Wall, roof, window, heating: This is how the house becomes an energy-saving house

The subsequent insulation of older houses or apartments is now a science in itself.

Wall, roof, window, heating: This is how the house becomes an energy-saving house

The subsequent insulation of older houses or apartments is now a science in itself. Whether external facade, window roof or basement - the variety of technical possibilities and materials is enormous. Since 2020, anyone who wants to make more than ten percent of the building energy-efficient has to consult an energy consultant. The consultation ranges from the first meeting, through the on-site building check, to the individual renovation schedule. Depending on the size of the house, the costs are between 1700 and 2400 euros. The Federal Office of Economics and Export Control BAFA supports the consultation with up to 1700 euros. Anyone who hires the energy consultant as a so-called construction supervisor for the implementation will be reimbursed half of the support costs by BAFA. The construction supervisor not only monitors the work, but also certifies that it has been carried out properly. Funding is only available with these certificates. The "Renovation Configurator" from the Federal Ministry of Economics gives a first impression of the savings potential of a renovation.

Buildings account for about a third of the energy consumption in Germany, which corresponds to about 115 million tons of CO2. This amount of greenhouse gases is to be reduced by 40 percent in order to achieve the EU climate protection targets for 2030. Since November 1, 2020, the GEG has implemented the EU requirements into national law. It specifies the insulation, heating and air-conditioning technology and the proportion of regenerative energies for heating and cooling for new and existing buildings.

While new buildings are planned in any case in an energy-efficient and sustainable manner, the GEG primarily calls for the refurbishment of existing buildings. The focus is on oil and gas heating systems. Basically, if a heater is more than 30 years old and works according to the principle of constant temperature technology, it must be replaced. Oil and gas heaters of recent years with low-temperature and condensing technology can stay in. If you are not sure, you can ask your chimney sweep.

Owners of detached and semi-detached houses who lived in their property before February 2002 can relax. They are largely exempt from replacing their heaters. Anyone who bought or inherited a property after February 2002 must renovate it within two years in order to meet the requirements of the GEG. Even if you are over 80 years old, as of 2023, you do not have to change anything about the property you use yourself.

In the long term, however, all property owners have to deal with the issue of heating. By 2045 at the latest, all heating systems powered by fossil fuels should have disappeared. In order to benefit from the sometimes high subsidies, renovations should not be postponed too far into the future. If the replacement of the heating system is required by law, for example if the heating system has been in operation for more than 30 years, there are no longer any subsidies!

The GEG requires a U-value of 0.24 for the outer wall insulation, which corresponds to an insulation material thickness of at least 12 - 16 cm.

New heaters operate at significantly lower temperatures than their predecessor systems. Therefore, in old buildings, the new heating alone is often not enough, its output would not be able to counteract the heat loss due to poor insulation in winter. It doesn't work without insulation.

After the insulation of the outer walls, the roof insulation is the renovation with the greatest effect. About 30 percent of a house's heat is lost through the exterior walls. The extent of the heat loss is determined by the structure of the wall and the so-called thermal bridges, structural areas through which heat is dissipated to the outside particularly well. Façade insulation is always worthwhile for owners of older houses built between 1960 and 1980. However, the costs are considerable because of the large area, the material requirements and the scaffolding work. Even if energy prices continue to rise, it will probably be decades before the heating savings exceed the investment. External wall insulation should not be reduced to the savings. Insulated exterior walls noticeably improve the living environment. In winter through less cold inner walls, in summer through less heated ones. The insulation also protects the facade, the renovation of which is due at some point in every house. Good insulation also increases the value of the property. Older houses with good thermal insulation should sell better and at a higher price in the future than uninsulated ones.

The GEG requires at least a U-value of 1.30, i.e. the insulating window with two panes.

A house loses around 20 percent of its heat through the windows. The good news: a lot has happened in glazing in recent years. The U-value shows how well a window insulates. The smaller the value, the less heat escapes to the outside via the window surface. The U-value is 6 for single glazing, between 1.1 and 1.4 for double glazing and between 1.1 and 0.7 for triple glazing.

