Q4. A roof is normally exposed to the thermal environment, is composed of the following components,

Tiles for roof = 20 mm.

Cement mortar = 60 mm.

Concrete (ballast) = 130 mm.

If the required U-value for roofs is = 0.62 W/m. sq.-degree C. and the heat flow is downwards.

i. Calculate the U-value of the existing roof.

ii. Calculate the required thick of mineral wool, if its thermal conductivity is 0.042 W/m-C

Given that the thermal conductivity of the roof tiles is 0.885 W/m-C, the cement mortar is 0.5W/m-C and the

concrete slab is 1.5 W/m-C. Assume the thermal resistance of External is 0.059 m²-°C/W, the roof tiles is 0.0226 m²-

°C/W, the cement mortar is 0.0400 m²-°C/W, concrete is 0.1000 m²-°C/W, internal is 0.154 m²-°C/W.