Frequently asked questions

Below you will find answers to questions we are frequently asked regarding timber sash windows, casements and doors. If you have your own questions that are not answered here, please feel free to contact us.

What are the current regulations regarding replacing windows/doors?  If you replace your windows and doors, they must comply with a given minimum standard of energy management i.e. heat loss. This is part of the Governments obligation to the international agreement on reducing greenhouse gasses.

What is document L & what is a “U” value?  All new or replacement box sash windows, installed after April 2002, have to comply with Document L, which is a considerable toughening up of the Government's glazing regulations.Document L deals with the heat saving properties, the "u-value", of windows.   The better heat saving properties, the lower the u-value.  U-value is measured by the rate of heat loss from the warm inside of the house through the window/door to the outside, if it’s colder there.  The lower the U-value, the smaller the loss of heat, i.e. better energy management.

So what is this standard for my house?  Any replacement window or door must not have a “U-value” which exceeds 2.0.  In any new build, which includes conservatories, the U-value must not exceed 1.8.  Many of our sash windows are 1.37 which is much U-value better than the minimum required for even new builds.

How can I be sure that my new or replacement windows do comply?  You can make sure you deal with an accredited window supplier.  Suppliers that comply with the new regulations are accredited by the National Physical Laboratory.  Your windows will be supplied with certificates that authenticate compliance.

How is the system policed?  Every installation must be registered with the Local Authority. The installation company can either do this themselves or join an industry organisation called FENSA which does this for them.

How does FENSA know what’s going on at my house?  The installer must inform FENSA, who then make random checks from a list of jobs supplied by the installer, to monitor the U-values of its typical work.

What’s the practical benefits to me?

• Peace of mind
• Windows/doors that are guaranteed to keep you comfortable, warm, and minimise your fuel bills