Solid Wall Insulation

More heat is lost through solid walls than through cavity walls – up to 45% of the heat in a solid walled home is lost through the walls. Insulating your solid walls can save you around £345 per year on your heating bills according to Energy Saving Trust studies.

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How it Works

There are two way of insulating solid walls:

  1. Internal Solid Wall Insulation – This applies the insulation to the inside of your home’s walls.
  2. External Wall Insulation – this applies the insulating material to the outside of your external walls.
    It will depend on the situation which is best – internal insulation is cheaper, but takes away living space and is slightly less effective. You may also save money by installing internal insulation at the same time as carrying out other decorating work.

Do I have Solid Walls?

Solid walls are external walls built as one wall without a cavity. This was the common building practice before the 1930’s.

  1. If you home has brick or stone external walls and was built prior to 1920 it probably has a solid wall.
  2. The way the bricks are laid can tell you; if there is a cavity the bricks tend to be all laid lengthways, whereas solid walls have bricks alternately laid length ways then end-on (across the wall rather than along it so that one end is on the internal side of the wall and the other on the external side)
  3. If you are in any doubt your installer will be able to confirm exactly what type of wall you have and recommend the most suitable method of insulation.

If you don’t think you have solid walls, remember that cavity walls can be insulated too. Find out more details about insulating Cavity Walls.

Will it work on my home?

Yes, but here are some considerations:

  • You should have a solid wall or a cavity wall that is not suitable for cavity wall insulation
  • You will need to decide which is best for you; internal or external insulation
  • Try to combine installation with other work such as re-rendering or internal decorating

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Internal wall insulation

There are two types of internal solid wall insulation:

– Insulation board

This involves attaching insulation board covered in plasterboard to your walls. This will typically be around 60mm in depth but can reach 100mm. The boards are attached with either plaster or adhesive and the joints between the boards are also sealed.

– Stud wall

Mineral wool is used to fill a metal or timber studwork frame attached to the wall, which is then covered in plaster. This plaster can be replaced with insulation board. The frame will need to be at least 120mm, as mineral wool is a less effective insulator than insulation board. A stud wall may be ideal if your wall’s surface is uneven.

Both types will be able to support attachments such as cupboard units. For either type you will have to remove all door frames, skirting boards and other fittings before installation and refit them afterwards. Internal insulation will make any wall-based damp problems worse, so you should sort these out before installation.

External wall insulation

External insulation involves attaching a layer of insulation material to the outside of your house and covering this with a layer of cladding or render. This layer can be finished in a number of ways – it can be covered with brick slips or tiles, pebble-dashed or painted. External insulation should only be fitted if the external wall is sound.

Pros and Cons

  • Internal insulation is generally cheaper to install but saves less money on energy bills
  • Internal insulation will cause more disruption to your home
  • Internal insulation will take up around 100mm of living space along all of your outer walls.
  • External insulation alters the appearance of your house
  • External insulation can increase the life of the wall by protecting the brickwork, and it will reduce draughts by filling cracks or gaps. It will also provide extra soundproofing.
  • External insulation will require planning permission if your home is a listed building or you live in a conservation area.

Both should:

  • Reduce condensation on internal walls if fitted correctly
  • Require good access to the wall for insulation
  • Significantly reduce heat loss – by over 40% in many cases
  • Be fitted by a professional installer

Ensure that your installer is a member of a recognised professional body. We will only recommend certified installers.

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Costs and Maintenance

The Energy Saving Trust estimates that the cost of installation in a 3 bedroom semi-detached house will be between £5,500 and £8,500 for internal insulation. It is substantially more for external insulation, at between £9,400 and £13,000. If you are already planning work to your home this cost can be incorporated in the cost of your renovations.

The ECO scheme is a new scheme funded by UK energy suppliers due to launch at the end of January 2013. It offers loans to partially or fully fund any solid wall insulation installation, regardless of your economic circumstances. You can register your interest for the scheme here:

Just like loft and cavity wall insulation, there is no maintenance over and above what you would have to do to walls of your home anyway.


The annual saving for a 3 bedroom semi would be in the region of £445, and more for External insulation, being up to £475. Some estimates are more but this will depend on your home.

For Landlords there are tax allowances of up to £1,500 for insulation projects.

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How can I tell if my new home's previous owners have already insulated the cavity walls?
If a house was built within the last ten years, it probably has cavity wall insulation installed as slabs when the walls were built. You can tell if previous owners have had it installed after the house was built by looking at the outside of the external walls under your windows. If there are small holes of about an inch diameter filled in with something, this indicates that your walls have been filled with insulation. Another way to tell is by looking at the tops of your external walls, which may be open under your roof. If you can look inside the tops of the walls you may be able to see whether there's any insulation in them.
How do I find out how much loft insulation I have?
Simply push a tape measure or ruler down the side of a piece of loft insulation until it hits the plasterboard ceiling and read off the depth.
I have lots of rubbish in my loft. Do I need to clear it out or will the installer do this for me?
Yes, you will need to clear the roof of any rubbish or stored objects before the insulation is installed.
How long would it take me to insulate my loft?
Allow about half a day once you have bought the insulation. Remember - you will need one layer of 100mm between your roof joists if you don't have any insulation, then a second layer of 170mm on top (cross layered) to comply with current building regulations. Measure the area of your loft and look at the packaging label for the area contained in a roll.
I already have some loft insulation - do I need to install more?
If your loft insulation is 100mm or less you would certainly benefit by having it topped up with more insulation to make it up to a 270mm thickness. The Energy Saving Trust estimates that top-up loft insulation can save the average householder as much as £60 per year at current energy prices.
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