Home > Grants & Advice > Insulation Advice > External Wall Insulation Advice > External Wall Insulation Vs Internal Wall Insulation

External Wall Insulation Vs Internal Wall Insulation

If you are interested in funded cavity wall insulation, click your area to see what's available:

External Wall Insulation (EWI) is insulation fitted to the outside of your house. It saves energy, reduces fuel costs and can add value to your house.

Internal Wall Insulation (IWI) is insulation fitted on the inside of your walls. It also saves energy and reduces fuel costs

The Main Considerations:

EWI will improve the look of your house often adding financial value.
IWI is cheaper on its own than EWI, but with the added costs of redecorating and replacing any fittings, skirting boards or other elements, it normally ends up costing a lot more.
For IWI, rewiring will be necessary, light switches have to be moved and decorative features like skirting boards can cause problems.

When to have External Wall Insulation:

If you want to improve or enhance the look of the outside of your property
If you want to minimise disruption during the install
If you want to weather proof your property
If you want to increase noise insulation

When to have Internal Wall Insulation:

If you only want to insulate one or two rooms
If you cannot have EWI due to planning constraints or access requirements (e.g. the property has no external space surrounding it and infringes onto a public walkway or road)
If your internal walls have little or no features (e.g. radiators, light switches, etc)
If you don’t mind a bit of disruption in the house
If you don’t need extra weather protection
If you don’t mind reducing the size of your rooms
If you are prepared to pay more for redecorating

Features	External Wall Insulation	Internal Wall Insulation
Disruption in the home	Little disruption as all work is on the outside of the property.	More disruptive as access will be required to treat internal walls.
Rewiring	No rewiring needed. Although some enabling work may be required (e.g. repositioning telephone cables, satellite dishes, etc)	Electrical sockets and light switches will need to be moved and reconnected.
Wall Coverage	Total wall coverage.	It is not always possible to cover all of the walls, so there may be cold spots.
Living space impact	None.	Reduces internal living space, character features like skirting boards, door frames and picture rails may also cause problems.
Condensation	Helps prevent damp and condensation.	Requires a vapour control layer which can be made vulnerable if a resident puts a nail in the wall without knowing.
Cost	Normally less expensive.	Normally more expensive due to redecorating.
Other Considerations	May need planning permission.	Reduces the size of rooms.
Energy Saving	Detached House - 1,870kg CO2/year Semi Detached House - 1,120kg CO2/year Mid Terrace House - 690kgCO2/year	Detached House - 1,870kg CO2/year Semi Detached House - 1,120kg CO2/year Mid Terrace House - 690kgCO2/year
Cost Saving	Detached House - £425 Semi Detached House - £255 Mid Terrace House - £160	Detached House - £425 Semi Detached House - £255 Mid Terrace House - £160