FAQ

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.  
 

Calculation of the environmental indicators is directly linked to calculation of the thermal transmittance U and its inherent calculation rules. However, the layers of membranes and seals, which are negligible when calculating the thermal transmission coefficient given their low impact in terms of their insulation capacity, should be taken into consideration for calculation of the predicted environmental indicators.

For a new building, the construction elements of the thermal envelope (= external structure) as well as internal walls and slabs are taken into account.

For the elements of the external structure, all the layers taken into consideration for calculation of the U value are also taken into consideration for calculation of the I _env and I_prim indicators.

Party walls and partition walls between different units in a block of flats should be considered internal walls (within the building envelope).

For existing buildings, only new insulating materials used during the retrofitting works are taken into consideration.

For existing buildings, only the primary energy requirement of the technical installations for conditioning the building should be considered for the I_prim indicator (Chapter 4.2). The primary energy expenditure of the existing building is not taken into account. 

In general, the environmental indicators I_env and I_prim are calculated automatically (from the database implemented in the Lux-Eeb-H software) when filling in the calculation sheet for the thermal transmission coefficients of the different layers making up the thermal envelope (U value).

Section 7.3 of the Annex to the Grand Ducal Regulation on housing sustainability certification uses the I_env indicator for different constructions. Current data on building materials, recorded in the LuxEeB-H software, can be viewed in the Materialdaten LENOZ 2016 document on the website http://www.ml.public.lu/fr/lenoz/Experts/index.html.  

A LENOZ certificate can be issued for all residential buildings with an energy passport, whether they are new or existing residential buildings. Issuance of the certificate is associated with Class 4 "minimum sustainability" (Chapter 0.2 of the Annex to the Grand Ducal Regulation on housing sustainability certification). Existing residential buildings can achieve this "minimum sustainability" by means of comprehensive retrofitting works.

In general, all costs relating to the works necessary for the installation of insulation are considered eligible costs. A detailed list of the works considered is available from the Environmental Administration.