Energy-saving building - the airtight building envelope
Due to the increasing scarcity of fossil fuels, the goal of saving energy is becoming more and more important. Energy-efficient construction is considered an important measure for achieving this goal. It was first introduced in 1976 during the oil crisis through the Energy Conservation Act and later developed further in the Energy Conservation Ordinance (EnEV). Today, it has been replaced by the Building Energy Act (GEG), which bundles all requirements for the energy quality of new and existing buildings. The following article explains exactly what is meant by the term “energy-efficient construction,” how great its benefits and potential are, and what specific measures result from this term.
Guide topics:
- Why is energy-efficient construction worthwhile?
- Benefits and potential of energy-efficient construction
- Parameters and specifications for energy-saving construction
- Consideration of individual components
- Modern building services as a complement to energy-efficient building envelopes
- Subsidies
- Conclusion
- FAQ: The most frequently asked questions
Why is energy-efficient construction worthwhile?The advantages of energy-efficient construction at a glance
What does energy-efficient and climate-friendly construction mean?
Energy-efficient construction aims to reduce a building’s energy requirements as much as possible. This is achieved primarily through a highly insulated, airtight building envelope that significantly minimizes heat loss through masonry, windows, roofs, floor slabs, and joints. A good building envelope thus forms the basis for low heating costs and at the same time protects against moisture damage.
The aim is not only to save energy, but to operate a building completely without fossil fuels. Ideally, the house even generates more energy than it needs for heating, hot water, and ventilation—in other words, a plus-energy concept.
A key role is played by the building’s own electricity production, usually via a photovoltaic system. This enables building services such as ventilation, hot water preparation, and modern heating systems to be operated entirely on electricity and, when using renewable energies, fossil-free. Climate-friendly construction thus combines the classic energy-saving building envelope with a holistic energy concept based on efficiency, own electricity use, and sustainable building services.
Benefits and potential of energy-efficient construction
Private households offer great potential for energy savings, as 82 percent of energy consumption in private households is accounted for by heating and hot water production. Around two-thirds of total energy consumption in private households is accounted for by space heating alone. In order to exploit this potential, the demands on the construction industry are increasing. These mainly relate to more airtight construction through better insulation of masonry, windows, roofs, floor slabs, and joints.
This is referred to as “airtight construction,” which is designed to prevent energy and heat loss. However, a high-quality building envelope not only creates the basis for an energy-efficient building, but also enables climate-friendly and even climate-neutral concepts. Thanks to the significant reduction in heating load—especially in combination with a ventilation system with heat recovery—modern building services can operate much more efficiently. However, it is not only new buildings, which usually only require a quarter of the heating energy of existing buildings, that offer a great opportunity to conserve fossil fuel reserves and reduce energy consumption. Looking only at the energy consumption of existing buildings in Germany, the considerable savings potential offered by building renovation is also easy to see.
In addition to saving energy and conserving fossil resources, energy-efficient construction also offers a cost advantage. The significantly lower heating load not only reduces annual operating costs, but also opens up the possibility of using low-maintenance, durable, and resource-saving building services in the long term.
Energy-efficient construction not only reduces future consumption, but also lays the foundation for building services that are simpler, potentially more durable, and more sustainable in terms of resource conservation. This shifts the focus from energy consumption during operation to what is known as gray energy. This includes the energy already used for the manufacture, transport, installation, and subsequent replacement of building materials and building services. The lower this hidden energy consumption and the more durable the components used, the more sustainable the entire building concept is: from the first component to the entire life cycle.
What are the specifications and parameters for energy-efficient construction?What you should bear in mind if you want to build in a climate-friendly way
How can the components be compared with each other? – The U-value
All components are made comparable using the U-value. This value indicates the heat flow (measured in watts) that passes through one square meter between the interior and exterior walls at a temperature difference of one Kelvin. This results in the unit watts per square meter and Kelvin, or W/(m²K) for short. The lower the U-value, the better the thermal insulation and the lower the heat loss of the component.
What does the GEG stipulate?
With the help of the U-value, the GEG (Building Energy Act) has set stricter requirements for the individual components of a building. As a result, only certain components that comply with the prescribed U-values may now be used in renovations or new buildings. For exterior walls, for example, the U-value for new buildings according to the GEG is a maximum of 0.24 W/(m²K). However, it is up to the energy consultant or architect to decide which measures are taken to comply with this value. Specifications and measures such as those for exterior walls exist for almost all component groups of a building. If the GEG specifications are met in their entirety or if a corresponding renovation project is planned, this may be eligible for funding, e.g., by the KfW (Kreditanstalt für Wiederaufbau).
