The 900mm x 900mm VELUX ZCU 0015 150mm PVC Extension Kerb for Flat Roof Windows (with flange) has been designed to work with the VELUX C-U, the kerb has been designed for use with warm roofs and flat windows. This kerb will provide your roof with additional height. The flange adds an extra layer of protection/collar around the base. The new generation of VELUX glass rooflights features 52% more natural daylight, reduced height, a new state of the art design that makes this range sit flush with your roof, discreet black corner keys for a smoother finish and new installation screws and prepared for craning. VELUX provide a 10-year guarantee on roof windows and a 5-year guarantee on electrics. Features & Benefits Comes with flange Designed to work with VELUX C-U Provides your roof with additional height Part of the new generation of rooflights