When building your Blade, you have to select between double glazed units with Argon gas (Double-A) or triple glazed units with Krypton gas (Triple-K) coupled with the highest performing soft coat low-e glass available.

rooflight u-values simplified

The U-value is the measurement of heat lost through a roof window. The lower the U-value, the better the rooflight is at keeping heat in.

There are three ways to measure the heat loss of a flat roof window as explained below – Ug, Uw and Ud. The glass Ug-value tends to be the lowest U-value and many rooflight companies only quote this figure which in our eyes is essentially cheating. Building regulations inspectors are not concerned with the rooflight glass U-values, they are more interested in ‘combined product’ U-values.

Clients should also bear in mind that triple glazed rooflights are not necessarily better than double glazed rooflights for the UK climate when you factor in ‘solar gain’ which is free heat harvested from the sun in the spring, autumn and winter.

glass centre pane u-value (ug)

Heat lost through the middle of the glass is called the Ug-Value. This measurement remains the same irrespective of the rooflight size.

combined glass and frame (uw)

The Uw value measures heat lost through both the aluminium rooflight frame and glass combined.

combined glass, frame and kerb (ud)

This is the combined ‘developed area’ heat loss measurement of the glass, frame and insulated kerb combined.

blade rooflight u-values

Double-A centre pane Ug-value is 1.0 w/m2k
Triple-K centre pane Ug-value is 0.4 w/m2k

Double-A glazing and frame combined Uw-value from 1.2 w/m2k
Triple-K glazing and frame combined Uw-value from 0.6 w/m2k

Double-A glazing, frame and kerb combined Ud-value from 1.1 w/m2k
Triple-K glazing, frame and kerb combined Ud-value from 0.4 w/m2k

All Blade rooflights fully comply with building regulations minimum heat loss requirements of 1.6 w/m2k for domestic installations and from 1.8 w/m2k for commercial installations. Double-A Blades are double glazed with argon gas and Triple-K Blades are triple glazed with Krypton gas, both with soft coat low-e coatings and warm edge spacer bars.