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Energy efficiency: Wall and loft insulation

All homes lose heat, but ensuring homes have the appropriate level of insulation will reduce this heat loss, and save money.

A typical home will lose a lot of heat through different parts of the house. The two largest areas are through the walls (which accounts for 35% of all heat lost) and the roof (the next 26%), which together account for over half the total amount. 

Tackling these areas can therefore have a significant effect on how warm a house is, and how much it costs to heat.

See if you are entitled to any grants or loans towards insulating your home.


Solid or cavity wall insulation

The first step towards making a saving is to find out which sort of walls your home has.

There are 2 main types of external wall: solid wall; and cavity. Most homes built after the early 1930s have cavity walls. That means your walls have an inner and outer layer separated by a small air gap.

You can usually tell which sort of wall you have by measuring their thickness at any window or door. Cavity walls are at least 300mm (12") thick, whereas solid walls are normally only 225mm (9") thick. The brick patterns are also different, compare the cavity wall (top) with the solid wall (bottom) in the picture.


 Cavity wall insulation

This is a straightforward job that can be done in a day. It should always be done by a professional installer, who will inject insulating material from outside into the cavity by drilling small holes in the wall.

It causes little disruption and is surprisingly inexpensive considering the amount it will save you in the long run. It can reduce heat loss through walls by up to 60%.


Solid wall insulation

Solid wall insulation can be either external or internal.  The Energy Saving Trust's guide to external wall insulation

Talk to Building Control before doing any solid wall insulation to make sure it meets with the current regulations.

External solid wall insulation

This is more complicated and costly than cavity wall insulation, and a professional installer should do the work.

There are a number of ways this can be done:

  • it might involve rendering insulating material directly onto the wall
  • applying rigid insulation boards reinforced with a decorative render finish
  • metal carrier system rendered over

In all cases, the work may represent a significant change to the visual appearance of the building, and it is worth discussing this further with the planning department to see whether planning restrictions apply to your house because of its age, appearance or location.

It is important that this work is undertaken to a high standard, because poorly installed or poorly detailed solid wall insulation will not be effective, and may cause further issues over time.

Internal solid wall insulation

Internal solid wall insulation can be relatively cheap, especially if you do it when your walls need repairing or redecorating. It is, however, still a major piece of work; you will have to take off and refit all skirting boards, doors and window surrounds on the outside wall.



Various types of insulating material can be used: foam, mineral wool (rock or glass), or polystyrene beads. The cost depends on the type of material and the size of your house.

Professional installers will provide a 25-year guarantee from the:

This guarantees that any defect in materials or workmanship, in connection with the installation by a member installer, will be put right without charge to you.


Loft insulation

Your home may already have some loft insulation, but if the material is thin, it won't be saving you as much as it could. Fitting proper loft insulation is the easiest and most cost-effective way of saving energy.

The thicker the material, the greater the saving. If you have older, thinner loft insulation, think about replacing it with new material at least 270mm (11") thick. This can save around 20% of your heating costs.

Types of loft insulation

You can get loft insulation from any DIY store or builders' merchant. Make sure that you wear the correct safety clothing, or ask an installer to do the work for you.

There are 3 main types of loft insulating material:

  • blown mineral wool or blown cellulose fibre

  • mineral wool quilt

  • loose fill

Only the latter 2 types are suitable if you are going to do the work yourself.

Heat loss

Heat loss is greater from certain areas such as around joists, so remember to lay the top 100mm (4") of insulation over the top of them.

You will need a boarded passage to enable you to reach tanks in the loft. Don't forget to insulate and draught proof the hatch too.


Good loft ventilation is essential to minimise the risk of condensation and subsequent wood-rot. Most homes already have adequate ventilation, but check yours anyway, just to be on the safe side.

  • Modified: Jun 17, 2016 12:52:25 PM