A bill from the consumer advice center shows how enormous the effects of heat-insulating glazing are. In the scenario, the inside temperature is 20 degrees Celsius and the outside temperature is -10 degrees: With a single-glazed window, the inside of the window would be -1 degrees cold, with double insulation 10 degrees, with thermal insulation glazing 15.7 degrees and with triple thermal insulation glazing 17.3 degrees. Even modern windows can save between 10 and 20 percent of heating costs. The U-value refers to the entire window, not just the glazing. A U-value of 1.10 is required for the window glass. A nice side effect of modern windows: better noise insulation.

In new buildings, roller shutters are part of the overall concept of building insulation. Not only do they make the work of burglars more difficult, they also effectively inhibit heat loss after sunset and keep the interior cool in summer. Roller shutters can be retrofitted for homes and apartments. Either in a box on or in the outer facade or, if space is available, in a box above the window in the interior. Both should be installed by specialist companies. Roller shutters installed outside have the greater cooling effect in summer because the sun cannot heat up the window panes. Insulation is important for internal boxes in order to avoid thermal bridges. Advantage of roller shutters: little effort, sophisticated technology, multiple benefits.

Front doors and patio doors can be real heat dissipators. Especially if they are 30 years and older. The seals have weakened, the heat protection of the front door is far removed from today's standards due to old glass elements, for example, or thermal bridges have arisen due to the type of installation. As with windows, thermal insulation for doors is also given in the U-value, more precisely in watts per square meter in Kelvin. The thermal transmittance value expresses how much heat passes through any barrier between two rooms when the temperature difference in both rooms is 1 degree Kelvin. Nothing to remember, except for one thing: the lower the U-value, the better the insulation.

The GEG requires a U-value of 0.24 for the outer wall insulation, which corresponds to an insulation material thickness of at least 12 - 16 cm. Skylights must achieve a U-value of 1.40 and have thermal insulation glazing.

Knowing the GEG also regulates the specifications for energetic renovations of roofs and attics. Up to 30 percent of the heat in the house would escape through an uninsulated roof. Houses from 1950 to 1980 with their undeveloped attics, crawl spaces and flat roofs are particularly affected. Roof insulation from the inside is already available for around 40 euros per square meter and can be carried out by a skilled do-it-yourselfer. The material is applied between or on the rafters. Under-rafter insulation, where the roof has to be covered, is significantly more expensive and can only be carried out by a roofer. Advantage: There is much more space inside. The vapor barrier has to be worked on very carefully. Vapor barriers are robust foils. They protect the material from penetrating water vapor that occurs when cooking, showering and even breathing. If the film is not applied 100 percent accurately, water vapor will penetrate through the gaps and settle in the insulating material. Consequence: mold.

The GEG requires a U-value of 0.50 for ceiling insulation in an unheated basement

The effort and costs of basement insulation depend on how it is used. If the basement is unheated and is only used as a storage room, insulating the basement ceiling is sufficient to prevent the floor on the ground floor from cooling down. If the basement is already low, the insulation will finally turn it into a "bend cellar". To maintain the full basement height, insulation can also be applied to the ground floor floor. A complex affair with follow-up costs. Even if the insulation is thin, all doors must then be brought up to the new level. New tiles are needed for the kitchen and bathroom. Anyone who is actually considering this should think about installing underfloor heating right away. This fulfills the insulation downwards and at the same time the radiator system favored by most heat pumps.

The GEG requires a U-value of 0.30 for wall insulation in an unheated basement

In heated basements, wall insulation prevents heat loss and ensures a better living environment. Interior insulation is cheap and easy. However, it has two disadvantages: the living space becomes smaller and the risk of mold forming behind the insulation increases. Mold forms when moisture in the air condenses on the coldest part of a wall. The warmer the air, the more water it can absorb in gaseous form; when the temperature drops, the water vapor condenses as moisture. The temperature at which this happens is called the dew point. If the dew point is at the same level as the insulation, there will be mould. Perimeter insulation is more effective but significantly more expensive. The house is dug up all around to attach the insulation made of polystyrene or polyurethane rigid foam panels. Both prevent moisture from penetrating the basement walls. A worthwhile effort for anyone who wants to use their basement as additional living space. However, the costs can quickly run into the tens of thousands of euros. If you dare, you can do the earthwork yourself and save a lot of money. However, basement insulation should be at the end of the list of all other energy-related renovations.

