Roof and attic insulation in Luxembourg 2026: methods, costs and Klimabonus grants
By Yacine Sahnoune, founder of renov.lu
The roof accounts for 25–30% of the heat lost from a Luxembourg home — it is the first insulation job to tackle, even before the walls. In 2026, insulating your attic or roof can save you up to €800 a year on heating bills, while qualifying for the overhauled Klimabonus Wunnen (up to €115/m² for eco-friendly insulation on the roof, or €140/m² if the approval in principle is requested before 30 June 2027) and for Enoprimes, which can be claimed on top. Depending on your attic — unconverted (loft), convertible or converted — the method and the budget vary considerably. This complete guide gives you everything you need to choose the right solution, maximise your grants and avoid the most expensive mistakes.
- Unconverted attic (loft): blown-in insulation costs €35–70/m² installed in Luxembourg, i.e. €2,800–5,600 for 80 m², done in a single day.
- Sloping roof and sarking: allow €90–160/m² to insulate a sloping roof with wood fibre (between and under the rafters) and €180–350/m² for sarking with a new roof covering.
- Klimabonus 2026: on the roof, €60–85/m² for mineral insulation and €90–115/m² for eco-friendly insulation; on the floor of an unconverted attic, €40–65/m² for eco-friendly insulation.
- Increase and cap: the amounts are higher if the approval in principle is requested before 30 June 2027 (€140/m² instead of €115/m² for eco-friendly roof insulation at standard I); the grant never exceeds 60% of the cost of the work excluding VAT.
- 3% VAT: roof insulation on a main residence that is at least 10 years old is invoiced at 3% instead of 17% VAT.
- Conditions: at least 20 cm of CE-certified insulation (λ = 0.035, standard III) and an approval in principle obtained on MyGuichet.lu before work starts.
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Why insulate the roof first in Luxembourg?
In Luxembourg’s housing stock, the roof is invariably the first thermal weak spot to deal with. Heat naturally rises to the upper parts of a home and escapes through an uninsulated roof — that is simple building physics. In summer, the process is reversed: an uninsulated roof lets the sun’s heat in and the upstairs rooms overheat. If you are unsure about your priorities, our guide to energy renovation in Luxembourg ranks the works in order, and our Klimabonus application steps cover the formalities. In summer, heat also comes in through the roof; a recent idea: the cool roof coating made from oyster shells.
| Part of the building | Share of heat loss | Priority |
|---|---|---|
| Roof / attic | 25–30% | Priority 1 |
| External walls | 20–25% | Priority 2 |
| Windows and glazing | 10–15% | Priority 3 |
| Ground floor / basement | 7–10% | Priority 4 |
| Thermal bridges and air leaks | 5–10% | Supplementary |
Insulating your roof or attic in Luxembourg can cut heating consumption by 25–30%, an estimated annual saving of €500–800 for a single-family house heated with oil or gas. It is also the most technically straightforward job — especially for unconverted attics, where blown-in insulation can be completed in a single day, with no major building work and no need to move out temporarily.
If you are also considering a heat pump, insulate the roof and attic first. A better building envelope reduces the heating output you need, so you can opt for a smaller — and therefore cheaper — heat pump while maximising its COP. Roof insulation is the prerequisite for any optimisation of your heating system. It also directly improves your energy class on the energy performance certificate (CPE).
Would you like quotes from verified contractors to insulate your roof in Luxembourg? Free, no obligation.
Request quotes →What type of attic do you have? The initial assessment
First and foremost, you need to identify your attic configuration, because it entirely determines which insulation method can be used. There are three main situations, each calling for a different strategy.
Unconverted attic (loft)
The space under the roof is neither habitable nor converted. It serves only as a service void. This is the most common configuration in Luxembourg houses built between the 1960s and the 1990s. Recommended solution: blown-in loose-fill insulation on the attic floor. The quickest and cheapest method.
