The federal government is spending hundreds of billions of euros to cushion the high energy prices. Still, Arnold Drewer is furious. Because the terms “energy efficiency” and “thermal insulation” hardly ever appear in the relief plans, criticizes the managing director of the Institute for price-optimized energetic building modernization (IPEG). “Inexpensive insulation measures would also be really sustainable in the interests of taxpayers,” explains the energy expert in ntv’s “climate laboratory”. Because they would not work for one or two years, but for 50 to 100 years – depending on how long the house has been standing. At what price? 3000 to 4000 euros for core insulation. “With the current energy prices, the costs will be recouped in four years,” Drewer calculates. The investment is also subsidized and the expenses can be deducted from taxes. The only problem? Lack of political support. “Claudia Roth from the Greens once said to me: ‘Thermal insulation is not sexy, Mr. Drewer'”, criticizes the insulation expert.
ntv.de: You are angry with the traffic light coalition in Berlin. Why?
Arnold Drewer: The general energy situation is well known. I’m slightly sour because the public discussion is all about how we can buy energy, hard coal or LNG. How can we promote heat pumps? They are quite good, but only in well-insulated houses. On the other hand, I hardly ever hear or read the terms “energy efficiency” in general and “thermal insulation” in particular.
Are you bothered by the fact that high prices are depressing and citizens are being relieved, but no one is thinking about how energy consumption can be reduced?
That’s the way it is. There is this proposal for gas price relief for EUR 96 billion. A scientific study commissioned by us as the Blown-In Insulation Association came to the conclusion: This money would be enough to save about a quarter of the German heating energy in Germany. So you could give the citizens a 25 percent energy consumption measure that doesn’t last for a year or two, but for 50 or even 100 years – depending on how long the house is standing. Of course, you have to help the poorer population with their energy costs, but cheap insulation measures would also be really sustainable in the interests of taxpayers. I have explained this in several letters to the relevant ministers, party and faction leaders of the traffic light, but I have never received an answer. That’s why I’m angry.
How does blow-in insulation differ from other thermal insulation?
The normal person understands thermal insulation as the thermal insulation composite system. Insulation panels are glued or screwed to a wall on the outside. Then the whole thing is plastered, the house looks brand new. But this is a complex and expensive process. It currently costs between 30,000 and 40,000 euros for a single-family house, depending on the size. Three journeymen painters work on the facade for two to three weeks.
With my IPEG institute, however, I have identified 75 procedures for the old building. These methods include 31 structural situations where the building has a hollow core and is eligible for blown insulation. A common example is the wall: I have an interior wall with wallpaper and pictures and an exterior wall. In between there is a hollow layer five to ten centimeters thick.
Why was it built like this?
This was invented in the 19th century to deal with moisture problems. A wall that actually consists of two walls cannot transfer water from the damp outer wall to the inside. This type of construction is mainly found where the wind and rain come from the front: in Northern Germany, Benelux and the Netherlands. That’s called heavy rain. 80 percent of the houses there are built like this. Almost every one in Schleswig-Holstein, but there are also many in Hamburg, Bremen, Lower Saxony and North Rhine-Westphalia. The further south we go, the fewer there are.
Because the rain tends to fall from above there?
Exactly. Across Germany, 30 percent of houses have such a hollow layer, which can be insulated extremely cheaply and easily: holes are drilled into the wall according to a specific pattern. A hose is placed on the holes and the insulating material is transported into the wall by means of air pressure, so the hollow layer is blown out. Then the hose comes away again, the wall is closed. Two people don’t even need a whole day for a normal house. And because the labor costs are so low and we don’t need any scaffolding or anything like that, the blowing-in procedure costs between 3,000 and 4,000 euros. For the sake of honesty, however, one has to say that the thermal insulation composite system is not only ten times more expensive, but also better than core insulation because it can be made 16 to 20 centimeters thicker. So for 30,000 to 40,000 euros I can save 30 percent on heating energy. With a low-investment insulation process for a tenth of the sum but also about 20 percent.
That sounds sensible, but isn’t it done?
But already. But only from the people who know it. I live in Paderborn. We have about 20,000 single-family homes here that would be eligible for the process. If it comes up, I estimate a maximum of 500 of these buildings are insulated as advertised. 19,500 houses still have an uninsulated hollow layer and consume a lot of energy through the wall.
How is it in Germany? You spoke of 30 percent of the residential buildings.
In the study we commissioned, the Hessen Energy Institute estimates that around 30 percent of 19 million residential buildings in Germany would be suitable. The Research Institute for Thermal Insulation (FIW) in Munich, too. That would be six to six and a half million houses. The same applies to non-residential buildings. Schools, hospitals and kindergartens have often been built in this way.
How many of these six million buildings can still be insulated?
You can still do that for about three and a half million buildings. I come from practice. The procedure has been known for more than 50 years, I did it myself 30 years ago. I estimate that I am responsible for about 5,000 of the two and a half million buildings that have already been insulated in Germany. And I haven’t had a single building physics error where people said: I have mold or something like that. Not once.