Energy demand as a key indicator of energy efficiency
Another parameter used in energy-efficient construction and by the GEG is final energy demand. This is measured in kilowatt hours per square meter per year, or kWh/(m²a) for short. As with the U-value, the lower the final energy demand, the more energy-efficient the building is. This parameter is best known from the energy performance certificates issued for real estate. Nowadays, the energy-related information on this certificate must even be included in newspaper advertisements in order to create transparency for the end customer. When planning a residential building today, a number of factors must be taken into account:
Energy performance certificate according to GEG: Comparability and validity
If an energy performance certificate is used to compare energy consumption, it will include the primary energy demand. This value is expressed in kilowatt hours per square meter per year (kWh/(m²a)) and is often also represented on a color scale ranging from green (low energy demand) to red (high energy demand). The primary energy requirement takes into account not only the actual energy consumption in the building, but also the upstream energy expenditure for the provision of the respective energy source.
Since the Building Energy Act (GEG) came into force, the requirements for buildings have been standardized and the previously separate regulations (EnEV, EnEG, and EEWärmeG) have been merged. This makes energy performance certificates more comparable today, provided they have been issued in accordance with the GEG. Nevertheless, when comparing different buildings, it is important to note when the energy performance certificate was issued, as older certificates may still be based on previous legal requirements. An energy performance certificate is valid for ten years. Therefore, there may still be valid energy performance certificates in circulation today that are based on older calculation methods and present energy performance values differently than current certificates issued in accordance with the GEG. For a realistic assessment of a building’s energy efficiency, both the reported key figures and the date of issue of the energy performance certificate should therefore be taken into account.
Consideration of individual componentsSpecifications and measures for energy-saving masonry
Orientation and zoning of a building
The orientation and zoning of a building refers to the alignment of rooms according to the cardinal directions. It is worth placing rooms with low heating requirements, such as bedrooms and staircases, on the north side. The south and west sides benefit from long hours of sunlight, which is why it is advantageous to place the living room on these sides. If, for example, the living room is on the north side, not only does it require a lot of heating, but the lights also need to be turned on earlier.
Specifications and measures for energy-saving masonry
Masonry constructed in the past has a U-value of up to 2.2 W/(m2K). Such a high value results in high energy loss. Masonry can be retrofitted with a 16-centimeter-thick composite thermal insulation system. The improvement in heat loss is between 29 and 41 percent from various perspectives, even without taking into account the changed thermal bridge allowance.
Other quality characteristics include thermal conductivity and the classification of bricks according to their bulk density. As mentioned above, the maximum U-value for exterior walls of residential buildings is 0.24 W/(m2K). Looking at the data sheets provided by manufacturers of various wall element structures, it is clear that the industry is developing in line with political requirements.
Most manufacturers provide wall elements that already meet GEG requirements without additional insulation. These can be hollow bricks, for example, in which the cavities are filled with insulating material. A second variant is aerated concrete blocks, in which the bulk density is reduced by using lightweight mortar.
In addition, exterior and interior plaster are also components of the walls. The market offers special types of plaster for every need, such as thermal insulation plaster, water-repellent plaster, and synthetic resin plaster, which are usually used together as base or top coat plaster. These can have different thermal conductivities and thus reduce the primary energy requirement.
In addition, exterior and interior plaster are also components of the walls. The market offers special types of plaster for every need, such as thermal insulation plaster, water-repellent plaster, and synthetic resin plaster, which are usually used together as base or top coat plaster. These can have different thermal conductivities and thus reduce the primary energy requirement.
Requirements and measures for an energy-efficient roof
Requirements and measures for an energy-efficient roof
In the past, insulation materials were poured into the false ceiling, the area between the attic and the floor below, to insulate the roof. Today, mineral wool up to 26 centimeters thick is used in false ceilings to keep heat loss to a minimum. To this end, it is particularly important that all layers, such as intermediate rafters, counter battens, and plasterboard, are installed professionally so that the vapor barrier can be installed in the roof without damage.
The previous thermal insulation regulations, the EnEV, and now the GEG have continuously increased the requirements for thermal insulation. These increasing demands on roof insulation also promote the construction or retrofitting of a tight building envelope. The target value U is 0.20 W/(m2K). Consequently, the same low heat loss should be achieved without bricks by using building components such as insulation wool and wooden rafters.