Converted or convertible attic
The space under the roof is lived in or is intended to be. The sloping sections of the roof (the inside of the roof pitches) form the walls of the rooms. Recommended solution: insulation under the sloping roof (from inside) or sarking (over-rafter insulation from outside, when the roof covering is being replaced). A more complex and more expensive job.
If you are planning to convert your unconverted attic within the next 5 to 10 years, do not insulate at floor level now. Go straight for sloping-roof insulation or sarking — you will avoid having to redo everything later and paying twice. Discuss your long-term plans with your contractor before making any decision. If you are considering attic conversion work, now is the right time to coordinate the two projects.
An energy assessment carried out by an approved energy advisor gives you an objective picture of the situation and helps you prioritise the work. For single-element projects (a single insulation measure), this assessment is not compulsory under the Klimabonus 2026 — a simplified procedure applies.
Loft insulation (unconverted attics) — blown-in and floor insulation
Insulating an unconverted attic is the most cost-effective and quickest method to carry out. The principle is simple: a thick layer of insulation is laid directly on the attic floor, between and over the existing joists. The aim is to create a thick thermal barrier at the level of the floor that forms the ceiling of the storey below, without touching the roof covering or the roof structure.
Blown-in insulation
The most effective method for unconverted attics is blown-in loose-fill insulation: the contractor uses a blowing machine to spread the insulation (cellulose, rock wool or glass wool flakes) evenly over the whole surface, including hard-to-reach areas. The technique ensures a uniform layer with no thermal bridges, even in corners and around obstacles (chimneys, mechanical ventilation units, electrical boxes).
Marking out protected areas
Before blowing, the contractor locates and protects electrical boxes and ventilation inlets, and keeps a fire-safety clearance around any flue or recessed light fitting. Graduated depth markers are fixed to the joists to check the blown thickness and ensure an even layer.
Fitting a vapour control layer if necessary
In attics at risk of condensation (poorly ventilated old floors, damp areas), a vapour control membrane is laid under the insulation to stop moisture migrating towards the roof timbers. It is essential with certain concrete floor configurations and in Luxembourg houses built before 1970.
Blowing the insulation to the target thickness
For the Klimabonus, the minimum thickness is 20 cm for insulation with λ = 0.035 W/(m·K) (standard III); standards II and I, which attract higher grants, require a U-value of no more than 0.13 and 0.10 W/(m²·K) respectively for the attic floor. To achieve the best performance — and the higher Klimabonus grants — it is advisable to aim for 30–40 cm, depending on the material. Cellulose and wood fibre are the most recommended insulation materials for this configuration, both for their thermal performance and for the eco-friendly Klimabonus rate.
Access hatch and walkways
If access to the attic needs to remain usable, the contractor fits an insulated box around the hatch and, if people will need to move around the attic, walkways (crawl boards) to protect the insulation and provide access to equipment.
For an unconverted attic of 80–120 m², a blown-in insulation job is completed in a single day. You do not need to leave your home or move any furniture. It is by far the least invasive insulation method, with one of the fastest paybacks of any energy renovation project.
Insulation with rolls or boards (laid by hand)
For accessible unconverted attics with a regular layout, laying rolls or boards of insulation (mineral wool, hemp, wood fibre) is an alternative to blowing. A first layer is laid between the joists, then a second layer crosswise on top, to avoid any thermal bridging at the joists. This method takes slightly longer but qualifies for the same Klimabonus grants.
To qualify for Klimabonus roof insulation grants, the insulation must be CE-certified and laid to a minimum thickness of 20 cm for a λ of 0.035 W/(m·K) (standard III); standards II and I require a U-value of no more than 0.13 and 0.11 W/(m²·K) respectively for the roof. If the attic is heated, the roof renovation must also include replacing roof windows more than 10 years old with a Uw above 1.4 W/(m²·K). Non-recycled fossil-based insulation (conventional PUR polyurethane, standard expanded polystyrene) is no longer subsidised. Ask your contractor for the certified CE technical data sheet before approving the material — a missing data sheet can lead to your Klimabonus application being rejected.
