How can I measure and improve my home’s U-value?

My property has cavity wall insulation (CWI) and double glazed PVCU windows, however I don’t know how energy efficient they are. How can I determine the insulating capacity of the walls and windows and how can I improve my property’s U-value with these things considered?

U-values are a measure of thermal performance, where lower figures indicate a structural element loses less heat. Walls with CWI achieve about 0.55 W/M2K and Building Regulations for new builds are 0.3 W/M2K; so, you can see that your CWI takes you most of the way to modern standards.

However, the cavity in your walls has a function (to keep the building dry) and in many cases adding CWI leads to damp, much higher heat transfer and subsequently worse U-values. is means that the condition of the exterior brick skin is vital. If CWI isn’t properly installed, obstructions can lead to uninsulated areas and gaps in the wall. You can find these with thermal imaging. I suggest using in-situ U-value testing instead of referring to the modelled figures quoted above. If the external surface is not significant (visually), then you could add exterior wall insulation (EWI) to reduce the result below 0.3 W/M2K.

e U-value of the windows is dependent on the type of glass, thickness, fill, coatings (if any) and the gap between the two panes. Early double glazing would merit replacement, however recently installed double glazing should be retained – as the embodied energy of swapping this out is rarely repaid over the life of the windows. If ever replacing, I’d recommend using units with timber frames as this material is non-polluting and repairable.