When it comes to improving the energy efficiency of solid wall homes in the UK, insulation is one of the most impactful upgrades you can make. Approximately one-third of all heat lost in an uninsulated home escapes through the walls. For homes built before the 1920s, which typically have solid walls rather than cavity walls, the solution is either Internal Wall Insulation (IWI) or External Wall Insulation (EWI).
External Wall Insulation (EWI)
EWI involves fixing a layer of insulation material to the outside of your home and covering it with a special render or cladding.
Pros: Does not reduce internal floor space; improves the outer appearance of the home; disrupts household life less during installation.
Cons: Generally more expensive; may require planning permission; changes the look of the property.
Internal Wall Insulation (IWI)
IWI involves fitting rigid insulation boards to the inside of your external walls, or building a stud wall filled with mineral wool fibre.
Pros: Cheaper than EWI; no planning permission required; maintains the external character of the building (important for listed buildings).
Cons: Slightly reduces floor space; requires re-decorating and moving radiators/skirting boards.
Which is Right for You?
If you have a limited budget or live in a conservation area, IWI is often the better choice. If you want to minimize disruption inside your home and have the budget, EWI is a fantastic option. Under the ECO4 scheme, you may qualify for funding for either measure depending on your property type and eligibility.