Convertible attic insulation — insulating under the sloping roof
When the attic is converted or is intended to be, you need to insulate the sloping roof — the pitched sections of the roof that form the walls of the rooms under the roof. Insulation from inside (under the sloping roof) is the standard method in this case; it preserves the appearance of the roof covering and does not require access to the roof.
Insulation between and under the rafters
The classic method is to fit insulation boards (wood fibre, rock wool, hemp) between the rafters of the roof structure, then add a crosswise layer screwed under the rafters. This double layer eliminates the thermal bridges created by the timber of the rafters themselves (which conduct heat and cause significant linear heat ‘leaks’). A vapour barrier or humidity-variable vapour control layer is then fitted on the inside, before the final finish (plasterboard, timber panelling).
Insulation between the rafters only
Advantages: cheaper, quicker to install, no loss of ceiling height.
Drawbacks: residual thermal bridges at the rafters (around 15–20% of the total surface area). Actual performance is lower than the theoretical value of the insulation. Less suitable for reaching the higher Klimabonus thresholds.
Insulation between + under the rafters (double layer)
Advantages: no thermal bridges, optimal performance, access to the higher Klimabonus grants, better summer comfort with materials that offer a long thermal phase shift.
Drawbacks: higher cost, slight loss of ceiling height (5–8 cm), longer job.
To reach the U-values for standards II and I (no more than 0.13 and 0.11 W/(m²K) for the roof) and qualify for the highest Klimabonus grants, always opt for the double layer (between + under the rafters). Losing a few centimetres of height is more than offset by the energy savings and the grants you receive. Wood fibre boards are ideal for this configuration: they provide excellent summer insulation thanks to their long thermal phase shift (~10 hours), which is particularly valuable for homes in Luxembourg’s valleys that overheat in summer.
Blowing insulation between the rafters (attics already finished)
In converted attics that are already finished (plasterboard in place), loose-fill insulation (cellulose, mineral wool) can be blown into the existing space between the rafters and the interior lining, without taking down the ceilings. The contractor drills small holes in the lining, blows in the insulation and fills the holes. This technique is worth considering for light renovations, but it does not guarantee full coverage or sufficient thickness unless the available space is checked beforehand.
Sarking — insulating a pitched roof from outside
Sarking is the highest-performing method of insulating a pitched roof. It involves fitting rigid insulation boards over the roof structure, between the rafters and the roof covering. The result: a continuous insulating envelope with no thermal bridges at all, which also protects the roof timbers from extreme temperature swings and extends their lifespan.
When should you choose sarking?
When the roof covering is being completely replaced
Sarking means completely removing the existing roof covering (tiles, slates). If you need to redo your roof anyway — covering at the end of its life, recurring leaks, a house from the 1960s–1980s — take the opportunity to add sarking. The marginal extra cost of the insulation is then very small compared with the total cost of the roofing work.
To preserve the living space in your attic
Unlike insulation under the sloping roof, sarking does not eat into the interior space. It is ideal if your converted attic already has limited ceiling heights, or if you want to keep the exposed roof timbers as a decorative feature.
For maximum performance with no thermal bridges
Sarking eliminates all thermal bridges — including those caused by the rafters, braces and trusses of the roof structure. It is the only method that guarantees perfectly continuous insulation over the whole roof slope, which is essential for reaching the passive house standard.
The stages of a sarking project
The roofer starts by completely removing the existing roof covering until the roof structure is exposed. They inspect the condition of the timbers and carry out any necessary repairs (insecticide treatment, replacement of damaged members). The rigid insulation boards — wood fibre, polyisocyanurate (PIR) or rock wool boards — are then fixed directly to the rafters or to timber boarding. A high-performance roofing underlay (breathable membrane) is rolled out and stapled over the insulation. Counter-battens create a ventilated air gap, then the battens and the new roof covering are laid on top.
