Glass Roof U Value

Determine the thickness of the insulation layer above the joists required to achieve a u value of 0 20 w m2k for the roof construction shown below.

Glass roof u value.

Technically u values are calculated as the amount of heat lost through one square meter of glass for every degree difference in temperature either side of the glass. In descending order these are typical u values for glass. Double glazing with 16 20mm gap 3 0. Triple glazing with 16 20mm gap 2 2.

Example of how u values work. For example a building with material with an r value of r 11 converts to an u value of 0 09 1 r or 1 11 0 09. This glass specification will produce a glass unit with ug value of 1 0 1 1 w m 2 k. Reference table for u values u value is the coefficient of transmission i e the transmission of heat through the materials which compose the building s envelope or outer shell.

So for example if the temperature difference on a typical cold day was 15 degrees then the amount of heat loss would be 15x6 90 watts per square metre. There are various ways of improving the uw value of an installation. U value has an inverse relationship to r value. Obviously improving the individual u factors in the calculation will improve the overall thermal performance.

The u value of a single sheet of glass as found in a traditional window pane is 6 0w m 2 k which means that for every degree of temperature difference between the outside and the inside a square metre of the glazing would lose 6 watts.