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Q&As
Insulation of an existing bungalow?
My home's exterior walls have had cavity wall insulation but I do not know how effective it is. Similarly double glazed upvc windows are fitted.
How can I determine the insulation of the walls and windows?
Also what is the best way of improving the U value of the walls?
One Answer
Cavity uninsulated is roughly 1.5W/m2K.
Cavity wall with insulation injected is about 0.55W/m2K
(Modern regs for new build 0.3W/m2K)
So you can see that Cavity wall insulation (CWI) takes you most of the way to modern regs.
However… the cavity had a function (keeping the building dry) and in many cases CWI has led to damp, and much higher heat transfer (higher u-values). So the condition of the exterior skin is vital. Sometimes CWI is not properly installed and obstructions can lead to uninsulated areas, or gaps at the top. Thermal imaging may be useful to reveal these. In situ u-value testing would be more accurate than using the modelled figures quoted above.
If the exterior surface is not significant (visually), then EWI could be added to reduce the value below 0.3Wm2K.
The u-value of the windows is dependent on the type of glass, thickness, fill, coatings (if any) and the gap between the 2 panes. Early double glazing would merit replacement but not later – as embodied energy is rarely repaid over the life of the windows. If ever replacing, use timber as it is natural, non-polluting, lasts longer, is repairable, etc.