In Luxembourg, any change to the appearance or volume of a roof may require a municipal building permit. Sarking raises the height of the roof slightly (by a few centimetres, depending on the thickness of the boards). Check with your municipal administration (commune) before starting work — especially if you live in a protected site or a historic town centre. A PAP (Plan d’Aménagement Particulier, a detailed local development plan) may impose restrictions on roofing materials.
Since 2026, Luxembourg’s Klimabonus has included a grant for green roofs. If you carry out sarking and add a green roof (substrate ≥ 10 cm), you can combine the insulation grant with the green roof grant. Check the exact conditions with the Klima-Agence.
Flat roof insulation in Luxembourg
Flat (or very low-pitched) roofs are common in Luxembourg buildings from the 1970s to the 2000s and in modern extensions. Insulating them follows a different logic from pitched roofs. A flat roof in poor condition can combine roof waterproofing and insulation work in a single project, which is generally the most economical solution.
Warm roof (insulation above the structure)
The insulation is laid above the vapour barrier and under the waterproofing membrane. The roof structure or concrete slab stays at room temperature. This is the highest-performing method for flat roofs: no risk of condensation within the structure, and the longest possible lifespan for the waterproofing membrane. It is recommended by the Klima-Agence and qualifies for the Klimabonus.
Inverted roof (insulation above the waterproofing)
The insulation (high-density extruded polystyrene, XPS, which is water-resistant) is laid over the existing waterproofing membrane, then weighted down with gravel or paving slabs. Advantage: no demolition needed, ideal for renovation. Drawback: XPS insulation is no longer subsidised by the Klimabonus unless it contains more than 50% recycled material. Check that the product complies before committing to the work.
For flat roofs in poor condition that need new waterproofing, a warm roof with rigid insulation boards (PIR polyisocyanurate, high-density rock wool) is the preferred solution. It is carried out at the same time as the new waterproofing, for an optimised overall cost and a single call-out for the contractors.
Roof and attic insulation materials compared in 2026
Choosing the insulation is a strategic decision: it determines thermal performance, summer comfort, eligibility for Klimabonus grants and the overall budget. Here is a full comparison of the materials suitable for roof and attic insulation in Luxembourg. For an even more detailed comparison covering every application, see our page insulation materials compared in Luxembourg.
| Material | λ (W/m·K) | Thermal phase shift | Klimabonus 2026 | Main use | Key points |
|---|---|---|---|---|---|
| Wood fibre | 0.038–0.042 | 10–12 h (excellent) | €90–115/m² on roofs (+€15/m² if certified) | Sloping roofs, sarking, unconverted attics | Best summer comfort, bio-based, 60-year lifespan |
| Cellulose | 0.038–0.043 | 8–10 h (very good) | €40–65/m² in unconverted attics, €90–115/m² on sloping roofs | Unconverted attics (blown-in), sloping roofs (blown into cavities) | Ideal for blowing, recycled (paper), competitively priced |
| Hemp wool | 0.038–0.045 | 7–9 h (good) | Eco grant if certified bio-based | Unconverted attics, sloping roofs | 100% natural, regulates humidity, low carbon footprint |
| Rock wool | 0.033–0.040 | 4–5 h (average) | Standard grant | Sloping roofs, unconverted attics, sarking | Excellent fire barrier, moisture-resistant, affordable |
| Glass wool | 0.030–0.040 | 3–4 h (low) | Standard grant | Unconverted attics (rolls, blown-in) | Most widely used insulation, low price, lightweight, good thermal performance |
| PIR / Polyisocyanurate | 0.022–0.028 | 2–3 h (low) | Not subsidised (fossil-based) | Sarking, flat roofs | Best performance per cm, compact, but fossil-based and not eco-friendly |
| Spray polyurethane foam (PUR) | 0.022–0.028 | 2–3 h (low) | Not subsidised (fossil-based) | Specific hard-to-reach situations | Airtight, bonds to the substrate, but not recyclable — excluded from the Klimabonus unless >50% recycled |
Sources: Klima-Agence Luxembourg — Klimabonus Wunnen 2026. λ values: CE certifications (ACERMI). Thermal phase shift: manufacturers’ data, EN ISO 13786 standard.
