Double Glazing With regard to double glazing, we supply and fit double-glazed units predominantly into new frames for building companies. The units we install are a ‘Kite marked’ unit and they have a dual-seal edge which is a secondary seal which prevents water ingress and it is a lot better than the ‘normal’ double glazed unit which has a single seal. As from the 1st of April 2002 all double glazed units which we install into new-build are one-leaf, Pilkington ‘K’ Glass to conform with the new building regulations which came into force on that date, under the heading ‘Document L’. Whilst on the subject of double glazing we are also a FENSA registered company. and on completion of all double glazed units for both building contractors and private householders etc we issue a certificate to state that the installation has been completed satisfactorily to 'Document L' Building Regulations. It should be noted that not all companies are FENSA registered even though it is now a legal requirement.