 K/12.024 K·m2/W • Q = 2.25 W/m2 • Mineral Wool • Q = 27 K/11.674 K·m2/W • Q = 2.31 W/m2 • Sprayed Foam • Q = 27 K/(16.574 K·m2/W) –> 27/(23.574 K·m2/W) • Q = 1.63 -> 1.15 W/m2

Conclusions • The calculations show that the sprayed foam insulation can be up to twice as effective as the fiberglass insulation in reducing heat transfer through an exterior house wall • It would be worth it to spend the extra 30% in costs to install the sprayed foam insulation and save on energy costs than to install the fiberglass insulation for a reduced initial cost

References • http://www.gobrick.com/BIA/technotes/t28_files/image001.jpg • http://www.american-sprayfoam.com/residental • http://www.fao.org/docrep/006/y5013e/y5013e08.htm

Effect of Insulating Materials on Heat Transfer Through Exterior Walls