Energy Saving Grants | Government Grants for Energy Efficiency

Internal or External Wall Insulation | Which One is Better?

If your house features solid rather than cavity walls, it’s likely experiencing higher heat loss, making it beneficial to invest in wall insulation. Although insulating concrete walls is more costly than insulating cavity walls, grants are available to help cover the expenses.

You can choose between internal or external wall insulation for solid walls. Both options offer comparable energy savings but have distinct pros and cons. Whether you opt for internal or external wall insulation, addressing any issues related to rising or penetrating dampness in the walls before starting the insulation process is crucial. 

Deciding between these two options depends on various factors. Continue reading this article to learn which one you should choose. 

What Is Internal Wall Insulation?

Internal insulation for a solid wall involves adding a layer of insulation material to the inside surfaces of the walls. This process typically includes fixing a layer of insulating material to the wall, which is then covered with plasterboard or a similar finish. The main goal of internal insulation on a solid wall is to reduce heat loss, thereby improving the home’s thermal efficiency.

Advantages Of Internal Insulation Of Solid Walls

One of the key advantages of internal insulation on a solid wall is that it doesn’t alter the external appearance of the building, making it a preferred choice for homes in conservation areas or for those with aesthetic restrictions. 

However, it slightly reduces the internal floor space and requires removing and reinstalling skirting boards, door frames, and fixtures. This method is often considered more disruptive than external insulation but can be more cost-effective and easier to install in some cases.

Advantages Of Internal Insulation Of Solid Walls

  • Internal insulation tends to be less expensive than external options, allowing grant funds to cover a more significant portion.
  • The external appearance of your house remains intact, which is crucial for homes with historical significance. 
  • This aspect makes internal insulation appropriate for properties in Conservation Areas where exterior modifications are often restricted.
  • Installation is simpler, often eliminating the need for scaffolding.
  • It’s a more viable option for individual units in multi-residence buildings like flats or maisonettes, where applying external insulation to a single unit is not feasible.

Disadvantages of Internal Wall Insulation:

  • Internal insulation can reduce the available room space, potentially bringing in the walls by up to 4 inches.
  • The installation process can be invasive, requiring the temporary removal and reinstallation of items such as light switches, skirting boards, radiators, and carpets. 
  • Moreover, the work is carried out inside your home, which can be disruptive.
  • There’s a risk of concealing internal period features of the home, which might be significant for some properties.

Choose internal wall insulation of solid wall if:

  • You’re planning to insulate just one or two rooms in your home.
  • External Wall Insulation (EWI) isn’t feasible due to planning restrictions or physical constraints, such as properties that border public pathways or roads.
  • Your internal walls are relatively featureless, with minimal fixtures like radiators or light switches.
  • You’re okay with some level of disruption inside your house during the installation process.
  • Additional weather protection is optional for you.
  • You’re comfortable with the prospect of slightly reducing the size of your rooms.
  • You’re willing to allocate a budget for post-installation redecoration.

Internal Or External Wall Insulation – The Differences

Feature External Wall Insulation Internal Wall Insulation
Disruption in Home Minimal, as work is external. More, requiring access to internal walls.
Rewiring Not needed; some ancillary work may be needed for external fixtures. Necessary for electrical sockets and light switches.
Wall Coverage Complete coverage of walls. Partial coverage possible, may result in cold spots.
Living Space Impact None. Reduces internal space; may affect character features.
Condensation Helps in preventing damp and condensation. Requires a vapour control layer, which can be compromised by wall alterations.
Cost Generally less expensive. Generally more expensive due to redecorating.
Other Considerations May require planning permission. Reduces room sizes.
Energy Saving Detached: 1,870kg CO2/year, Semi-Detached: 1,120kg CO2/year, Mid Terrace: 690kg CO2/year. Same as EWI.
Cost Saving Detached: £425, Semi-Detached: £255, Mid Terrace: £160. Same as EWI.

Final Thoughts

Unless you’re renovating a house extensively, down to the bare bricks, external wall insulation is generally preferred over internal insulation. This isn’t to say that internal insulation isn’t practical – both methods can significantly reduce energy bills. However, because of spatial considerations, achieving higher thermal efficiency is typically more feasible with external wall insulation.

Read more: New Build Cavity Wall Insulation Regulations in 2023

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