Roof Insulation Luxembourg 2026: Glass Wool, Wood Fibre or Cellulose?

Why roof insulation matters in Luxembourg

In Luxembourg, a poorly insulated house can lose up to 30% of its heat through the roof. With harsh winters and increasingly hot summers, choosing the right roof insulation is crucial for both your comfort and your energy bills. The Klimabonus Wunnen 2026 programme, which replaced PRIMe House in January 2026, offers substantial support: up to 50% of roof insulation costs, capped at 15,000 EUR, provided you achieve a thermal resistance R ≥ 6 for sarking or R ≥ 7 for lost attics. The super-reduced VAT rate of 3% also applies to homes over two years old. In this comparison, we review three major insulants: glass wool, wood fibre and cellulose wadding. You will discover their performance, costs and benefits to make an informed choice.

Glass wool: the classic, economical insulation

Glass wool is made from sand and recycled glass, melted and spun into fibres. It is the most common insulation in Europe, thanks to its attractive price and ease of installation. It comes in rolls or panels, with thermal conductivity (lambda) between 0.032 and 0.044 W/m·K. To achieve R ≥ 6 required by Klimabonus Wunnen, you need a thickness of 22 to 26 cm. Its main advantages:

• Controlled cost: 15 to 30 EUR/m² supplied and installed, making it the most affordable option.
• Good thermal performance: ideal for lost attics or rafters.
• Immediate availability: all Luxembourg suppliers keep it in stock.
• Non-combustible: A1 classification (does not spread flames).

However, glass wool has limitations: its low thermal lag (about 4 to 6 hours) makes it less effective in summer, and it can lose efficiency if compressed or damp. It is also irritating during installation, requiring protective equipment. For a south-facing roof, it should be combined with a high-performance vapour barrier.

Wood fibre: ecological performance and summer comfort

Wood fibre is made from softwood fibres, bound with natural additives (starch, lignin). It is particularly appreciated for its environmental credentials: renewable material, low-energy manufacturing and carbon storage. Its thermal conductivity ranges from 0.036 to 0.042 W/m·K, with a thickness of 22 to 25 cm for R = 6. Its advantages are numerous:

• Excellent thermal lag (10 to 12 hours): keeps the house cool in summer and warm in winter.
• Natural moisture regulation: wood fibre absorbs and releases water vapour, preventing condensation.
• Durability: 30 to 50 years if protected from moisture.
• Acoustic comfort: effectively reduces outside noise (rain, wind).

Its main drawback remains its high price: expect 25 to 50 EUR/m² supplied and installed, up to twice as expensive as glass wool. It is also sensitive to moisture and must be installed with a suitable vapour barrier. For sarking roofs, it is often preferred for its summer performance, but requires specific expertise.

Cellulose wadding: the smart compromise

Cellulose wadding is made from recycled paper (newspapers, cardboard) shredded and treated with boron salts (fire retardants and fungicides). It comes loose, to be blown or sprayed. Its thermal conductivity is between 0.038 and 0.041 W/m·K, with a thickness of 23 to 25 cm for R = 6. It is an excellent compromise between performance, ecology and price:

• Unbeatable value for money: 20 to 35 EUR/m² supplied and installed.
• Very favourable carbon footprint: made from waste, low embodied energy.
• High thermal lag (8 to 10 hours): summer comfort close to wood fibre.
• Seamless application: perfectly fills irregularities, limiting thermal bridges.

Cellulose wadding is sensitive to moisture: it must be installed with a hygrovariable vapour barrier and effective ventilation. Its installation requires a specific machine, so a professional is needed. It is ideal for lost attics, but can also be used in rafters or sarking with caissons.

Comparison table: glass wool, wood fibre and cellulose wadding

This table highlights the trade-offs. Glass wool remains the most affordable, but wood fibre and cellulose offer better summer comfort and reduced environmental impact. The choice will depend on your budget, roof configuration and priorities.

Selection criteria: how to decide?

To choose the right insulation, several factors come into play:

• Your budget: glass wool is unbeatable, but Klimabonus Wunnen 2026 aid reduces the gap. With a 50% subsidy capped at 15,000 EUR, wood fibre can become competitive.
• Your roof configuration: lost attics, rafters, sarking? Cellulose wadding is ideal loose-fill for lost attics, while wood fibre is often preferred for sarking due to its summer performance.
• Your priority: pure thermal performance (glass wool), summer comfort (wood fibre), or ecological and economic balance (cellulose).
• Required thermal resistance: to benefit from Klimabonus, you need R ≥ 6 for sarking and R ≥ 7 for attics. Check that the chosen insulation can achieve these values with a reasonable thickness.
• Installation: some insulations require a professional (cellulose), others can be installed by an experienced DIYer (glass wool rolls).

Remember that the 3% VAT rate applies to renovation works in homes over two years old, which reduces the bill. For all conditions, consult Guichet.lu and Klima-Agence.

Klimabonus Wunnen 2026: a significant boost

Since January 2026, the Klimabonus Wunnen programme has replaced PRIMe House. It aims to encourage energy renovation of homes in Luxembourg. For roof insulation, the aid covers 50% of costs, with a cap of 15,000 EUR. Conditions: achieve a thermal resistance R ≥ 6 for sarking insulation (between rafters) and R ≥ 7 for lost attics. Works must be carried out by a certified craftsman and be subject to a prior application. Other aids exist:

• Photovoltaic panels: up to 10,000 EUR (about 8,300 EUR for 10 kWp, maximum reached from 15 kWp).
• Home battery: up to 2,250 EUR.
• Windows: 70 EUR per m² of glazing replaced.

These subsidies can be combined with the 3% VAT and other possible aids. To benefit, you must submit an application to the competent administration. The website klima-agence.lu details the procedures. Also remember to comply with data protection regulations (CNPD) if you share personal information.

Typical example: how much does roof insulation cost in Luxembourg?

Let's take an illustrative case: a 150 m² detached house in Luxembourg City, with 100 m² of lost attics to insulate. The owner aims for R = 7 to benefit from Klimabonus Wunnen. Here is a cost estimate:

• Glass wool: 100 m² x 25 EUR/m² = 2,500 EUR. 50% aid = 1,250 EUR. Remaining cost: 1,250 EUR (excluding reduced VAT).
• Wood fibre: 100 m² x 40 EUR/m² = 4,000 EUR. 50% aid = 2,000 EUR. Remaining cost: 2,000 EUR.
• Cellulose wadding: 100 m² x 30 EUR/m² = 3,000 EUR. 50% aid = 1,500 EUR. Remaining cost: 1,500 EUR.

This example shows that, thanks to subsidies, the price gap narrows considerably. Cellulose wadding becomes very competitive, with superior summer comfort. Note that these amounts are indicative and vary depending on the craftsman, site complexity and finishes.

Conclusion: which insulation for your roof in Luxembourg?

There is no single answer. If your budget is tight and you are insulating lost attics, glass wool remains a pragmatic choice. If you seek summer comfort and an ecological approach, wood fibre is excellent, but more expensive. Finally, cellulose wadding offers the best compromise between price, performance and environmental respect. In all cases, check the conditions of Klimabonus Wunnen 2026 to maximise your aid. Use a certified professional to ensure proper installation and benefit from subsidies. To go further, consult our guides on attic insulation and sarking.