Under-rafter insulation
Converted or convertible attics — mineral wool or wood fibre between and under rafters. Thickness 200 to 280 mm for R ≥ 6. Interior vapour barrier mandatory (Sd ≥ 18 m). Plasterboard or panelling finish.
Thermal insulation — AtticAttic
Attic
Insulation
Under rafters and loft floor — Rockwool, Knauf, ISOVER, STEICO. R ≥ 6 to R ≥ 7 depending on configuration. QUASART insulates your attic in Luxembourg and the Greater Region.
R ≥ 6 raftersR ≥ 7 loftRockwool · Knauf · ISOVERMechanical blowing
30%Roof heat loss
R ≥ 7Loft target
4-8 yrsReturn on investment
Why the attic?
30% of heat loss through the roof — attic insulation is a priority.
The roof is the primary source of heat loss in a poorly insulated building — up to 30% of losses in winter. Conversely, it is often the most cost-effective intervention: unbeatable performance-to-cost ratio, work achievable without vacating living spaces, and a rapid return on investment.
QUASART, based in Crauthem (L-3327), handles all types of attic insulation in Luxembourg: converted attics (under-rafter insulation), loft spaces (blown-in or roll insulation on the floor) and convertible attics. Financial subsidies are available through the myenergy programme (Klimabonus) — visit myenergy.lu to check your eligibility.
Attic Insulation · Technical sheet
Données certifiéesCost-effectiveness10.0
Speed of execution9.0
Thermal performance9.5
Acoustic comfort8.0
Occupant disruptionMinimal
Lifespan40-50 years
Under raftersR ≥ 6 m²·K/W — 220-280 mm rock wool or wood fibre
Loft floorR ≥ 7 m²·K/W — 300-400 mm blown-in or rolls
Common insulantsRock wool (λ 0.035), glass wool (λ 0.032), cellulose wadding (λ 0.040), wood fibre (λ 0.038)
Mechanical blowingCellulose or mineral wool — 1 day for 100 m², uniform, no thermal bridges
Vapour barrierSd ≥ 18 m on warm side — mandatory under rafters, optional for loft floor
Weight3 to 8 kg/m² depending on insulation and thickness
DTU 45.10DTU 45.11EN 13162EN 14064ACERMIRE 2020 / GPE
Insulation materials
Four insulation materials for your attic
The choice of insulation depends on the type of attic, budget and targeted summer/winter performance.
01 / INSULATION MATERIALS
Rock wool
Rockwool Rockcomble, Alpharock — λ 0.035Thermal8.5
Acoustic9.0
Cost7.5
Non-combustible mineral insulation (A1). Excellent acoustic and thermal performance. Fire rating A2-s1,d0 in system. Available as panels, rolls and flakes for blowing.
Fire & acoustic02 / INSULATION MATERIALS
Glass wool
ISOVER Isoconfort, Knauf Unifit — λ 0.032Thermal9.0
Acoustic7.5
Cost9.0
Lowest lambda among mineral insulants (0.032). Lightweight, easy to install between rafters. Excellent performance-to-cost ratio. Flexible rolls for converted attics, flakes for loft blowing.
Economical03 / INSULATION MATERIALS
Cellulose wadding
UniverCell, Isocell — λ 0.039-0.042Thermal7.0
Acoustic8.0
Cost8.0
Recycled newspaper treated with borax. Fast mechanical blowing (1 day for 100 m²). Good thermal lag (summer comfort). Integrated fire and mould treatment.
Recycled04 / INSULATION MATERIALS
Flexible wood fibre
STEICO Flex, Gutex Thermoflex — λ 0.038Thermal8.0
Acoustic8.5
Cost5.5
Semi-rigid wood fibre panel — exceptional thermal lag (12-16h in attics). The ideal choice for converted attics under roofs where summer comfort is critical. Negative carbon footprint.
Bio-basedInterior finishes
From plasterboard to wood panelling.
The finish depends on the type of attic and the intended use of the space.
Standard
Standard BA13 boardPaint finish — converted attics
Moisture-resistant
Moisture-resistant BA13Bathroom under the roof
Natural
Natural wood panellingPine, fir — chalet style
White
White MDF panellingContemporary, bright appearance
Fermacell
Fermacell fibre-gypsumHigh mechanical resistance
No
No finish (loft)Unconvertible loft — exposed blown-in
Referenced manufacturers
Four manufacturers. Attic insulation mastered.
