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Solid wall insulation - internal

Nearly half of all the heat lost from some solid-walled houses escapes through the walls. Insulating these walls will slow down the rate at which heat is lost and keep the warmth inside the home for longer.

Solid wall insulation may be suitable for a variety of property types such as brick, stone, steel-framed and concrete construction.

Internal solid wall insulation works by adding a thermal layer of material to the existing wall. Solid walls can be insulated internally (from the inside) and externally (from the outside). Both are significant undertakings in terms of cost and disruption but both options can make your home warmer and greatly reduce your heating bills at the same time.

Internal solid wall insulation, rather than external, is particularly appropriate where you need to maintain the external appearance of the building (e.g. in a heritage context).

How do I know if my home has solid walls?

If your home is made of brick, and the bricks have an alternating long-short-long pattern like this, then the walls are likely to be solid. If you can see only the long edge of the bricks, like this, then they are almost certainly cavity walls.

If the brickwork is not visible, measuring the thickness of the wall at any entrance or window will help to determine the construction type. A solid brick wall is usually about 22cm thick, a cavity wall between 27cm and 30cm and a solid stone wall as much as 50cm thick. The age of your home can also be a good indicator; if it was built before the late 1920s it is likely to have solid walls.

Types of internal solid wall insulation

There are various ways to insulate a solid walled building from within, but they broadly fall into three categories:

1) Rigid insulation boards

These come in a variety of materials and thicknesses and deliver the highest energy saving. Some have pre-attached plasterboard which makes the installation process more straightforward.

 2) Dry lining

Battens are fixed to the walls, insulation is fitted between them and then covered with plasterboard. This is a good option if the wall has a lot of heavy fittings such as book cases or kitchen cupboards, or if the original wall is rough and uneven, as in some stone properties.

3) Flexible thermal lining

This comes in rolls like thick wallpaper and is glued to the wall using a special adhesive. Flexible linings may not provide the same level of insulation but you could install the material yourself if you are a competent DIYer. Moreover, as flexible linings tend to be no more than 10mm thick they can be a good option for rooms that have limited space.  

Average cost and savings

Internally insulating your home will probably cost between £5,500 and £8,500, depending on how many rooms are being renovated and the type of material being used. Generally this is less expensive than external solid wall insulation because of the lower cost of materials and labour. A typical 3-bedroom semi-detached house using gas heating could save around £260 per year on heating bills by installing internal wall insulation whereas a detached house heating with oil could save around £450 per year.

Disruption

Internal solid wall insulation is a significant undertaking that inevitably involves a degree of disruption. Your installer should make you aware of any particular issues but things to consider include:

  • A skip may be required
     
  • Rooms where the work is being done may not be usable whilst the work is being carried out and furniture, kitchen units etc may need to be temporarily removed
     
  • Fittings such as radiators, skirting boards, window sills and plug sockets that are on the wall that is being insulated will need to be removed and reattached afterwards
     
  • Pipe work and wiring may need to be re-laid
     
  • The works will produce dust and could be noisy at times
     
  • Contractors will require water and power, and the use of a toilet
     
  • The newly insulated walls and adjacent surfaces will need to be re-decorated when the work has finished.

Internally insulating a wall will reduce the size of your room. However, by making a cold wall warmer you may find you have more usable space.

A cut-away model of internal solid wall insulation.

1 | Surface coating (green)internal solid wall insulation

This is the new plasterwork that covers the insulation layer. Just like a normal internal wall, it can be painted (green in this case) or papered

2 | Insulation (orange)

This is the layer that prevents warmth escaping through the outside walls of the house. In this case, rigid insulation boards have been used.

3 | Internal wall (white)

This is the old internal plaster which is now covered by the new insulation board and plasterwork.

4 | Windows

Ideally, the insulation board is fitted to the inside of the window recess to prevent cold patches developing where condensation forms. But, as is the case here, this is not always possible.

5 | External wall (brickwork)

From the outside, your property will look exactly the same.


Image: Will Anderson 

Frequently asked questions

Aren't all walls, 'solid walls'?

The term 'solid wall' refers to walls constructed as a single solid layer with no cavity section within the wall. This means the wall is literally solid from inside to outside. Solid walls are typically made from brick or stone, and are generally found within houses built before the 1930s.


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How can I insulate solid walls?

Insulation for solid walled properties can be carried out on the inside (internal wall insulation) or the outside (external wall insulation) of the property. To fit internal wall insulation any fixtures and fittings must be removed and refitted afterwards. This includes switches, sockets, skirting boards, kitchen units, etc. To fit external wall insulation you may require scaffolding and fixtures such as drain pipes and satellite dishes may need to be removed and refitted afterwards.

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What is 'thermal mass' and why is it relevant when considering solid wall insulation?

Solid brick or stone walls will absorb heat from both inside and outside of the property during the day, acting as a heat sink. Their relative ability to do this is known as their 'thermal mass'. Some of the heat absorbed by the walls is released back into the house when the temperature drops, typically after dusk. In the winter external wall insulation will allow more of the heat that is produced in the home to be absorbed into the walls and then be released back into the building, rather than passing right through the walls to the air outside. External wall insulation will also reduce the absorbtion of heat from the outside by the walls in summer. This will help stop the home becoming too hot on the warmest days. In the winter internal wall insulation will do a good job of keeping the heat produced by your heating system in your home. However it is not as good at taking advantage of the thermal mass because of the barrier it creates between the heat in your home and the walls.

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