To maximise year-round thermal performance, summer comfort and Klimabonus grants all at once, wood fibre (boards for sloping roofs and sarking) and cellulose (loose-fill for unconverted attics) are the two materials to favour. They qualify for the highest eco-friendly Klimabonus grants and offer a level of protection from summer heat that conventional mineral insulation cannot match. Luxembourg’s rules clearly favour these bio-based materials.
Roof and attic insulation cost in Luxembourg in 2026
Prices in Luxembourg are higher than French or Belgian averages, because of labour costs and the margins on the local market. Below are the price ranges we have gathered from verified partner contractors. For an overview of all insulation work, see our page insulation costs in Luxembourg.
| Type of work | Method / material | Average price in Luxembourg (supply + installation) | Budget for 80 m² |
|---|---|---|---|
| Unconverted attic | Blown-in glass / rock wool | €35–60/m² | €2,800–4,800 |
| Unconverted attic | Blown-in cellulose | €45–70/m² | €3,600–5,600 |
| Unconverted attic | Mineral wool rolls / boards laid by hand | €40–75/m² | €3,200–6,000 |
| Converted attic — sloping roof | Wood fibre boards (between + under the rafters) | €90–160/m² | €7,200–12,800 |
| Converted attic — sloping roof | Rock / glass wool boards (between + under the rafters) | €80–140/m² | €6,400–11,200 |
| Sarking — external insulation | Wood fibre boards + new roof covering | €240–350/m² | €19,200–28,000 |
| Sarking — external insulation | PIR / high-density rock wool boards + new roof covering | €180–280/m² | €14,400–22,400 |
| Flat roof — warm roof insulation | PIR or high-density rock wool + waterproofing | €150–280/m² | €12,000–22,400 |
Indicative prices including VAT (3% VAT for homes at least 10 years old), compiled by Renov.lu from verified contractors — Luxembourg, 2026. Prices vary depending on the municipality, access and the complexity of the job.
Factors that affect the price
Attic access
Attics that are hard to get into (narrow hatch, unstable floor, low headroom under the ridge) add 10–20% to labour costs. Attics with a concrete floor are easier to work in than those with an old, non-load-bearing timber floor.
Roof area and shape
Roofs with multiple pitches, valleys, dormers, roof windows and changes in level make the job considerably longer. A simple roof with two regular pitches costs significantly less per m² than a complex roof.
Condition of the roof structure and existing insulation
If there is old insulation that has deteriorated or is damp, it often has to be removed before the new insulation is blown in. This extra work is charged at €5–15/m², depending on the volume involved.
Roof covering material for sarking
A new slate roof (€80–150/m²) costs considerably more than concrete tiles (€30–60/m²) or clay tiles (€45–90/m²). This choice can double the total cost of sarking.
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Get my quotes →Klimabonus and Enoprimes grants for roof insulation in 2026
The Klimabonus Wunnen, completely overhauled from 1 January 2026, now pays flat rates in €/m² for insulation, unlike the previous scheme, which was calculated as a percentage of the cost. For roofs and attics, the amounts vary according to the type of insulation and whether it is eco-friendly. For an overview of all the grants available, see our page Klimabonus grants and subsidies in Luxembourg.
Klimabonus amounts 2026 — roof and attic insulation
| Type of insulation | Basic Klimabonus (€/m²) | Certified eco insulation bonus | Bonus for >50% recycled materials | Maximum combined total |
|---|---|---|---|---|
| Mineral insulation (glass wool, rock wool) — roof | €60–85/m² | — | +€15/m² | €100/m² |
| Eco-friendly insulation (wood fibre, hemp, cellulose…) — roof | €90–115/m² | +€15/m² (certified sources: FSC, PEFC, natureplus…) | — | €130/m² |
| Eco-friendly insulation — unconverted attic floor (loft floor slab) | €40–65/m² | +€15/m² | — | €80/m² |
Source: Guichet.lu and Klima-Agence Luxembourg — Klimabonus Wunnen scheme in force since 1 January 2026. Basic amounts (standards III to I), increased if the approval in principle is requested before 30 June 2027 (for example €140/m² instead of €115/m² for eco-friendly insulation at standard I); the grant is capped at 60% of costs excluding VAT — check the exact figures on myguichet.lu.
