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# Long description

This diagram shows a labelled ceiling supported from above by a number of labelled ceiling joists. The ceiling joists have a vertical thickness of about 100 millimetres. The ceiling is seen in section from the side. Different insulation thicknesses are shown in the loft above the ceiling with their U-values shown above in units of watts per square metre per kelvin. Vertical orange arrows of different thicknesses also indicate the relative heat losses. At the left an uninsulated ceiling has a broad orange arrow and has a U-value of 1.9. To the right a layer of insulation 25 millimetres thick is shown with a thinner orange arrow and a U-value of 1.0. To the right of this a layer of insulation 80 millimetres thick is shown with a thinner heat loss arrow and a U-value of 0.48. To the right of this a double layer of insulation is shown. The bottom layer is 100 millimetres thick and reaches to the top of the ceiling joist. A further layer 150 millimetres thick covers both the first layer and top of the ceiling joist. It has a thin heat loss arrow and a U-value of 0.16. At the far right a similar arrangement is shown but with the thickness of the top layer increased to 200 millimetres. This has a thin heat loss arrow and a U-value of 0.14.