Cavity wall insulation vs. external wall insulation is an age-old argument that leaves people wondering as to what the best option is. It started as cavity wall insulation being solely for people who have houses with cavities (obviously), and external wall insulation was for people with solid wall houses.

Cavity wall insulation dominated the market as being the primary solution because most people had houses with a cavity wall. However, these days the world has gone energy-saving mad (which is a good thing!) and people want extra-extra super-insulated houses without having to spend too much money.

There’s a lot to be said for both types of insulation, and ultimately the decision will come down to what is right for your budget and your particular property. With cavity wall insulation’s history of poor installation and resulting damp, people tend to become concerned with the risks involved with this type of insulation. Nevertheless, it’s important to remember that both types of insulation have the potential to go wrong and need to be installed by qualified professionals.

We’ve put together a quick guide on the advantages and disadvantages of both cavity and external wall insulation.

Advantages of Cavity Wall Insulation

  • Will not affect the external appearance of the property
  • Does not require the loss of internal space
  • Cavity wall insulation reduces your energy bills – it can save you £100-200 a year on your heating bills.
  • Keeps your house warmer in the winter
  • Reduces your carbon footprint
  • Very quick and easy to install
  • Cheaper than external wall insulation

Disadvantages of Cavity Wall Insulation

  • Risk of poor installation from underqualified installers
  • Has been known to trap moisture and cause damp when poorly installed
  • Restriction on the amount of insulation that can be installed (dependent upon the size of the cavity) therefore less effective than EWI
  • Not suitable for all buildings (i.e. solid walls).

Advantages of External Wall Insulation

  • Requires no internal space
  • Can massively improve the look of a property due to the decorative topcoat
  • No restriction as to how much insulation you can install (you can get up to 200mm+)
  • Therefore no restriction on how much energy you can save
  • Certain insulation materials (i.e. Rockwool) have soundproofing capabilities as an added advantage
  • Regulates the thermal comfort of the home
  • Unlikely to cause damp and condensation when installing properly
  • No thermal bridges – continuous insulation
  • Prolongs the life of the building by protecting its exterior walls
  • Can increase the value of the property in terms of its energy efficiency and external appearance
  • Low maintenance
  • Virtually any property can have it installed

Disadvantages of External Wall Insulation

  • More expensive than cavity wall insulation due to the number of materials required and the higher level of skill needed to install it
  • Requires skill to install it to ensure it is safe and won’t cause problems, so you need to be careful of who you hire
  • Can be difficult to get planning permission for older properties, as it creates a completely new exterior
  • It may need occasional maintenance to ensure the render topcoat looks fresh

Should You Switch From CWI to EWI?

If you already have cavity wall insulation installed and it’s not as effective as you would like it to be, then you can certainly install external wall insulation as well. Essentially by doing this, you’ll be achieving two layers of insulation, and any thermal bridges within the existing cavity wall insulation will be erased by the EWI. Cavity wall insulation and external wall insulation together will achieve maximum effectiveness.

The downside is that you can’t have one without the other. Trying to install EWI onto an empty cavity wall will achieve very little, as the air within the cavity will just be heated up before escaping.

What it comes down to is what’s best for your property and your budget. If you’re looking for a bit more advice on the subject then give our technical team a call and we can talk you through the options for your home.

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