Energy renovation: improve your home

Replacing a boiler or installing a heat pump before addressing insulation often means oversizing the new equipment to compensate for the heat losses of a poorly insulated building. An envelope that loses heat through the roof, walls or windows requires a more powerful, and therefore more expensive, heating system, while an envelope treated beforehand allows a smaller, better-matched appliance to be chosen.

The logical order is therefore to first reduce the building's heat demand, then size the heating equipment to that reduced demand. This logic also shapes public support schemes, which favour a coherent approach over a series of works decided independently of one another.

A typical renovation path starts with an energy audit and the drawing up or updating of the dwelling's energy passport, which objectively identifies weak points before any expense is committed. Next comes the roof and attic, where heat losses are usually largest and the ratio between cost and gain is generally the most favourable.

Wall insulation, whether external or internal depending on the building, logically follows, ahead of window replacement and airtightness work, which must be coordinated to avoid thermal bridges at the junctions. Ventilation comes next, essential as soon as the building becomes tighter, and only at the end come heating and technical installations, now sized to a genuinely reduced demand.

This sequence is not rigid: the building's configuration, an unexpected repair or a work opportunity can change the order, but the underlying principle remains — treat the envelope before choosing the final equipment.

The dwelling's energy passport rates the building according to its thermal performance and identifies the areas responsible for heat losses. It serves as a basis for prioritising works, but also as a common, factual reference when discussing a project with companies and advisory bodies rather than relying on impressions.

It is recalculated after significant works, which makes it possible to objectively measure the progress achieved and check that successive interventions have genuinely improved the targeted energy class.

Few households carry out all the works at once. A renovation spread over several years remains effective provided it is planned from the outset according to the order described above, so that a step treated too early does not have to be redone because of a later step: insulating walls before deciding on the window type, for instance, can force a rework of the junctions.

A written multi-year plan, even a simple one, makes it possible to schedule subsidy applications, anticipate quotes and book companies in a sensible order, rather than deciding step by step based on commercial opportunities as they arise.

The Klimabonus Wunnen, which replaced the former PRIMe House programme in 2022, covers several strands of energy renovation: insulation, windows, ventilation, heating and renewable electricity generation. A coordinated approach makes it possible to combine these strands within a single project rather than treating them separately, which simplifies the application process and avoids redundant administrative steps.

The amounts and conditions applicable to each strand are published on the official guichet.lu website and change over time; they should not be copied from a commercial source. Klima-Agence offers free, independent energy advice, particularly useful for sequencing a project that combines several types of works and several subsidy applications.

A complete energy renovation involves several trades: roofers and carpenters for the roof, façade specialists for external insulation, joiners for the windows, heating engineers and electricians for the technical installations, and often a dedicated ventilation company. Their work must be carefully sequenced: airtightness work, for example, is done before interior finishes are installed, and mechanical ventilation should be installed before or at the same time as the last insulation works to avoid any moisture problem in the meantime.

Insulating a building without reviewing its ventilation increases the risk of condensation and mould, because the humid air produced by occupants can no longer escape through the gaps that previously existed in the envelope. Treating ventilation in the same sequence as insulation, not as an afterthought, is therefore a condition for the project's success, not a comfort option.

For a project spanning several types of works, it is worth checking that each company holds the establishment authorisation matching its trade and carries professional liability insurance. Ask for detailed quotes broken down by trade, based on the same assumptions for surface area and materials, so they can be compared properly.

Vert.lu puts homeowners in touch with companies from its directory that match the trade and area sought; you describe your project, available companies contact you, and you remain free to compare and decide without obligation.