Understanding the thermal performance of your glass rooflight

Glass rooflights with high-energy efficiency will ensure that heat loss is reduced in your home, increasing comfort levels whilst reducing costs.

Thermal performance is calculated using a measurement called a U-value, which measures the amount of heat loss through the glass rooflight. The best rooflight suppliers will be experienced at dealing with U-values and be able to carry out in house 2D thermal modelling to determine thermal performance for any design specification.

Note that building regulations require a “whole rooflight” U-value; therefore manufacturers that only quote the glass performance or ‘centre pane’ U-value are giving a false perception of their products performance.

Providing overall U-values is the very least you should expect, but ideally your supplier will be able to back this up by providing calculations for your specific rooflight, not just generic documentation for a certain specification of glass. Ask for thermal reports that clearly break down the various values; these are invaluable when dealing with Building Control or architects.

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