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(d) An external wall of a building is composed of 105 mm brick (k = 0.84); 65 mm
cavity (Rcav = 0.18); 105 mm lightweight concrete block (k = 0.20); 15 mm
lightweight plaster (k = 0.16). Take (internal resistance) Rsi as 0.12 and (external
resistance ) Rse as 0.05.
(i) Calculate the thermal transmittance (U value) of the following construction:
L/K = R for lightweight concrete blocks and bricks
Total resistivity (Rtot)
U = 1/(Rtot)
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[4 marks]
(e) Discuss the role of a cavity in a wall and its deficiencies in reducing heat
transmittance.
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[4 marks]
Total 20 marks
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02265020/SPEC 2015
