Hausbau: How much energy efficiency should it be?


Berlin – The legal requirements for the energy efficiency of new buildings have been increasing for years. But it can also do more. How far should you go?

News / Gas

Picture: Energy efficiency in building a house

The current specifications correspond to the standard of the Efficiency House 70, which has been funded by KfW-Bank since 2009. These new guidelines for residential buildings now provide the Energy Saving Ordinance (EnEV).

Only more efficient buildings will be supported in the future

“The EnEV has reconstructed what the KfW funding has anticipated,” says Christian Stolte of the German Energy Agency (dena). KfW will discontinue KfW’s funding for the Efficiency House 70, which thus complies with the statutory minimum standard, by the end of March. Then, in addition to the existing standards Effizienzhaus 55 and 40, the Efficiency House 40 Plus will be introduced instead. In these buildings, a large part of the energy demand is generated and stored on or in the house.

How much is useful?

But what do these steadily stricter guidelines mean for builders? The consumer center NRW warns that houses, which are built today according to the EnEV standard, can be outdated shortly after completion of construction. She therefore advises to build already higher efficiency standards. A passive house can handle about half the energy allowed by the new EnEV. “It pays to do more,” says dena expert Stolte. But that depends on the financial possibilities of the builders. “It is certainly not a mistake to build only according to the specifications of the EnEV.”

Savings are not linear

If you build according to the current standards, do not do anything wrong economically, says Dietmar Walberg from the Working Group for Contemporary Buildings in Kiel. “Whether you do more is often an ideal question, and one of the purse.” After all, the additional expenditure does not always pay off in the energy saved. An efficiency house 40, which has only 40 percent of the primary energy requirement of the current EnEV standard, does not save 60 percent in comparison. “That’s not linear,” explains Walberg. A quarter to a third less energy costs a year, according to the expert in the case is rather realistic. “That should be clear, but is no reason not to build more efficient anyway.”

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Are there any stricter requirements?

But what about the warning from the consumer center: Is the house quickly outdated building technology, if you build according to the EnEV? “The EnEV has always formulated a standard that still left room for improvement,” explains Alexander Lyssoudis of the Bavarian Chamber of Civil Engineers. The EnEV describes the border to the upper third of what is actually possible. He also advises to go beyond the requirements of the EnEV, if it is financially possible.

It is difficult to predict if the regulations will become even stricter in the future. On the way to the European lowest energy standard, which should apply in 2021, this can not be ruled out. On the other hand, concrete requirements of the European Union are not yet known, says Lyssoudis. Whether the standards get even sharper again depends on the products. If the demand for efficient building materials becomes more affordable or new innovations come onto the market, this can lead to a tightening of the guidelines.

Limits of economy and physics

Insulation, plant efficiency – all of the requirements of the EnEV are currently reaching their economic limits, Walberg explains. This means? “These additional costs are no longer brought in by the energy savings in a reasonable time frame.” With that logic you can not get any further, he says referring to possible tightening of standards in the near future.

Structural thermal protection is currently reaching its physical limits, says Lyssoudis. “On the other hand, new standards often give a special boost to new developments in building materials.” The new KfW Höchststandard 40 Plus is already heading for the plus energy house. As a rule, there is a photovoltaic system for power generation there, very rarely there are according to Walberg wind turbines or biogas plants. In this highest funding category, 15 percent of the construction costs are financed by means of a repayment subsidy.

Plus-energy houses produce energy but do not necessarily earn money

The plus energy house goes even further. Here, the primary energy balance over a year seen positive. You save energy costs and still take money, you might think. But this bill does not quite work, as Lyssoudis explains: “You save money in any case, but you will not make money with such a house yet.” For sun does not seem year round. Since the technology of storage is not far enough to store electricity in the long term, one must also use energy from external sources, explains Lyssoudis. However, whether the power supply is worth it, depends on many factors, adds Walberg. Is there enough sunshine due to the location of the house? Is the roof area big enough for the photovoltaic system?

What will the future bring?

In the future Walberg also considers other concepts conceivable. “Houses will eventually network.” Instead of energetically optimizing each building to its limits, houses generate energy in different ways and provide each other with energy. Another ecologically sensible future option is having to plant a certain number of trees per house to offset climate-relevant emissions. But regardless of all current and future standards, you can be green on a small scale. Walberg: “Anyone who builds regionally and prefers building materials from the region for his house, makes something useful for the environment.”