How to INSULATE a Single Brick Wall?

How should you insulate a single brick wall? Did you know that in the case of an uninsulated facade, twenty percent of the heated heat can be lost through the walls?

That is, of course, a shame!

To prevent this, it is wise to insulate the facade afterward. It is more pleasant in a house with well-insulated external walls. The indoor climate is also healthier. The payback time of facade insulation is relatively short.

In short, applying facade insulation is something everyone should do!

This post explain the isolation (or actually post-isolation) of an apartment from 1916.


What options are there for facade insulation?

There are various options for post-insulating the facade.

Post-insulating between the walls (or cavity wall insulation)

Homes built after 1920 have a cavity wall. The facade of these houses consists of two walls with an open space between 7cm to 9cm (the so-called cavity). Until 1975, the cavity was not filled with insulating material. With an uninsulated cavity, the heat can still easily leave the house. An uninsulated cavity can be reasonably and inexpensively re-insulated. This is a job that you must have carried out by a specialized insulation company. The insulation company can spray insulation material between the walls through small, drilled holes in the outer walls, and thus insulate the cavity wall.


Insulating single-brick wall on the outside of the facade

Homes built before 1920 have no interior and exterior walls. The houses were then built with a single row of bricks for the outer walls. You can insulate a single brick wall on the outside or on the inside.

If you now have a single-brick wall (so no cavity wall), the best way of post-insulation is to apply exterior wall insulation. In the case of external facade insulation, place a completely new facade against the existing facade. This form of post-insulation is drastic (and therefore expensive) and must be carried out by a specialized company. In the Netherlands, you do not see many homes that are equipped with external facade insulation since the appearance of the house changes, and usually, no permit is issued for this.

Insulating single-brick wall on the inside of the facade

In most cases, you will have to insulate the facade of a house with a single-brick outer wall on the inside of the facade.

In this case, there are several ways to apply the insulation material to the inside of the facade. You can place a mitt and fill the space between the outer wall and the mitt with insulation material. Furthermore, there are also insulating materials available that you can glue directly to the inside of the facade on the wall.

The after-insulation of an outer wall of a house from before 1920 requires the necessary attention. Before 1920, there were no internal and external walls. The houses were then built with a single row of bricks for the outer walls. The disadvantage of this was that the houses were not sufficiently protected against moisture, which was not conducive to the construction of the house.

From 1920, the first houses with a cavity wall were built, because this helped prevent the moisture problems. Any house built before 1920, the chance that there is a cavity wall is very small.

Recognize whether the outer wall has a cavity

In addition to the year of construction of your homes, you can deduce from the thickness of the wall, whether the wall has a cavity or not. Go to a doorway and measure the thickness of the walls. With a thickness of 25cm or more, you definitely have a cavity. If you measure less than 25cm, you have either none or a very thin cavity. Below a picture of a single brick wall of an apartment from 1916 that I am going to isolate. The thickness of the wall is 20cm, and as you can see, it clearly has no cavity.

How to insulate a single brick wall?

On the internet, you can read many different ways of how to approach insulating a single brick wall. Since this is a job apartment, you can now immediately get a good foundation (see also “ Renovation starts with a good foundation ”). To properly insulate the outside walls of this apartment, I go through the following steps:

  • Obtain information from various insulation companies. The following companies provide a lot of information:

          De Isolatieshop

          Budget isolate

          De Isolatiehal

  • Search Internet for the pros and cons of the various post-isolation methods;
  • Making an insulation plan of how you want to insulate the different outer walls;
  • Dividing the (isolation) activities into work packages;
  • Approaching various insulation companies and requesting quotes. On the basis of the work packages, you can easily request and compare them differently. You can then decide for yourself whether it is worthwhile to carry out the post-isolation or have it carried out yourself;
  • Summarizing the costs in an overview based on the above information.


Materials for post-insulation

There are many different materials available on the market that you can use for post-insulating the facade. Below are the most common insulating materials that can be used for post-insulating the facade.

Glass wool

Glass wool is usually supplied on rolls (the so-called flange blanket) or as sheets. Glass wool is often used for insulating roofs and behind secondary walls. Glass wool has a good insulation value and is relatively inexpensive. When placing glass wool insulation, make sure you wear a mouth mask/safety goggles and gloves to prevent irritation.

Glass wool properties:

  • Pros: Inexpensive / Light in weight
  • Disadvantages:  Slight irritation when installing/losing insulation value when damp
  • Insulation value: Reasonable / L value of 0.040 [W / (m * K)]

It is best to buy insulation materials such as glass wool from Bouwbestel or the Hornbach.

Rock wool

Stone wool is especially known for its multifunctionality. In addition to thermal insulation, rock wool also contributes to better sound insulation and fire resistance. You can get this in the form of sheets, nail flange blankets, and delta plates that are particularly useful for insulating between joists. The best-known manufacturers of stone wool insulation are Rockwool and Isover.

