FAQ

Mould growth is associated with elevated humidity levels and insufficient ventilation rather than with good insulation practice.

Indeed, the reverse is true: improved insulation quality prevents the formation of mould. This is found to be the case in many energy-efficient homes and buildings that have been retrofitted for energy efficiency. They are perfectly insulated, airtight and completely free of mould. If the external walls are not satisfactorily insulated, air moisture condenses in the cold areas, which favours the formation of mould. Effective thermal insulation of the façade tends to raise the surface temperature of the external wall and thus prevent moisture from accumulating.

It is likewise important to identify and eliminate all thermal bridges in the building (i.e. places where there are gaps in the insulation). Such bridges can be found, among other places, in recesses for radiators or on balconies. In addition, it is not advisable to place furniture in front of external walls, as this prevents the indoor air from circulating freely, meaning that the surfaces behind the furniture cool down.  
 

In principle, a wall does not breathe. Air renewal and moisture removal are only achieved by ventilation (via windows or a mechanical ventilation system). The effect of 'breathing' as mentioned above refers to the transfer of moisture by the diffusion of water vapour. In practice, this is minimal and does not play any role in the removal of moisture. On the other hand, it is important for interior plaster to be able to absorb moisture from the air and release it back into the interior after ventilation. The moisture regulation effect therefore only operates within the first few centimetres (on the interior side) of a wall. For example, clay plaster on internal walls provides excellent moisture regulation.

It is often façade insulation systems that are implicated and pilloried for this. It is true that on insulated walls the outer render layer has a lower temperature and slows down the drying of rainwater and condensed water. However, in order to determine the origin of the spread of micro-organisms, various factors have to be taken into consideration: weathering, orientation, proximity of trees or bushes and the lack of protection provided by protruding building elements (roof overhang, window sill, projection, eaves, etc.).

For new builds, weather protection should ideally be provided from the outset. Similarly, by opting for a thicker finishing coat, higher surface temperatures can be obtained.

On the contrary! Poor quality sealing can result in significant amounts of energy loss. However, the risk of building deterioration is an even greater factor: in winter, warm, moist air escapes to the outside through leaky areas such as joints and cracks. In this way, the air cools down and moisture condenses, which can lead to the formation of mould in the cavities. In most cases, we don't even notice it and therefore we can't react.

Airtightness is therefore a key issue. You must ensure that your house is well ventilated, either simply by opening the windows or by installing a controlled ventilation system.

Insulating materials are not all flammable. Building materials, and therefore also insulating materials, are divided into different fire protection categories. Moreover, a European standard regulates the classification of products and types of construction according to their fire behaviour.

This standard indicates that there are non-flammable insulating materials. Therefore, the main contractor can inquire about this beforehand, prior to deciding on the materials to be used. In principle, insulating materials made out of minerals are non-flammable. Mineral-based insulation materials are also covered by the Luxembourg Sustainability Certification for Housing (LENOZ) and can therefore be financed by the State as part of an overall project. Refits are also covered: the use of mineral-based insulation materials allows for higher financing than conventional materials.

Furthermore, there are other materials used as façade cladding elements that are flammable and these must be taken into account in this regard. This is why it is important to account for the overall make-up of the external wall in itself. Nonetheless, it may also include flame retardants (i.e. sealant, firewall, etc.) and thus provide protection against the spread of flames.

When improving building energy efficiency, insulation measures have the highest priority. No other measure can save as much energy for heating.

Several studies demonstrate that the production of insulation materials consumes much less energy than is saved later. Even with 30-centimetre thick insulation materials, such as polystyrene, the production energy required is already amortised after about three years.

Houses are used for decades; in terms of their maintenance and modernisation, one must therefore take a long-term view. Every owner who adopts a sustainable approach will invest in the building to maintain or increase its value. Some measures pay for themselves very quickly, others only after 10 or 20 years. In all cases, a properly executed energy retrofit contributes to reducing dependence on rising energy prices by reducing energy consumption for heating. And even if, in rented buildings, the savings in heating energy do not immediately compensate for any increase in rent, one must always take into consideration the fact that heating energy prices are constantly rising. In most cases, therefore, the measures pay off in the long term.

When calculating the cost of an energy modernisation, don't forget that many measures will have to be implemented sooner or later and that financial aid can be requested today.

If you rely on non-airtight windows to ensure good ventilation, you are sure to make a mistake and it will be an expensive error: the exchange of air takes place in a purely random way, depending on the weather conditions and air pressure. On the other hand, on the coldest days you can be sure that you will suffer from heat loss. In addition, there is a risk that moisture in the air will condense on single-glazed windows, leading to the formation of mould. Windows that are not airtight will lead to an unpleasant indoor climate and unnecessarily high heating costs.

In the case of retrofitting, new windows must be installed by a specialist who not only works with the latest materials but also ensures that existing thermal bridges are eliminated.

Mould growth is caused by poor construction standards or poor/insufficient ventilation, not by levels of insulation.

In fact, if you insulate your house properly, you will prevent mould growth. This can be seen in many passive houses and in buildings undergoing energy retrofitting. These buildings are well insulated, airtight and completely free of mould. If the external walls are not satisfactorily insulated or not insulated at all, air moisture condenses in the cold areas, thus giving rise to the development of mould. Thermal insulation of the façade tends to raise the surface temperature of the external wall and prevent moisture from accumulating.

In this context, it is important to identify and eliminate all thermal bridges in the building. These include, for example, window apertures, i.e. the wall surfaces facing into the window or door openings, against which the respective frames are placed. In addition, external walls should not be encumbered with furniture, as this prevents the indoor air from circulating, meaning that the surfaces behind any furniture cool down.

Therefore, in summary, proper insulation of the façade and adequate ventilation are key measures that prevent mould growth.