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  • Big reduction in heating bills
  • Can last a very long time

What it is 

Insulation can be added to the inside or outside surface of your walls to help keep your home warm and cut your heating bills. 

If your walls are not suitable for standard cavity wall insulation, then it may be possible to fit solid wall insulation instead. A layer of insulation material is fixed either to the inside surface of your walls (internal wall insulation) or to the outside (external wall insulation). The insulation layer is then covered with another layer to protect the insulation. This covering layer will also allow decorating if on the inside, or will keep the rain out if on the outside. 

Is it right for me? 

If your house was built before the 1920s, then it is quite likely to have solid walls. Some newer houses were built without a standard cavity, in which case solid wall insulation may be the best option. 

Before about 1920, most houses in the UK were built with solid walls – that is, the outside walls were made of a single solid layer of brick or stone. During the 1920s it became increasingly common to build houses with an inner and an outer leaf with an air gap in between. This is known as a cavity wall, as opposed to a solid wall with no air gap. 
If you have a cavity wall, then you should check first if you can have cavity wall insulation – or if you have it already. If possible, this is much cheaper than solid wall insulation. 
Some houses are not built of standard brick, stone or block. For example, they may have a steel frame, or could be made from concrete panels. Solid wall insulation may be the best option for these houses.

If you are in any doubt about how you can insulate your walls, you should arrange for an installer to come and visit. They will organise an assessment of your building to determine the best approach for you. 

Internal or external? 

Insulating your walls on the inside is a very different process to insulating them on the outside. There are a number of things to think about when deciding which is best for you. 

There are pros and cons to both approaches:

External wall insulation 


  • Avoids disruption inside the home.
  • Doesn’t reduce the size of rooms.
  • Very effective insulation approach.


  • Likely to need scaffolding.
  • Changes the appearance – may not be allowed.
  • Likely to be more expensive.
  • Need to move or modify outside pipework, guttering, window sills etc.

Internal wall insulation


  • Doesn’t change appearance of house.
  • Can be fitted one room at a time.
  • Can be cheaper than external.


  • Will make some rooms slightly smaller.
  • Need to redecorate afterwards.
  • Need to move or modify skirting boards, radiators, sockets, coving etc.
  • Needs particular care to avoid condensation issues.

Things to watch out for 

  • Adding wall insulation to an older property is a major piece of work, and it needs to be done properly to avoid causing problems in the future.
  • When you insulate the walls of an old house, you change the way that moisture moves through the house. If you insulate in the wrong way, or you insulate a house that already has a damp problem, you could be creating problems for the future.
  • Insulating old houses is a specialist job.
  • Always use an approved installer to specify your insulation solution, and to fit the insulation system. If possible, check that the installer has a good track record in insulating properties like yours.

More information

Visit the Isle of Man's green living grant page for more information.