Stone wool properties:

  • Advantages: Maintaining insulation value and regulating moisture
  • Disadvantages: Price slightly higher than glass wool
  • Insulation value: Good / L value of 0.034 [W / (m * K)]



PIR is short for polyisocyanurate. It is a plastic that is specially intended for the insulation and is mainly known as yellow-white plates. The advantage of PIR insulation boards is that they have a high insulation value. Due to the good thermal properties of the material, it can also be used in small thicknesses. PIR insulation boards are mainly used for insulating roofs, floors, and facades.

Properties PIR:

  • Advantages: The material does not absorb moisture / good fire-retardant properties / high insulation value
  • Disadvantages: Relatively expensive
  • Insulation value: Very good / L value of 0.023-0.026 [W / (m * K)]

Stone wool or PIR insulation boards are also available at competitive prices at Bouwbestel or the Hornbach.


Multipor is a stony material that is supplied in plates. Multipor’s insulation value is comparable to that of glass wool. Multior has the advantage that it is non-flammable, shape and pressure-resistant, vapor permeable, and fiber-free.

Multipor features:

  • Advantages: Non-flammable/easy to process / Can be glued directly to the inside of the facade
  • Disadvantages: Fairly easy to damage
  • Insulation value: Moderate / L value of 0.045 [W / (m * K)]


Cellulose flakes are a woolly insulation material made from old newspaper. These cellulose flakes are blown into the hollow space under slight pressure. This creates a homogeneous layer that is evenly distributed over the entire room. Blowing in cellulose flakes is used as sound insulation but also as heat insulation.

Cellulose properties:


  • Advantages: Quick to apply / Relatively cheap / Prevents pests
  • Disadvantages: Blowing must be done by a professional party
  • Insulation value: Reasonable / L value from 0.036 – 0.039 [W / (m * K)]

How to save costs for post-insulation?

If you decide to carry out certain post-insulation activities yourself, it is wise to see whether you can buy B-choice insulation material. B-choice or 2nd choice insulation material is created at the start of the production line of the insulation material. The start-up of the production line takes a while, and here the production parameters are fine-tuned. As a result, there are often small quality differences in the first batch of insulation material, but the insulation values are good. Common quality differences of B-choice insulation material are:

  •         Minor damage to the corners;
  •         Foil layer not completely tight on the (PIR) plates;
  •         Discoloration of the edges of insulation board materials
  •         Small differences in thickness.

Please note that B-choice insulation material is often only available in limited types. Furthermore, there is usually no warranty on B-choice insulation materials. However, it can make a significant difference in price while still providing you with a well-insulated home.


Make a post-isolation plan.

Each renovation is unique, and you need to consider per situation how you can perform the post-insulation most efficiently. For this specific DIY apartment, I have come to the following post-insulation plan:

Which measures work best in your home depends on the specific properties of your home. You can further develop this insulation plan in consultation with an expert. It is therefore recommended to calculate the Energy Index you will receive after the renovation. By using the after-insulation of your home, you can make a big step in the energy efficiency of your home.

If you do this properly, it is possible to obtain your home an Energy index with an A label!

Let’s quickly go through the steps for insulating a single brick wall!

Post-insulation of the facade with Multipor

In Germany, many homes are insulated using Multipor na. In the Netherlands, however, Multior is still a relatively unknown material for post-isolation. The only companies I could find that could supply Multipor plates and Multior mortar are Eco-Logisch and . I approached the Hornbach and Bouwbestel to check whether they could also supply Multipor plates and Multipor adhesive mortar, but unfortunately, that was not possible.

As stated earlier, the disadvantage of Multipor is that it is relatively expensive and has less good insulation properties such as PIR or Glass wool and Steel wool.

Preparation for placing Multipor

Gluing the Multipor plates to the wall is very easy. However, please note! Before you can actually start gluing the Multipor plates to the wall, you have to do a lot of preparatory work. The following are the steps for the after-insulation of the outer wall using a Multipor.

Step 1 – Bare the wall.

You must glue multipor plates directly to the inside of the outside wall. For this, you must, of course, first, bare the inside of the outside walls. This means removing the radiators, old scraps, and retention walls. According to the supplier (Xella), the Multipor plates cannot be applied directly to a plastered wall. In this case, you also have to remove the gypsum plaster before you can apply for the Multipor plates.

Removing the old stucco/stucco from the entire job is by far the most tedious and time-consuming work.

Step 2 – Leveling the wall.

With the Multipor adhesive mortar, you can remove irregularities of about 5 mm per running meter. However, if there are larger irregularities in the outer wall, you must first level this. For this, I approached Xella to find out what kind of plaster work you should use for this.

According to Xella, level the wall with a lime or lime cement plaster. The Keim or Strikolith companies supply such products. For leveling, I myself used Strikocem plaster MEP + -it 25 kg lime cement. Leveling is fairly easy and does not have to be super accurate.

Step 3 – Ordering Multipor insulation materials

The preparations are ready, and you can finally start after-insulating the outer walls! However, first, order the correct materials and tools. I have the Multipor plates and Multipor adhesive mortar at Eco-Logisch. Ordered the following for this post-insulation job:

  • Multipor plates 50mm thick
  • Glue mortar
  • Reinforcement mesh

è Please note that I did not buy this from Eco-Logisch, but simply from the hardware store. This saved ~ 50% in costs.