And with these three and a half million houses, one could ultimately save a quarter of German heating energy?
no There are more than 30 blow-in insulation situations in old buildings. The hollow layer in the wall is the most common, but only one of them. There is also the upper floor, the “forgotten” part. This is the last ceiling of the inhabited and heated space in the building. Above that there is usually only the unheated attic where old furniture, toys and such things are stored. 75 percent of these ceilings are wooden beam ceilings, i.e. covered with wooden boards from above. If you drill into these boards, you will often find a hollow layer of up to 18 centimeters, which you can also fill with this very simple procedure: put in the hole, put on the hose, blow out, close the hole.
Suppose you close the cavity in the wall and also in the ceiling. By how much does energy consumption drop then?
That should be about 30 percent. Of course, that depends heavily on the cubature of the building, i.e. the volume. In a very tall building, such as a four-story apartment building, the top floor is very small in relation to the building as a whole. In a bungalow it is exactly the opposite.
Does this mean that this method is not only suitable for single-family houses?
Right. In East Germany in particular, we very often have two-shell flat roofs – not with private builders, but rather in the housing industry. With these roofs, I look down at a concrete ceiling on the top floor. A cavity of up to 50 centimeters high was deliberately left above this concrete ceiling. Above that is the actual flat roof with bitumen sealing and so on. You can also drill into it and fill it with blow-in insulating materials.
What kind of material is actually blown in there?
Very different depending on the application. In the case of the double-leaf masonry, the materials must be hydrophobic, i.e. water-repellent. They must not transport the driving rain from the outer wall to the inner wall.
And that looks like cotton or wool?
It looks like cotton, feels like cotton, but is glass. A mineral recycling product. However, this only applies to the double-leaf masonry. Cellulose is more likely to be used for the wooden beam ceilings because it is assumed that condensation forms under the wooden boards on which the old furniture and other stuff is standing. Cellulose is an insulating material based on newspaper and is also a recycled product. This paper can absorb the moisture that accumulates in winter and release it again in the dry period, i.e. in spring, summer and autumn.
Is there a solution for every building situation?
Yes. We have more than 100 different insulating materials in Germany. Ten of these are different blow-in insulation products. The rest is sheet goods, mat goods and so on. This can be used to solve any structural situation and even to improve or optimize any component in terms of energy.
But why are these methods so rarely used? That sounds a lot more sensible than putting up expensive relief packages every year when things are going badly.
I do not understand that, too. In any case, this is not the international rule: In France, the insulation of the upper floor ceiling is subsidized by 50 percent. People who have a low income even pay only one euro.
One euro? Symbolic?
Exactly. In the Netherlands, the core insulation of double-leaf masonry is also subsidized at 30 percent. I don’t know why they don’t do that in Germany. I’ve been on Twitter lately and I’m sharing it there, a little sarcastically: Dear politicians, thermal insulators aren’t pimps! Because sometimes I really have the impression that the topic often has negative connotations: thermal insulation is on fire, the house is moldy, I can’t breathe and so on. None of these statements are correct, but they persist in the population. These assumptions seem to have spilled over into politics. After all, politicians are actually normal people with their own ideas, thoughts and prejudices. Claudia Roth from the Greens once said to me: “Thermal insulation is not sexy, Mr. Drewer.” This is a literal quote.
Not even the Greens deal with the topic?
no The Greens only talk about renewable energy, photovoltaics and wind. Maybe it’s because of the genesis of the party, the Greens come from the anti-nuclear movement. That’s why I want to set up my own guide with the Ipeg Institute. From December, 55 insulation situations will be described on www.daemmatlas.de, which we hope everyone will understand. This not only includes blow-in insulation, but also do-it-yourself measures such as insulating roller shutter boxes, attic stairs or basement ceilings.
And to say it again very clearly: The industry doesn’t need money, but public relations so that it can plan in terms of personnel and machines. The investments are only worthwhile for small companies if they know that they will have something to do next year or the year after that. It would probably be enough if Mr. Habeck or Mr. Scholz said on television: Guys, insulate your houses!
How quickly did the costs of 3,000 to 4,000 euros pay for themselves?
With the current energy prices, you can get them out in four years. These procedures are all funded by BAFA with 15 percent, but you need an energy consultant for this. For two and a half years, however, these measures have also been able to be deducted from income tax very easily and unbureaucratically. You don’t have to apply, you don’t have to wait for approval from BAFA. This also applies to thermal insulation composite systems and new windows.
And who do you contact if you are interested in blow-in insulation or if you want to find out if your home has a cavity between the walls?
You can actually do it yourself, for example by drilling a hole in the wall from the outside. If the drill eventually jerks or hits forward and disappears, there is a cavity. If you don’t want to do it yourself, contact an energy consultant. I found the chimney sweeps to be particularly competent, because they are out and about in almost every German house almost every year because they have to check the heating systems. They also go into the basement as part of their job, can look at the basement ceiling there and are on the move on the upper floor ceiling. Chimney sweeps also have an endoscope with them. Not as expensive as at the internist’s, but sufficient to look into hollow layers.