Grants you can combine with the Klimabonus
| Source of funding | Amount | Key conditions |
|---|---|---|
| Klimabonus Wunnen | €20–115/m² depending on the element (attic floor slab or roof), the insulation and the standard; €25–140/m² if the approval in principle is requested before 30 June 2027 | thickness ≥ 20 cm (λ = 0.035), approved company or support from an energy advisor, approval in principle before work starts |
| Enoprimes (Enovos and Sudenergie) | Depends on the measure (e.g. €12/m² for roof insulation) | File opened BEFORE signing the quote or purchase order, usually by the programme’s partner contractor; no need to be a customer |
| Super-reduced 3% VAT rate | Saving of 14 VAT percentage points on the amount excluding VAT | Home at least 10 years old, main residence |
| Municipal grants | Varies (€500–3,000) | Depends on the municipality — ask your local municipal administration (commune) |
Worked example — house with an 80 m² unconverted attic, certified cellulose
Area to insulate: 80 m² of unconverted attic
Material: Certified bio-based cellulose, >50% recycled
Cost of the work incl. VAT (3% VAT): ~€55/m² × 80 m² = €4,400
― Theoretical maximum Klimabonus (attic floor, eco-friendly insulation, standard I): €65/m² × 80 m² = €5,200 (€75/m² × 80 m² = €6,000 if the approval in principle is requested before 30 June 2027)
⚠ The Klimabonus is capped at 60% of the cost of the work excluding VAT: 60% × ≈ €4,272 excl. VAT ≈ €2,563
→ Actual Klimabonus: ≈ €2,563
― Enoprimes: amount depends on the measure, to be simulated with the partner contractor (not counted here)
― VAT saving at 3% instead of 17% (14 points on ≈ €4,272 excl. VAT): ≈ €598, already deducted from the price incl. VAT above (not added to the total)
Total estimated grants (Klimabonus only): ≈ €2,563
Estimated out-of-pocket cost: ≈ €1,837 for 80 m² of unconverted attic, before Enoprimes and municipal grants (3% VAT already included in the price)
For a Klimabonus application covering only roof insulation (a single measure), no full energy audit is required. The simplified procedure applies: simply submit form DEPA-2026 on MyGuichet.lu together with the DESC sheet (description of the measure), a copy of the first building permit and the quote checked by the approved company or the energy advisor; the payment request is then made with the CONF-2026 sheet and the invoices. It is the most accessible route in the whole Klimabonus scheme. As soon as the renovation covers more than one element (for example roof + walls) or includes mechanical ventilation, energy advice from an approved energy advisor becomes compulsory; it is subsidised at €1,700 for a house (€2,000 if the approval in principle is requested before 30 June 2027). See the full steps and procedures so that you don’t miss any condition.
Work out your exact net cost after Klimabonus and Enoprimes. Free simulation in 2 minutes.
Estimate my grants →Roof insulation in Luxembourg: the procedure step by step
The Klimabonus procedure is strictly sequential. Doing the steps in the wrong order can mean losing all or part of the grants for good. For a complete guide to the energy renovation process, see our page on energy renovation steps and procedures in Luxembourg.
Estimate your grants and assess feasibility
Use our online simulator to estimate your Klimabonus and Enoprimes grants based on your surface area, your type of attic and your choice of insulation. This lets you weigh up the different methods and materials before contacting contractors.
