Fensa FENSA stands for the Fenestration Self-Assessment Scheme. It has been set up by the Glass and Glazing Federation (GGF), with Government approval, in response to the new Building Regulations for England and Wales. From 1 April 2002, all replacement glazing in dwellings will come within the scope of the Building Regulations. From then on, anyone who installs replacement windows or doors will have to comply with improved thermal performance standards. When having their windows and doors replaced from this date homeowners must ensure that they get a certificate form Local Authority Building Control or have the work completed by a FENSA Registered Company. One of the main reasons for this change to the Building Regulations is the need to reduce energy loss.