It is almost always a good idea to insulate the outer walls of the house, if the house has not already been insulated. Here you can get some advice on how best to approach post-insulating the outer walls.
Why insulate the outer walls of the house?
A large part of a house’s so-called climate screen is the walls. The area of the walls is usually significant compared to the area of the floor and ceiling, so it is therefore very important that the walls are sufficiently insulated.
In a poorly insulated house, a large part of the heat disappears through the outer walls. Therefore, it is often a very good idea to have the outer walls post-insulated.
Because the heat loss through the outer walls, especially in older houses, is large, it is one of the areas of effort within energy renovation where noticeable savings can be made.
When do the external walls need insulation?
As a rule of thumb, the house’s outer walls need to be insulated if:
- The outer walls have not been re-insulated.
- The outer walls are leaky and in poor condition.
Types of external walls and their typical insulation
The houses we meet typically have three different types of external walls.
- An uninsulated cavity wall..
- A heavy solid external wall of aerated concrete or lightweight clinker concrete.
- A light exterior wall covered with boards, fiber cement boards or a shell wall.
When do the external walls need insulation?
If the outer walls of the house are not insulated, it will always be a good idea to have the walls post-insulated.
It is the first 10-20cm of insulation that really makes a difference. The more insulation there is already, the less benefit additional insulation has. So if there is less than 10 cm of insulation in the outer walls, it would be an advantage to insulate. It will also be profitable and comfort will be improved significantly.
Is it profitable?
It will always be profitable to fill up a cavity wall with insulation, whereas it is rarely profitable to carry out an external post-insulation of a cavity wall that has been filled. If there are drawings of the house, you can check whether the house’s outer walls were originally insulated.
It is often a good idea to have a professional assess the condition of the external walls, as the drawing material and reality do not always match. It is therefore a good idea to have the house’s climate screen examined by a professional, for example using a thermography camera, which can reveal where the heat loss is greatest. Or you can check by simply drilling a small hole in the outer wall, where you can determine whether there is insulation in the outer walls.’
Are the exterior walls tight and in good condition?
A thermographic image shows the surface temperature of the building parts of the facade.
There is a big difference between brick exterior walls and wooden exterior walls.
The condition of brick exterior walls is assessed based on the appearance of the joints. Whether there are cracks or whether they are crumbling. If the bricks are cracked and the fire shell has disappeared, the walls are not in such good condition. It is not common to feel drafts from a brick exterior wall. Then it must be in really bad condition or uninsulated.
If you have wooden outer walls, you can check whether there are drafts from the outer wall, whether the outer side is worn down, or whether there are shields inside. Then the reason may be that the walls are in poor condition.
If you have teamed up with a building expert to assess the condition of the walls, he or she can take a photo of the outer wall with a thermography camera. The photo shows whether there are places where the wall is leaking and the heat escapes.
If the outer wall is old, leaky and poorly insulated, you should re-insulate it. There are generally three different ways to insulate an external wall:
- External walls with cavities between the front wall and the back wall can be insulated with cavity walls.
- External walls can be insulated from the outside.
- Outer walls can be insulated from the inside.
Cavity wall insulation
If the house has a cavity wall that is not already insulated, cavity wall insulation will be a relatively cheap and easy method, which also provides good heat savings. If the brick exterior wall has many cracks in the joints and/or fallen out joints, moisture damage can occur. Cracks and fallen out joints must therefore be repaired before cavity wall insulation is blown in.
Insulation of the outer walls from the outside
You can also save heat if you insulate the outer wall from the outside. This is a good solution in houses that do not have a cavity wall, i.e. houses with a wooden frame or solid outer walls. It is significantly more expensive because a new facade has to be built outside the insulation. In return, you get the facade renovated and sealed at the same time, and you get all thermal bridges removed, as the house gets a so-called ‘overcoat’.
It is also a really good idea in houses with solid external walls, where the insulation is typically fixed to the existing wall and plastered afterwards. When a house with solid outer walls is insulated from the outside, you also gain the additional benefit that any previous interior insulation can be removed, and the solid walls can therefore absorb and release heat. This means something both for comfort and the heating bill.
It is becoming popular to also post-insulate older houses with hollow walls from the outside to eliminate the thermal bridges that are in this type of house around windows and doors and in separating floors for the cellar. The cold bridge consists of the brickwork in these areas being solid, i.e. that there is no insulation.
Insulation from the inside
Internal insulation of the outer wall is generally not recommended. If the vapor barrier is not made completely tight, and remains tight, problems with mold can quickly arise. You can easily damage the vapor barrier if you hammer nails into the wall or similar. But there may be cases where it is the only option. If your house is registered as worthy of conservation, the municipality can set special requirements for the design of the facade, which is why cavities or internal insulation may be the only solution for the climate screen.
Internal retrofitting can also be an option if you only want to insulate the outer wall in a single room.
Is professional advice necessary when you need to insulate your house?
It can be difficult to decide which solution is the best in your house. It therefore often pays to get help from an energy advisor, energy consultant or building expert if you are in doubt about what you should do.
Professional advice will at best save you a lot of money, because the adviser can partly help you find out what to do with the external walls, and partly can help you clarify whether insulating the external walls is the right thing to do or the only place to start if you want to energy-renovate your house. It could give you an overview of the building’s climate screen as a whole, which you can then use when you need to draw up a realistic and effective maintenance plan for your house.
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