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Solid wall

Insulating your solid walls could cut your heating costs considerably, and make your home more comfortable.

If your home was built before the 1920s, its external walls are probably solid walls rather than cavity walls.

  • Solid walls have no gap, so they can’t be filled with cavity wall insulation.
  • Cavity walls are made of two layers with a small gap or ‘cavity’ between them.

Solid walls can be insulated though – either from the inside or the outside. This will cost more than insulating a standard cavity wall, but the savings on your heating bills will be bigger too.

solid wall insulation

Work out your wall type

If you have solid walls, then they’re almost certainly not insulated - but the first thing you need to find out is what sort of walls you have.

If you can see the brickwork on the outside of the house, look at the pattern of the bricks as this can show how the wall has been built.

  • If your home has solid walls, the bricks will have an alternating pattern, with some bricks laid across the wall so you can see the smaller ends from the outside.

solid wall - bricks

  • If your home has cavity walls, the bricks will usually have an even pattern with all the bricks laid lengthways.

old red brick wall id980299714

If the brickwork has been covered, you can also tell by measuring the width of the wall. Examine a window or door on one of your external walls.

  • If a brick wall is more than 260mm thick then it is probably a cavity wall.
  • A narrower wall is probably a solid wall. Stone walls may be thicker still but are usually solid.

If you live in a house that has a non-traditional construction such as a concrete, steel or timber-framed building, you will need a specialist installer with experience in insulating your building type to advise you on your options.

man with a folding ruler

Costs, savings and financial support

Typical installation costs* of solid wall insulation can vary as follows:

  • External wall insulation: around £13,000
  • Internal wall insulation: around £7,400

*Based on a typical semi-detached house in Great Britain

You might be able to reduce these costs by carrying out the work at the same time as other home improvements or by not tackling the whole house at once.

Savings in England, Scotland & Wales


Savings in Northern Ireland 


Lowering the costs of installing solid wall insulation

The costs we suggest for installing solid wall insulation are for paying a company to come in, insulate your whole house in one go, fully redecorate and replace everything just as it was. Some people want exactly this, but it does cost a lot of money. If you're looking to spend less, it is advisable to insulate a wall when you are having other building or decorating work done.

Internal insulation can be fitted when you’re planning to redecorate anyway, or to fit a new kitchen or bathroom. You can also spread the cost by tackling one room at a time.

External insulation will also cost less if you fit it when you're having other work done to the outside. If you're having a new roof, or painting the windows, or even having solar PV panels fitted, then you will probably have scaffolding up already, which can save a bit on the costs. If your walls need re-pointing or other repair work, it’s worth getting a quote for a complete refurbishment including insulation – it will probably work out cheaper than doing the two things separately.

Sometimes there is financial support available to help with the cost of solid wall insulation. Contact your local authority to see if there is any help in your area, or read about financial support in Scotland.

Internal vs external insulation

Internal insulation

Internal wall insulation is done by fitting rigid insulation boards to the wall, or by building a stud wall filled in with insulation material such as mineral wool fibre.

  • Generally cheaper to install than external wall insulation.
  • It will slightly reduce the floor area of any rooms in which it is applied (the thickness of the insulation is around 100mm).
  • It it quite disruptive, but can be done room by room.
  • It requires skirting boards, door frames and external fittings to be removed and reattached.
  • It can make it hard to fix heavy items to inside walls – although special fixings are available.
  • You'll need to fix any problems with penetrating or rising damp beforehand.

Find out more about choosing internal wall insulation.

insulation board fitted between timber frame

External insulation

External wall insulation involves fixing a layer of insulation material to the wall, then covering it with a special type of render (plasterwork) or cladding. The finish can be smooth, textured, painted, tiled, panelled, pebble-dashed, or finished with brick slips.

  • It can be applied without disruption to the household does not reduce the floor area of your home
  • It will renew the appearance of outer walls.
  • It will improve weatherproofing and sound resistance.
  • It fills cracks and gaps in the brickwork, which will reduce draughts.
  • Increases the lifespan of your walls by protecting the brickwork.
  • Reduces condensation on internal walls and can help prevent damp (but will not solve rising or penetration damp).
  • It is best installed at the same time as external refurbishment work to reduce the cost.
  • It may need planning permission - check with your local council.
  • It requires good access to the outer walls.
  • It is not recommended if the outer walls are structurally unsound and cannot be repaired.

mineral wood insulation on exterior of solid wall building

Find out more about choosing external wall insulation.

Moisture movement and ventilation

In traditionally built properties with solid walls, water vapour can usually move quite freely through the building. This is partly because of the high levels of ventilation and draughts, but also because water vapour can travel through the bricks and stones that the walls are made of. When you insulate an older building, you will change the way that water vapour behaves in several ways:

  • Adding wall insulation will usually cut down on draughts through the walls and round the windows
  • The insulation may create a barrier to vapour movement, depending on what materials are used
  • Adding insulation to the inside of a wall will make the wall colder. This means that any water vapour entering the wall from inside will get a lot colder, and may condense inside the wall

Whenever you fit solid wall insulation to a building you need to take account of water vapour to make sure that you don’t create new damp problems in the future. This may involve using “breathable” insulation materials that will allow the vapour to carry on permeating the walls, or it could involve creating a continuous vapour barrier to make sure no vapour can get into the walls from the inside. You will need an experienced specialist installer to develop a moisture control strategy that is specific to your building.

You should check with your installer that the installation is covered by an appropriate 25 year guarantee. They may be members of the SWIGA guarantee scheme, or they may offer an independent insurance-backed guarantee. You can find a list of Ofgem approved guarantee schemes here.

More information

Cavity Wall Insulation

Does your home have cavity walls that need to be insulated? Visit our page for more information, costs & savings and installers.

Cavity Wall

Home Improvements Guide

Are you planning other energy efficiently upgrades in your home? See our Home Improvements guide for more information.

Home Improvements

Based in Scotland?

You can visit or chat with homeowners who have already installed insulation in their hard-to-treat home using our Green Homes Network (GHN) tool. For a free home visit, call Home Energy Scotland on 0808 808 2282 (Monday-Friday, 8am-8pm and Saturday, 9am-5pm).

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