In the first of a series of blogs to help you with a home retrofit we start thinking about replacing windows or doors.

Windows can make a room feel too cold….. or too hot. 

  • The U value of the whole window (Uw) is a measure of total heat loss through the glazing, the frame and the perimeter of the glass. 
  • Uw depends on the size and shape of each window and the amount of glazing relative to the frame. 
  • The g value tells you how much heat from the sun can get in (the lower the better if you have an overheating issue on sunny days) 

Think about the seals to prevent draughts. Some windows and doors have better seals than others. Bifold doors and sash windows are particularly prone to failure of seals over time. Also think about heat loss around the frame when the window is installed. There may be a gap you can’t see between window and reveal (often hidden by trims and finishes). This can lose more heat than the whole window, so make sure your windows are installed properly! These hidden gaps can also cause mould growth around the window.   

If a room is overheating because of excessive solar gain through a window, consider external shading (it is much more effective than internal blinds or curtains). South facing windows may benefit from a brise soleil, while west facing windows may benefit more from external blinds or shutters. Think about this before you buy your windows. It may affect the windows you choose, which way they open, and how you control your external blinds or shutters. 

Think about your wall insulation before you buy windows or decide on shading options – are you planning to insulate your walls externally or internally, now or in the future? Think about this before selecting windows and installing them. 

If you’re in need of a whole house plan to allow you to consider all of the home improvements you’d like to make and how they fit together, click here to find out how we can help.


For choosing windows, see our free recorded webinar: Eco-Retrofit: Focus on Windows and Doors Unit 1: Choosing doors and windows – Webinar recording – YouTube 

For installing windows, see our free recorded webinar: Eco-Retrofit: Focus on Windows and Doors Unit 2: Window installation – Webinar recording – YouTube