It is important for houses in the UK to have top quality windows installation, so as to give the house proper insulation. When you are on the lookout for several window types, why not choose double glazed sash windows? Then again, you need to find a company that judiciously follows UK building codes. A company which has records at FENSA or Fenestration Self-Assessment Scheme assures you that they follow strict building codes. If you are environmentally concerned, a FENSA registered company certifies their procedures as perfectly safe for the environment. When intending to put up windows, you need to go for a company that is FENSA registered.