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.  
 

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.

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.

The values of the I_eco12 indicator are provided for some commonly used insulation materials in Chapter 7.3 of the Annex to the Grand Ducal Regulation on the Certification of the Sustainability of Housing and can be reused.

In the event that other insulation materials are used, experts can calculate the I_eco12 indicator using the I_calc calculator, which can be viewed online 

The I_eco12 indicator is used to assess new insulation installed on an existing building and is taken into consideration in the following cases:

• in the case of sustainable energy retrofitting of elements of the thermal building envelope under the Klimabonus subsidy scheme;
• as part of the LENOZ certification of an existing retrofitted building.

In the context of the building permit application procedure, it is necessary to respect the municipal planning regulations relating to setbacks from neighbouring private properties. The same provisions apply to constructions along the municipal public domain.

With regard to building permits, the municipalities systematically check that buildings are set back from the municipal public domain or plot boundaries.

As a rule, the planning regulations for setbacks are regulated by the municipalities in their General Development Plan (Plan d’Aménagement Général, PAG) or in the Special Development Plans (Plans d’Aménagement Particulier, PAP).

For municipalities whose PAG has not yet been adapted to include current legislation, the planning regulations relating to setbacks are still included in the written part of the PAG or in the building regulations. For these municipalities, the measurement of setbacks in the event of energy retrofitting is set out individually, by municipality, in those documents.

On the other hand, for those municipalities whose PAGs have been completely revised since 2011, the Grand Ducal Regulation that is the basis for the applicable definitions provides that the building setbacks are to be measured without the additional insulating layer in the case of an energy retrofit.

In both cases, the municipalities can include derogation mechanisms in their regulations in order to promote energy retrofitting, for example through a reduction in the minimum setback to be observed.

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.