With this form of insulation, loose insulation material is filled into cavities with a hose under air pressure. There are many such cavities in older houses. In northern Germany, for example, the outer walls often consist of a sandstone inner wall with a brick facade and a cavity in between. Cavities can also be found in pitched and flat roofs, the attic, sometimes also in the ceilings. The larger the cavity, the greater the insulating effect. For effective insulation of the outer wall, the cavity should be at least three centimeters wide. Where there is no cavity within the house, one can often be created by boarding. Blown-in insulation costs only a third of other insulation techniques. Disadvantage: It is not always possible, especially with expensive external facade insulation.

The house is insulated, significantly less heat escapes to the outside. Time to cut heating bills and turn down boiler output. But then the old ribbed radiators no longer want to get really warm. The big old radiators need a lot of water to heat up. However, the reduced output of the boiler is no longer sufficient for this. On average, new radiators require up to two thirds less heating water for the same output and they also react much more quickly to inputs on the thermostat. Anyone who converts their heating system to a heat pump or solar thermal system also needs modern radiators because the old ones cannot cope with the lower temperatures of these systems. Positive side effect: A new interior design with space gain. The clunky old radiators used to be placed directly in niches under windows. Such corners are classic thermal bridges, through which a particularly large amount of heat is dissipated to the outside. Conceived at a time when energy didn't cost much. Modern radiators are much flatter, can even be installed upright and become part of the wall. They also ensure a more pleasant room climate, as they radiate heat in a targeted manner and do not just heat up and dry out the air like their ancestors did.

According to GEG, they too will be standard in the future: Separately programmable thermostats for each room. There is a wide range of options and you can do the installation yourself. As a Smart Home variant, the thermostats can even be controlled via an app, even when you are out and about or on holiday. This turns the “stupid” radiator into a halfway smarter one. They regulate themselves down when you leave the apartment and up again a little before you return, so that the apartment is already warm when you arrive. Practical for apartments, also as a tenant. Modern heating systems for single-family homes have their own digital control systems anyway, which can be used to program the heating.

At the latest since the amendment of the Building Energy Act GEG in March 2023, homeowners have been alarmed. Even if the originally planned general ban on oil and gas heating from 2024 is off the table: Anyone who currently has such a heating system in the basement should familiarize themselves with an environmentally friendly replacement. The alternatives are heat pumps, heat pump hybrid systems with oil and gas, gas heating with biomethane, biomass in the form of pellets and district heating.

District heating would be the simplest option, but requires a connection to the district heating network. Even if a corresponding line is nearby, it must have the power required to supply other households. Only around 14 percent of all buildings in Germany are currently heated with district heating. The connection requires earthworks and can quickly cost tens of thousands of euros.

Biomass (pellets) is still allowed, but not an option in the long term. The federal government will severely limit the burning of wood, among other things because of the fine dust pollution, and will hardly promote such systems. In combination with a solar system, heat pumps are an effective green alternative and the one favored by the federal government.

The heat pump is currently the "greenest" form of heating the house. And it's tried and tested. In Norway, a good 600 out of 1,000 households heat with this technology, in Sweden it is practically the standard heating system for single-family homes. In densely built-up Germany, the large heat exchangers could cause headaches for some homeowners and owner associations, for example of old terraced houses. Heat pumps obtain the heat either from the air, the ground or the groundwater. Which source is suitable depends on the location of the house.

Either way, in most cases there will be a heat exchanger the size of a chest freezer at the house. A fan rotates in the exchanger with a noise level of around 50 decibels, which roughly corresponds to soft radio music. Noise-sensitive people already perceive this as disturbing. The neighbors may only get 35 decibels of this, which is why a distance of three meters from the property line is required.

At the same time, the heat pump should be close to the house, but not in the vicinity of bedrooms, but should be close to the energy source used. The performance of the pump must be matched to the building. If the dimensions are too small, the house will not warm up, if it is too large, the operating costs will increase.

Even if the pump draws its heating energy from the environment, it needs electricity to operate. A twelve kilowatt system around 6000 kilowatt hours per year at an electricity price of 40 cents costs around 2,400 euros per kilowatt hour. If you have the appropriate roof area, you should have a power-generating solar system calculated and generate your own electricity for the heat pump. Since heat pumps work at significantly lower temperatures than oil and gas heating, an energetically renovated house is a basic requirement. Otherwise it could get chilly inside in cold winters or the electricity bill high.