FAQ

In all cases, a properly executed energy retrofit improves the energy efficiency of the building and helps to reduce dependence on higher energy prices by reducing energy consumption for heating. In order to guarantee the sustainability of a dwelling and to maintain/increase its value, its maintenance and modernisation need to be considered in view of the long term. Whereas some retrofitted elements might depreciate in 10 or 20 years, for other elements this can happen much faster. To learn more about the potential for improving the energy efficiency of your home, request a free energy assessment with a Klima-Agence adviser.

Various State and municipal aid is also available to help finance your energy retrofitting project.

When replacing windows, one should take care to ensure that the walls are properly insulated. If the energy quality of the window is higher than that of the wall, humidity can condense on the walls, thus giving rise to the formation of mould. Condensation always appears in the coldest places.

To benefit from Klimabonus support, the performance of the wall insulation must be higher than that of the new window, or the windows must be replaced and controlled mechanical ventilation installed. When replacing windows, it may therefore also be necessary to insulate the façade. Contact your Klima-Agence adviser to determine the insulation performance of your building (free energy assessment).

In any case, after your windows have been replaced, proper daily ventilation must be ensured to maintain a healthy climate in your home.
 

When windows are not properly sealed, it leads to insufficient and unreliable ventilation and generally prevents correct ventilation in a dwelling. Adequate ventilation is achieved by opening windows or using a comfort ventilation system (CMV). On the other hand, windows that are not tightly sealed cause heat loss and draughts on cold days. These factors thus combine to create an unpleasant indoor climate and unnecessarily high heating costs.  

In you are retrofitting, it is advisable to have the new windows installed by a specialist, who will take care to remove any existing thermal bridges.

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.  
 

Regular maintenance of a rendered façade can considerably reduce the risk of algal growth and fungal attack. Façades most at risk (north-facing and shaded façades) must be cleaned regularly by a specialist company and painted if necessary. Damaged connection and expansion joints on window sills and air outlets of ventilation systems should be renewed.

In the case of composite thermal insulation systems, the choice of material and the application of the coating can delay the formation of algae. The following materials should be preferred:

• mineral renders;
• thick renders;
• renders without the addition of colour, which require a coat of paint after application;
• smooth-textured finishing renders.

Many renders contain biocides (pesticides) that are supposed to prevent the growth of algae and fungi, but over time these biocides are washed off by rain and end up in waterways and soils. Mineral renders are an environmentally friendly alternative to renders containing biocides.

Heavy insulating materials (with high bulk density) store heat better than light insulating materials. During short periods of low temperature, the façade cools down more slowly and less condensation forms on the rendered surface, which reduces the risk of algal and fungal growth.

Heavy insulating materials are generally made of renewable raw materials: wood fibres, cellulose, hemp, etc. The Luxembourg aid scheme Klimabonus provides for a specific category for insulation materials made from renewable, environmentally friendly raw materials with a higher subsidy.

In general, ventilated curtain walls and monolithic structures without a composite thermal insulation system are less vulnerable to algal and fungal growth.

Eaves and window sills as well as the substructural areas protect façades from rain and water splashes and thus reduce the risk of algal and fungal growth. This constructive protection against moisture is part of the architectural design and must be taken into account in the design phase.