Status: 11.10.2023, 16:20 PM
By: Vivian Werg
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In the cooler seasons, thermal insulation brings several advantages. However, if you are badly advised, it can quickly become a price trap.
Berlin – Good thermal insulation (external thermal insulation system) for the house helps to save energy. According toco2online.de, the better a house is insulated, the more heating energy can be saved. However, Building Minister Klara Geywitz (SPD) questioned whether thermal insulation is really the best method for climate protection.
But homeowners are often faced with the challenge of finding good and reputable companies. Often, they are not only badly advised, but also confronted with prices that are difficult to understand. ZDF's consumer magazine WISO took a closer look at companies and made appointments with four different companies – with frightening results: only one company makes a professional recommendation.
Effective thermal insulation can save a lot of heating energy (symbolic image) © Angel Santana Garcia/ Imago
ZDF-Wiso: Which materials are suitable for thermal insulation
The test is about a house that was built in the 1930s and renovated in 2015. "You are not obliged to have your house insulated. Only if you renew the plaster do you have to work in accordance with the Building Energy Act," explains energy consultant and expert Andreas Lippertz. According to the expert, if you insulate the house, you have to pay attention to the following:
- At the bottom of the plinth area: The plinth does not end at the basement ceiling, but above it.
- Thermal bridge is created: If the insulation is not deep enough, there will be temperature differences between the insulated and non-insulated parts. This can quickly cause mold.
- Cost: between 40,000 and 50,000 euros
According to the energy consultant, you can use Styrofoam or mineral wool for insulation. But also use hemp or jute. "As a rule, however, houses are insulated with polystyrene. That would also be perfectly fine with the house," Lippertz continues. However, if you have increased requirements for fire protection, mineral wool is used, but it is much more expensive. The consumer advice centre provides helpful tips on how to plan thermal insulation correctly.
ZDF-Wiso reveals: Three out of four companies have no technical competence
Three out of four companies advise on a variety of topics, but not on thermal insulation. For example, the first craftsman primarily advises on sealing rather than on the external thermal insulation composite system. He also doesn't say a word about the façade and also advises against insulating the basement ceiling "because the basement is not inhabited". In the end, he recommends an insulation of 10 cm. He estimates these costs at 20,000 euros, plus scaffolding work and VAT. In the end, the offer amounts to a total of 50,000 euros.
"He has no idea what he's doing. 10 centimeters of insulation is not enough for polystyrene. With this insulation thickness, it does not meet the legal requirements," says Lippertz.
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Energy consultant annoyed: "There is zero competence"
Non-transparent pricing and a lack of expertise are also uncovered at two other companies. One craftsman provides extensive advice on blown-in insulation, which is suitable for so-called double-shell masonry, for example. In other words, if the wall consists of two parts and there is a layer of air between them. This insulation can be blown in. The house, however, was a single-shell masonry with a one-piece wall. Again, basement insulation is not recommended. In the end, this incorrect advice cost 220 euros. In the end, they waited in vain for a written offer.
The other craftsman comes together with the site manager. But even in doubles there is a lack of any expertise. When asked whether the house needs to be insulated, reference is made to the energy class. The site manager also refers to an energy consultant on the subject of fire protection and which material is recommended. "Only a poor energy class, does not oblige to thermal insulation. There's zero competence there," says expert Lippertz angrily. "Everything is passed on to the energy consultant." In addition, they were unable to provide a cost estimate on site. Later, the written offer only includes the cost of the work, but does not include the cost of materials. The costs amount to 36,000 euros.
ZDF-Wiso: Only a craftsman gives a professional recommendation
Only a craftsman is able to explain the different insulation systems. He also identifies all problematic areas of the house and offers suitable solutions. Particularly pleasing: He would install basement ceiling insulation and insulate the façade insulation up to the basement ceilings.
Finding good companies is certainly not easy. Andreas Lippertz advises asking friends and acquaintances. You can't go wrong with a newly insulated house and just ask – because it doesn't cost anything to begin with. (Vivian Werg)