Requirements and measures for energy-saving windows
In 1977, the requirement for windows with aluminum and steel frames was a U-value of 3.5 W/(m2K). The GEG, on the other hand, specifies a maximum permissible value of 1.3 W/(m2K), without distinguishing between different window frame materials. A separate value of 1.1 W/(m2K) is specified for glazing. When purchasing windows, you should ensure that the frame and glazing together have a value of 1.3 W/(m2K). The air permeability of windows is now classified into classes 1 to 4 by DIN 12207, with class 4 representing the lowest level of uncontrolled air exchange.
Furthermore, the installation of windows and window sills in the masonry and the materials used for this purpose also play a major role in terms of airtightness. Drafts, which usually occur under the window sill, are a typical phenomenon in this context. These drafts must be avoided, which is why the need for controlled residential ventilation is becoming increasingly important.
The blower door test, also known as airtightness measurement, is used to detect and measure such draughts. For this test, the building is subjected to 50 pascals of negative and positive pressure using fans. This produces the n50 value, which shows how high or low the leaks in the entire building envelope are. The word “leakage” is synonymous with the word ‘leak’ or “hole.” If the construction project is subsidized by KfW, it is mandatory to carry out the test.
Modern building services as a complement to energy-efficient building envelopesWhy technology and building envelopes must be considered in conjunction with one another
Why is generating your own electricity an important component of climate-friendly construction?
A high-quality, airtight building envelope significantly reduces a house’s energy requirements. If this low residual demand is then covered by self-generated electricity, usually from a photovoltaic system, the result is a particularly efficient and climate-friendly building concept. Modern building services are increasingly electric, for example with the help of ventilation systems with heat recovery, hot water heat pumps, or alternative heating systems for low heating loads. Generating your own electricity makes it possible to cover a large part of your energy requirements directly on site, reduce operating costs, and operate the building more independently of fossil fuels in the long term.
Advantages of generating your own electricity (with photovoltaics) at a glance
High proportion of own consumption:
A large part of the annual electricity demand can be generated independently.
Lower operating costs:
Less electricity purchased, especially in the summer and transitional months.
Independence from fossil fuels:
The building services can be operated entirely electrically.
Climate friendliness
Self-generated electricity significantly reduces CO₂ emissions during operation.
Economic efficiency:
Due to the low heating load of modern buildings, photovoltaic electricity is used particularly effectively.
Future-proofing
High energy prices have a significantly lower impact on energy self-sufficient buildings.
Heating load and the role of ventilation: Why should ventilation and photovoltaic systems be considered together?
A ventilation system with heat recovery makes a significant contribution to further reducing the remaining heating energy. By recovering heat from the exhaust air, the heating loads in modern buildings can be significantly reduced, in some cases by up to two-thirds. This not only optimally complements the airtight building envelope, but also enables the use of smaller, more efficient building services. The lower the heating load, the easier it is to operate the building with self-generated electricity, especially in the transition periods and summer months.
What are the advantages of modern building services engineering over traditional systems?
Classic solution (e.g., heat pump + underfloor heating) | Modern electricity-based solution (e.g., infrared heating + ventilation + hot water heat pump) | |
|---|---|---|
Heating load requirement | Works even with high heating loads | Ideal for very low heating loads |
investment costs | Higher (heat pump, piping, underfloor heating, installation) | Lower (simpler components, no water-carrying heating circuits) |
Maintenance | Regular maintenance required (heat pump + water system) | Very low (infrared heating requires hardly any maintenance) |
Complexity of the system | High – many trades, many components | Low – few core components |
Power requirement | Efficient, but dependent on operating mode and outside temperature
| Low residual demand thanks to heat recovery + own electricity can be put to good use |
Use of photovoltaics | Possible, but not always optimal | Highly efficient: Electricity-based components make particularly good use of PV |
Grey energy
| High (lots of material, energy-intensive production) | Low (less technology, less material usage) |
Maintenance and service life of modern building services
Less maintenance required:
Electricity-based systems such as infrared heaters require very little maintenance, as they have no moving or water-carrying components.
Lower material consumption:
Simpler technology means fewer spare parts and reduced resource consumption over the life cycle.
Longer service life:
Many electricity-based systems generally have a long service life, as they are subject to less mechanical stress.
