If you are currently building a house in the UK, you will need to install the right windows for it. When looking for window varieties, why not choose Double Glazed Sash Windows? Since codes on building and windows installation are followed strictly in the UK, it is important that you find reputable window installers. A company which has records at FENSA or Fenestration Self-Assessment Scheme gives you the assurance that they follow strict building codes. FENSA also certifies that these businesses uphold strict measures in environment protection. Therefore, you need to make sure that the company is FENSA-certified, in order to get the best services.