You may know that all new and replacement windows now have to comply with current Building Regulations for insulation performance values and those that do not meet standards could result in fines for householders! Windows and doors installed under the new regulations must have a Certificate of Compliance by law and this certificate has to be produced as part of any future house sale. Those who do not use a FENSA registered installer will have to call in a Building Inspector to obtain a Certificate of Compliance - at their own cost.