Apply for Enoprimes BEFORE signing any purchase order
The Enoprimes file (a programme offered by Enovos and Sudenergie; you do not need to be a customer) is usually opened by the programme’s partner contractor, and it must be opened before you sign anything with your contractor (quote, purchase order or purchase of materials). This step is non-negotiable: once the order has been signed, the grant can no longer be applied for.
Get at least 3 quotes from certified contractors
Ask several approved contractors for quotes. The quote must state the material, its CE certification, its λ value, the planned thickness and separate costs for supply and installation. For a single measure, the Klimabonus requires the work to be carried out by a company approved under the law of 21 April 1993, or to be supported on site by an approved energy advisor.
Obtain the Klimabonus approval in principle on MyGuichet.lu — BEFORE the work
Submit your application using form DEPA-2026 on MyGuichet.lu. For insulation alone (simplified single-element procedure), the main document required is the detailed quote with CE-certified technical data sheets. Wait for written approval before signing your purchase order or starting the work.
Have the work carried out by a certified contractor
Once you have received the approval in principle, sign your purchase order. The work must be carried out in line with the specifications of the approved application: the same material, thickness and methods as those that were validated. Any substantial change requires a new application for approval.
Submit the payment request with supporting documents
Once the work has been completed and signed off, submit your payment request on MyGuichet.lu with: paid invoices, CE-certified technical data sheets, and photos of the work if requested. Payment is usually made within 4–12 weeks. For insulation, invoices must be dated between 1 January 2026 and 31 December 2035, and the first application for approval in principle must have been submitted by 31 December 2030 at the latest.
Klimabonus payment requests must be submitted within 4 years from 31 December of the year of the invoice. If your work is invoiced in 2026, you have until 31 December 2030 to submit the payment request. Incomplete or late applications are rejected, with no exceptions.
Common mistakes to avoid when insulating your roof in Luxembourg
Insulating the attic floor when you plan to convert the attic
This is the most expensive mistake in the long run. Insulating the floor of an attic you intend to convert in the next few years forces you to redo everything when the conversion takes place: insulating the sloping roof, removing the floor insulation — and you cannot claim the Klimabonus a second time for the same element. First decide how you will use your attic in the future, then choose the appropriate method.
Using non-compliant or non-CE-certified insulation
Only insulation bearing the CE marking with a certified λ value, laid to the required minimum thickness (20 cm for λ = 0.035 on roofs), is eligible for the Klimabonus. Insulation bought from DIY superstores without a certified data sheet, or reclaimed materials, will not qualify for grants. Ask for the performance data sheet before buying or installing anything — a missing or non-compliant data sheet means your application will automatically be rejected.
Neglecting airtightness and the vapour barrier
Even very thick insulation becomes largely ineffective if it is not combined with good airtightness. Air leaks carry heat away far faster than simple thermal conduction through the insulation. Insist that your contractor deals carefully with junctions, penetrations and the area around the hatch. A blower door test can confirm the final airtightness.
Insulating without checking the ventilation
When you make a home more airtight and better insulated, you reduce natural air changes. If your ventilation system is non-existent, inadequate or faulty, roof insulation can lead to problems with damp, condensation and indoor air quality. Have your ventilation checked before or during the insulation work.
Forgetting to check the roof structure before insulating
Insulating roof timbers attacked by wood-boring insects (house longhorn beetles, powderpost beetles, furniture beetles) or rotted by untreated leaks is a serious mistake. The insulation will trap moisture and speed up the deterioration. Have the roof structure surveyed before the insulation work — especially in Luxembourg houses built before 1980. Undetected damage to the roof timbers can cost 10 to 50 times more to put right afterwards.
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Frequently asked questions — roof and attic insulation in Luxembourg
How much is the Klimabonus for roof insulation in Luxembourg in 2026?
Since 1 January 2026, the Klimabonus for roof insulation has been a flat rate per m² that depends on the insulation material and the standard achieved: €60–85/m² for mineral insulation (glass wool, rock wool) and €90–115/m² for eco-friendly insulation (wood fibre, hemp, cellulose), plus €15/m² for mineral insulation with more than 50% recycled content or eco-friendly insulation from certified sources. On the floor of an unconverted attic, the grant is lower (€40–65/m² for eco-friendly insulation). These amounts are increased if the approval in principle is requested before 30 June 2027, and the grant is capped at 60% of costs excluding VAT.