Less risk of failure:
Less complex heating systems usually mean less wear and tear and therefore less susceptibility to repairs.
Reduced operating costs:
Low maintenance and repair costs reduce ongoing expenses in the long term.
Sustainable overall balance:
Fewer maintenance trips, material replacements, and technical effort reduce gray energy over the entire period of use.
Can I receive subsidies for energy-efficient construction?
Depending on the measure, energy-efficient construction can be supported by government subsidy programs. A wide range of grants and low-interest loans are available, particularly in the area of renovation, while subsidies for new construction are currently more limited. Since subsidy conditions, budgets, and deadlines change regularly, it is worth checking early on whether the planned project meets the criteria for an energy-efficient house or for individual measures. Even if subsidies are not always available or suitable, energy-efficient construction can remain financially attractive in the long term due to lower operating and energy costs.
Conclusion
The requirements for building envelopes are becoming increasingly stringent. A building should allow as little air as possible to escape to the outside in order to prevent energy and heat loss. Regulations such as the GEG specify concrete guidelines for renovation or new construction, which are to be achieved through various measures. A tight building envelope also offers a significant cost advantage in terms of operating costs. The disadvantage arises from the lack of natural air exchange. This disadvantage can be offset by installing an automatic ventilation system. Decentralized ventilation systems in particular are suitable not only for new buildings but also for retrofitting existing buildings.
Frequently asked questions about energy-efficient construction
What does energy-efficient and sustainable construction mean in Germany today?
Energy-efficient and sustainable house construction means planning and building a house in such a way that it consumes little energy in the long term while also protecting the environment. This includes a high-quality building envelope, modern building services, efficient ventilation, and the most sustainable possible electricity production. The Building Energy Act (GEG) defines the most important requirements.
What are the advantages of an airtight building envelope in house construction?
An airtight building envelope reduces heat loss, lowers heating costs, and ensures that a house requires significantly less energy in winter. At the same time, it improves the indoor climate and protects the building from moisture damage in the long term. It is a key component of sustainable houses.
Why does ventilation play such an important role in modern house construction?
In very airtight houses, there is hardly any natural air exchange – which is why a ventilation system is necessary. A ventilation system with heat recovery provides fresh air, protects the building fabric, and reduces the heating load. This makes the planning of building services more efficient, as heating and ventilation systems can be optimally dimensioned, simpler thanks to the clear coordination of components, and more sustainable thanks to lower energy consumption and operating costs.
Is it worthwhile to generate my own electricity for my home?
Yes. A photovoltaic system makes it possible to cover a large part of your energy needs yourself—especially in homes with very low consumption. This makes your home independent of rising energy prices in Germany, improves your environmental footprint, and supports a sustainable overall concept in home construction.
Which building services are particularly useful for an energy-efficient house?
That depends on the heating load. In modern energy-efficient houses with heat recovery, the heating load is so low that electricity-based systems (e.g., infrared heating + hot water heat pump) are often sufficient. Traditional systems such as large heat pumps or water-based heating circuits can be oversized in very well-insulated buildings. Professional planning during house construction helps to find the right solution.
How sustainable is modern building technology in terms of maintenance and service life?
Modern, simple building services often require significantly less maintenance and have a longer service life. This reduces costs, material usage, and embodied energy. This is an important factor for sustainable buildings that are intended to be operated in an environmentally friendly manner for many years to come.
Where can I find reliable information on planning an energy-efficient house?
Anyone looking for information on energy-efficient house construction will find important basics and information at the Federal Ministry for Economic Affairs and Climate Protection, at energy advice centers, and at specialist companies for ventilation, insulation, and sustainable building services. Qualified energy advice is recommended for individual house construction projects.
How can I ensure that my house construction is sustainable and environmentally friendly?
Key factors are:
- High-quality insulation and airtight construction
- Ventilation with heat recovery
- Modern, electricity-based building services
- Own electricity production (PV)
- Durable and low-maintenance systems
- Holistic planning by experts
The result is a house that remains energy-efficient, economical, and environmentally friendly for many years to come.
What funding opportunities are available for sustainable house construction in Germany?
There are extensive subsidy programs for renovations (e.g., BEG, KfW). For new buildings, the options are currently more limited, but low-interest loans and individual subsidy programs can still provide support. Since programs change regularly, it is important to check early on which subsidies are suitable for your planned house construction.
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