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Centre Pane Test

A 'Centre Pane of 1.2' (1.2W/m²K) provided compliance for all replacement windows in the 2006 regulations.

This option is now restricted to where there is a need to maintain the external appearance of the building. In these circumstances the replacement windows should meet a centre pane of 1.2W/m²K.

Glass centre pane
Centre Pane < 1.2W/m²K

For replacement windows only it is possible to claim compliance with Part L1B and L2B by certifying or proving that the window is glazed with glazing with a ‘centre of glass’ U value < 1.2 irrespective of frame type.

This only applies to replacement windows and doors where there is a need to maintain the external appearance of the building.