10 common misconceptions about energy renovations

Mould growth is particularly related to high air humidity and insufficient ventilation, not to a good thermal insulation. 

In fact, insulation actually prevents the development of mould, as many examples of perfectly insulated, completely airtight, yet mould-free energy-efficient and energy-renovated houses show. If a dwelling’s exterior walls are insufficiently insulated, moisture in the air condenses in cold areas, which promotes the development of mould. A good thermal insulation of the facade ensures that the internal surfaces of the exterior walls remain warm, which prevents moisture from settling.

It is also important to identify and eliminate the thermal bridges (areas where the insulation is not continuous) in a building. These include, for example, radiator niches or balconies. In addition, it is recommended to avoid placing furniture onto exterior walls to allow air to circulate in the room and to prevent the surfaces behind furniture from cooling down. 

Draughty windows lead to insufficient and incidental ventilation and counteract the correct ventilation of a home. Adequate ventilation is achieved by opening windows or using a home ventilation system, whereas draughty windows cause heat loss and draughts on cold days. They thus contribute to an unpleasant room climate and unnecessarily increase heating costs. 

When renovating, it is recommended that new windows are installed by a specialist who ensures that existing thermal bridges are eliminated.

When replacing windows, care must be taken to ensure that the walls are properly insulated. If the energy quality of the window is higher than that of the walls, condensation can accumulate on the walls and cause mould growth. Condensation always settles in the coldest places.

In order to be eligible for state subsidies, it is essential that walls are well insulated. When replacing windows, it may therefore be necessary to also insulate the facade. Contact your Klima-Agence advisor to determine the insulation performance of your building.

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Window replacements should always be followed up with adequate daily airing to maintain a healthy room climate.

A properly implemented energy renovation improves the energy efficiency of the building and helps reduce dependence on rising energy prices because it decreases heating energy consumption. To maintain or increase the value of a building, it is essential to take a long-term view of its maintenance and modernisation. While some renovated elements may take up to ten or twenty years to recoup their value, others pay off very quickly. To find out more about the potential for improving the energy efficiency of your home, ask for a free energy check with a Klima-Agence advisor. 

Various state and municipal grants are also available to help you finance your energy renovation project.

Thermal insulation is one of the most important measures for improving the energy efficiency of buildings. It enables higher savings in heating energy expenses than any other measure.

The production of insulation materials consumes significantly less energy than is subsequently saved. The energy required for the production of insulation materials is minimal compared to the amount of heating energy saved over 20 to 30 years. The energy expended in the production of insulation material is therefore not an argument against energy-efficient renovation. It is, however, important to choose a suitable insulation materials. Ecological insulation materials that meet the criteria for state subsidies are produced in an energy-saving way.

In the context of the state subsidy programme, a substantial increase in grants is allocated for the use of ecological insulation materials.

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An insulating material is not the cause of a fire. Insulation materials are categorised according to different fire protection classes, depending on their degree of flammability. A European norm regulates the classification of building materials and building types according to their fire behaviour.

Insulating materials made of mineral materials are essentially non-combustible. They fall under Luxembourg’s sustainability certification for residential buildings (LENOZ) and can therefore be subsidised by the state as part of an overall renovation concept. This also applies to the renovation measures themselves: choosing mineral-based insulation materials results in higher financial support than conventional materials.

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Certain materials used for facade cladding can be combustible. That is why it is important to consider the overall composition of the exterior wall. However, walls may also contain certain fire protection elements (coating, fire bars, etc.) that prevent flames from spreading.

Homes constructed between 1900 and 1970 possess great potential for energy renovations. In order to find out the energy performance of an insulation, each property must be assessed individually. Klima-Agence offers free energy checks to analyse the situation of your home's insulation.

The opposite is true: wall joints cause significant heat loss. In winter, warm, moist air escapes through unsealed areas such as joints and cracks. As a result, the air cools down and moisture settles as condensation, which can lead to mould growth in hollow spaces. Thermography can be used to identify areas where heat loss occurs.

An energy renovation (facade insulation, roof insulation, replacement of windows) makes the building more airtight and thus improves its energy efficiency.

The outer plaster layer on insulated walls has a lower temperature, which causes rainwater and condensation to dry more slowly. However, various factors have to be taken into account when it comes to the development of microorganisms: weather conditions, orientation, proximity to trees or bushes and lack of protection provided by overhanging parts of the building. It is hence important to consider certain adaptations to reduce the risk of algae infestation already in the planning phase. Roof overhangs and window sills as well as plinth areas protect facades from precipitation and splash water. This prevents moisture from penetrating the surface of the building and limits the spread of fungi or algae.

It is likewise important to choose suitable building materials. High density insulation materials such as wood fibres, cellulose or hemp fibres store heat better. The facade cools down more slowly and less condensation forms on the surface of the plaster. The risk of fungus or algae growth is reduced. 

Walls do not “breathe” as such. Air exchange and moisture removal is only possible through ventilation (by opening windows regularly or installing a ventilation system). What is commonly referred to as "breathing" is the transport of moisture by water vapour diffusion. In practice, breathing only plays a negligible role in the removal of moisture. By contrast, it is important that the interior plaster can absorb moisture from the air and release it back into the room after ventilation. The moisture-regulating effect is therefore only achieved on the first few centimetres (on the inside) of a wall. Clay plaster on interior walls, for example, regulates humidity particularly well.