  • Hemp strip
  • Glue spreader

When placing the Multipor plates, you have little cutting loss, so you can order the quantity fairly accurately. Below a picture of the Multipor plates and the Multipor adhesive mortar after delivery:

Step 4 – Placing Multipor plates

After the wall you want to insulate has been leveled, you can start placing the Multipor plates. Finally! Under the Multipor plates, I placed a foam rubber insulating tape to prevent damage to the Multipor plates. Not quiet sure if this is really necessary, but it worked really well.

You will notice that once you have the first strip, applying the Multipor plates is easy. In short, now it is a matter of making meters! Within a few hours, this is the end result:

Step 5 – Finishing the edges.

New plastic frames were first installed for this specific DIY apartment. After applying for the Multipor plates, you can also immediately finish the frame neatly.

It seems to be the easiest to finish the frames with plaster plates so that everything can be plastered tightly at once. I first cut the plaster boards to size. Then coat the ends of the Multipor plates with Multipor adhesive mortar.

After this, you can fix the plasterboard with screws in the plastic frame of the plastic frames and glue the rest of the plasterboard with the Multipor plates. This way, you can neatly finish the frame on all sides, and the plasterer can plaster and finish everything smoothly in one go.

Step 6 – Placing reinforcement mesh and plaster

As indicated, I had just bought reinforcement mesh from the hardware store instead of the special Multipor reinforcement mesh. The reinforcement mesh is best applied during plastering. Since I did not do the plastering myself, the plasterer applied the reinforcement mesh.

Insulate single-brick wall with PIR plates

As indicated, you must be careful about moisture problems when insulating an external wall. PIR panels seem to be the best solution for the bay window of the living room. After the wooden scraps have been removed, it appears that there are beautiful wooden Rachels on the wall. Wooden racks are approximately 25mm thick and can serve as a nice base for screwing on the PIR plates. This creates an air gap of 25mm between the inside of the outside wall and PIR plates.

To carry out this job as cheaply as possible (but with good insulation properties), I bought B-choice PIR plates. These PIR plates have small imperfections on the sides, and the foil is not completely stuck over the PIR plates. See below the B-choice PIR plates after delivery:

Step 1 – Bare the wall.

After all scraps and other old debris have been removed from the walls.

Visually, it may not look very sleek now, but the wood shavings are still of excellent quality after nearly 100 years. In short, an excellent basis for the PIR plates.

Step 2 – Placing PIR plates

The PIR plates are easy to cut with a hand saw. The processing is also fairly clean, and you do not get itchy from the sawdust of the PIR plates. Make sure that you use a good large ring/saucer under the screw when screwing the PIR plates. Otherwise, you will not get the PIR plates properly, and the screw will simply go through the PIR plate!

Step 3 – Finishing the PIR plates.

I was told that you could also plaster PIR plates. Unfortunately, this is not true! The plasterer was very clear about this. So before the PIR plates could be plastered, it had to be finished with plaster plates. In short, place the stucco plates on top of the PIR plates. You can screw the plasterboards nicely at the wooden Rachels.

Step 4 – Plaster

As with post-isolation, the plastering was not done by me. Make sure that everything is well finished with plaster plates, and the plasterer will plaster everything completely smooth.

Insulate single-brick wall with cellulose

Post-insulating a facade with cellulose is not something that happens a lot. Post-insulating the bay window with Cellulose was an efficient solution for this specific DIY apartment. After the old stucco plates were removed from the scrap, you could view the hollow wall of the bay window by removing a scrap. The hollow wall of the bay window was nicely dry and allowed to apply a 120mm thick cellulose layer.

Step 1 – Ordering cellulose material

I have engaged a professional party to blow in the cellulose material. He also immediately supplied the Cellulose insulation material. In this case, Easycell cellulose was used. Below a picture of how the Easycell insulation material is delivered:

Step 2 – Drill holes in scraps

To blow the cellulose flakes into the facade, you have to drill holes in the scraps at regular intervals. There shoul be no gaps or openings for the cellulose flakes to escape during blowing.

Step 3 – Blowing in cellulose flakes.

The next step is a matter of blowing in the cellulose flakes. After the cellulose flakes are blown in, a stopper of cork goes into the hole. Then you can continue blowing the cellulose flakes into the next hole.

Step 4 – Finishing and plastering

After the entire facade of the bay window has been blown in with cellulose flakes, you can finish everything with plaster boards. This is fairly fast and does not have to be super tight since everything will be plastered after this.

End result

The post-isolation of the handy apartment has reduced the Energy index from “label D” to “label A.” This includes that double glazing (HR ++ glass) is also placed in the apartment everywhere.

Nevertheless, after insulating a 1920s apartment, you can achieve major improvements in the sustainability of your home. In short, a good investment for the environment, but also for your own wallet!


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