How thick does the insulation need to be to qualify for the roof Klimabonus?
The minimum thickness required is 20 cm for CE-certified insulation with λ = 0.035 W/(m·K) (standard III), both on the roof and on the attic floor. In practice, to achieve the best performance, it is advisable to aim for 30–40 cm depending on the material: 30 cm of rock wool, 35 cm of cellulose or 25–30 cm of dense wood fibre. The thicker the insulation, the greater the comfort and the faster you recoup your investment.
What is the difference between an unconverted attic and a convertible attic when it comes to insulation?
An unconverted attic (loft) is a non-habitable space under the roof: it is insulated at floor level (blown-in insulation or rolls), at a cost of €35–70/m². A convertible attic is intended to be lived in: you insulate the sloping roof (boards between and under the rafters) or carry out sarking from outside, at a cost of €90–160/m² (sloping roof) or €180–350/m² (sarking). The choice depends on the current and planned future use of the space under the roof.
Can the Klimabonus be combined with Enoprimes for roof insulation?
Yes, the two grants can be fully combined. The Klimabonus is paid by the Luxembourg State (Environment Agency), while Enoprimes are offered by energy suppliers (Enovos and Sudenergie), and you do not need to be their customer. Note: Enoprimes must be applied for before you sign the purchase order with your contractor — if you sign first, they are lost for good.
What is sarking and when should you choose it in Luxembourg?
Sarking is a method of insulating a pitched roof from outside: rigid insulation boards are laid over the roof structure, under a new roof covering. It is the highest-performing method (no thermal bridges) but also the most expensive (€180–350/m² all-inclusive). In Luxembourg, sarking is recommended in three situations: (1) you need to replace your roof covering anyway, (2) you want to keep all of the interior space in your attic, (3) you are aiming for a very high level of performance (passive house).
Do you need a municipal permit to insulate a roof in Luxembourg?
Insulation from inside (blown-in insulation in an unconverted attic, boards under the sloping roof) does not usually require municipal permission in Luxembourg. Sarking, on the other hand — which slightly alters the volume and sometimes the appearance of the roof — may require a building permit, particularly in historic town centres, protected sites or areas covered by a PAP. Always check with your municipal administration before starting a sarking project.
Does the 3% VAT rate apply to roof insulation work?
Yes, for homes completed at least 10 years ago, the super-reduced 3% VAT rate applies to energy renovation work, including roof insulation. That is a saving of 14 percentage points compared with the standard 17% rate. For more details on the conditions, see our guide to 3% VAT on renovation work in Luxembourg.
How long does it take to insulate an unconverted attic?
For an unconverted attic of 80–120 m² insulated with blown-in insulation, the job usually takes just one day. You do not need to leave your home or empty the rooms. It is one of the least disruptive energy renovation jobs. Insulating under the sloping roof takes 3–7 days depending on the area and complexity. A full sarking job (removal of the roof covering + insulation + new covering) takes 1–3 weeks depending on the size of the roof.
How long does roof insulation last in Luxembourg?
Lifespan depends on the material: mineral wool (glass or rock) lasts 30–50 years before it settles and loses performance. Wood fibre can last up to 60 years with good moisture management. Cellulose resists settling well and lasts 40–50 years. In all cases, it is advisable to check the remaining thickness after 25–30 years, particularly in unconverted attics with blown-in insulation.
Can you insulate the roof of an occupied home without moving out temporarily?
In the vast majority of cases, yes. Insulating an unconverted attic (blown-in) or insulating under the sloping roof does not require you to move out. Only sarking may need special care in bad weather (risk of rain while the roof covering is off), but the contractor puts temporary protection in place. On flat roofs, the work is done entirely from outside, with no disruption to the occupants.
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