Solid Wall Insulation and How it Works

Solid Wall Insulation and How it Works

Wall insulation is a need in countries with colder climates. Depending on the type of walls your house has, there are two types of insulation methods to keep your home cosy during the chilly months.

There is cavity insulation, which is installed in recently built houses having hollow walls. It costs less compared to solid wall insulation.

Old houses constructed in the early 1990s have solid walls, i.e. the outer walls do not have gaps in them. They are packed and not hollow from inside. Solid walls can be kept warm from the interior or exterior of the house. This certainly costs more than cavity insulation but saves a lot later on the heating bills. In this article, let us look at solid wall insulation and its working mechanism.

Solid wall insulation is perfect for brick or stone-made houses and can be done either from the inside of the house or outside.

 It works by adding a thermal or heating material’s layer on the inside wall. This would decrease the rooms’ size a little; however, it makes the house cosy and more comfortable. Internal solid wall insulation is beneficial to preserve the outer appearance of buildings or heritage mansions, having a rich history. The insulation material can also be added to the exterior wall as well. This is called exterior solid wall insulation.

Determining the type of walls by looking at the brick pattern

In brick made homes, if the bricks are arranged in an alternate long-short-long way, then the walls are solid. If the long edge is visible on the corners, then they are cavity walls. If bricks are hidden, then the wall type can also be determined by gauging the thickness of the wall near the entrance or the windows.

Solid walls are 22 cm thick, whereas cavity walls are between 27 to 30 cm thick. A solid stone wall could be 50 cm thick, but it can be found at very old buildings and mansions, not recent construction. Similarly, if a house was constructed before the1920’s, it wouldn’t have cavity walls as stone walls were the order of the day back then.

Internal Solid Wall Insulation

Solid Wall Insulation and How it Works

Insulating a wall from within can be done in four ways.

Rigid insulation boards

Insulation boards are fitted on the inside walls. You can choose from numerous kinds of materials and thicknesses. The kind of materials chosen has an impact on the energy costs too. Better quality gives better insulation and prevents heat from escaping out. Some materials have already attached plasterboards that make the process of installing the boards easier and less time-consuming.


Some houses have a lot of cupboards, bookshelves, wall hangings attached to the walls. Then drylining is the best option for such homes. In this, battens are carefully placed on the walls and insulation material is then installed amidst them. It is then coerced with plasterboards.

Thermal lining

The thermal lining method is quite simple but may not be effective for many houses. The lining comes in bundles or rolls and can be stuck on the walls using strong glue. The linings are about 10mm thick and can provide fine insulation at a low cost. It is ideal for houses with very small rooms.

Insulated plaster

Houses having uneven or rugged walls can go for insulated plaster to get airtight walls. It is a mixture of plaster and thermal material like cork or mineral wool fibre. It is applied on the walls or even sprayed to close the exposed holes in the walls and prevent the heat from escaping out.

How to deal with moisture

It is important to know that most solid walls are vapour-open and allow moisture to pass through them as they were built that way. If we use a material like foil-faced insulation foams, then moisture could be retained inside the walls leading to the development of mould, fungus and dampness. Hence, if the wall is ‘vapour open, then we should use ‘vapour-open insulation substances’ such as wood fibre, mineral boards, cork etc. These materials, once fitted, should be covered with lime-based plaster and airy paints that do not trap moisture.


Opting for internal wall insulation would cost around £5,500 and £8,500. This could vary based on the number of rooms, their size and the type of material being used. Internal wall insulation is less expensive than external insulation. For instance, a three-room semi-detached house could save £260 annually on heating costs by going for internal wall insulation, whereas a detached house could save around £430 every year.


Internal wall insulation may leave our house in need of a renovation afterwards; the process causes some disruption.

The rooms where the heating boards are being installed cannot be used, and other household items and furniture would have to be shifted to other rooms. Wall fittings such as skirting boards, radiators, window sills, plug joints etc., will have to be removed from the walls while the work is going on.

 They would also remove pipes and electric wiring, which would require to be re-laid. Also, a lot of dust and noise is produced. Regular water and electricity supply is a must. After the work is done, the walls and nearby surfaces would have to be refurbished, and all the furniture has to be rearranged.

External Solid Wall Insulation- How does it work

Solid Wall Insulation and How it Workss

This comprises a layer of insulating material added to the exterior walls and covering it with protective coating or cladding. There are many materials and thicknesses to choose from. These may add a fine finish to your house as it is installed externally. If done properly, it could completely change the looks of the house.

Why to got for external solid wall insulation?

This insulation method is ideal for people who want to save space inside their homes or do not want to get disturbed. In exterior insulation, all the extra work is saved. This system is installed from the outside, so you do not have to worry about shifting furniture or moving things. It does not take much time as well and is a pretty straightforward process.

Some things to keep in mind

The size of the rooms doesn’t change with external solid wall insulation, but the outer appearance of the building might be alternated considerably. This would require getting planning permission from the designated authorities. There are numerous contractors with whom you can decide the materials to be used and the paint to be applied so that it goes with your style.

Nowadays, you don’t need planning permission as solid wall insulation is undertaken for the improvement of insulating systems. However, f your house is near the National Park or a conservation area, or within a UNESCO World heritage site parameter, you could double-check it with the local authorities before getting the work started.


External insulation costs about £13,000. However, this also depends on the size of the house and the number of outside walls that have to be insulated. It is costlier compared to internal wall insulation as material and labour cost is higher and requires a skilled labour force.

For instance, a 3-roomed semi-detached house using gas heating could save £300 every year and a detached house around £700 annually by opting for external insulation.

Disruption caused

External solid wall insulation might not affect the interior, but it takes up space outside while the work is being completed.

The garden might not be accessible for some time, while boundary walls or any other structures might suffer. There would be a need to get scaffolding and make room for skip and space for storing materials.

House fittings such as rainwater pipes, telephone cables or satellite dishes would have to be temporarily removed.

The work would require a lot of tools to work on stone walls, and hence a lot of noise and dust particles would be released.


External insulation has some benefits too. It does not cause any disruption inside the house and does not decrease the floor area. The process makes your outer walls look new and gives a new appearance to the house too. It would also improve weatherproofing and make your walls a lot of sound resistant, giving you a peaceful and cosy home.  This process makes the outer walls airtight by filling in any cracks in the brickwork. Thus, it protects the brickwork and also decreases moisture on inside walls, preventing dampness and mould.

How to save cost on solid wall insulation?

It is advised to get the external heating system installed when you are getting your house renovated to save on additional costs. Since it requires exterior walls, they should be in good condition. The walls should not be damp or weak.

If you have less money in your hands, you could choose to install the heating system in one of the rooms or exterior walls and progress slowly with the work.

External insulation would be cheaper if you get it done while tackling repair work in the garden or the roof. In this way, you could give out the contract for all the work to one firm, which could save you some money. For example, if you are getting a new roof, or solar panels, or a new garden layout, then there would be scaffolding there, so you can go for external insulation also.