QUASART works with the European leaders in insulation.
Denmark · Fire referenceDenmark · Fire A1 · Acoustic
ROCKWOOL
Rockcomble · Alpharock · RockmurWorld leader in rock wool. Rockcomble (loft blown-in), Alpharock (semi-rigid panels under rafters), Rockmur (partitions). Non-combustible A1, excellent acoustic attenuation. Manufactured in Couvin (Belgium) — logistic proximity.
Rockcomble — loft blown-in insulation
Alpharock — semi-rigid panels under rafters
Non-combustible A1 — maximum fire safety
Manufactured Couvin (BE) — proximity to Luxembourg
Germany · High performanceGermany · ECOSE · Formaldehyde-free
KNAUF INSULATION
Unifit · TI 135 · SupafilComplete range for attics. Unifit 035 (high-performance rolls), TI 135 (rigid panels), Supafil (blown glass wool). ECOSE technology — plant-based formaldehyde-free binder. Eurofins Indoor Air Comfort Gold certified.
Unifit 035 — rolls lambda 0.035
TI 135 — rigid panels between rafters
Supafil — mechanical glass wool blowing
ECOSE — plant-based binder, formaldehyde-free
France · VersatilityFrance · Saint-Gobain · Distribution
ISOVER (Saint-Gobain)
Isoconfort · IBR · ComblissimoSaint-Gobain Isover range for attics. Isoconfort 35 (rolls, lambda 0.035), IBR (economical rolls), Comblissimo (blown glass wool). Wide distribution network, permanent availability in Luxembourg.
Isoconfort 35 — high-performance rolls
Comblissimo — fast mechanical blowing
IBR — economical loft rolls
Saint-Gobain network — permanent stock
Germany · Bio-basedGermany · Bio-based · Thermal lag
STEICO
Flex · Joist · ZellSemi-rigid wood fibre panels for converted attics. STEICO Flex (between rafters, lambda 0.038), Joist (floor), Zell (blown cellulose). Exceptional thermal lag — the premium choice for summer comfort under roofs.
Flex — semi-rigid between rafters
Zell — blown wood cellulose
Thermal lag 12-16h — summer roof comfort
PEFC · Nature Plus · Negative carbon footprint
Types of intervention
Under rafters or floor — two complementary approaches.
Loft blown-in insulation
Cellulose wadding or mineral wool mechanically blown — thickness 300 to 400 mm for R ≥ 7. Fast technique (1 day for 100 m²), perfectly uniform, zero thermal bridges. No scaffolding required.
Floor rolls
Manual laying of glass wool or rock wool rolls on the loft floor. Economical solution for open surfaces. Thickness 300 to 360 mm, cross-laid in two layers.
Wood fibre between rafters
STEICO Flex semi-rigid panels between rafters — optimal thermal lag. Ideal for converted attics in timber-frame houses and high summer performance projects.
Hatch & singular points
Insulated and sealed access hatch (forgotten thermal bridge = 10% of losses). Chimney ducts, ventilation, recessed lights — every singular point is carefully treated.
Subsidies & grants
Financial subsidies are available through myenergy (Klimabonus) for attic insulation. Return on investment is estimated at 4 to 8 years depending on configuration. Visit myenergy.lu.
Installation process
Attic insulation steps
Installation differs depending on the type of attic — converted or loft.
01
Survey & diagnosis
Roof structure inspection, rafter spacing measurement, verification of under-roof ventilation. Identification of singular points (hatch, ducts, ventilation).
Structure · Ventilation · Singular points02
Insulation installation
Under rafters: semi-rigid panels wedged between rafters + additional layer below if necessary. Loft: mechanical blowing or cross-laying of rolls.
Rafters · Blowing · Cross-laid03
Vapour barrier & airtightness
Vapour barrier membrane on the warm side (Sd ≥ 18 m) under rafters — taped at junctions, sealed to walls. Loft: no vapour barrier if ventilated.
Sd ≥ 18 · Tape · Junctions04
Finishes
Under rafters: metal framework + BA13 plasterboard or panelling. Loft: thickness control gauge, hatch marking, signage panel.
BA13 · Panelling · ControlTechnical standards
Standards & certifications
Every QUASART attic insulation complies with applicable DTU standards and regulations.
DTU 45.10
Blown-in insulation
DTU standard for loft insulation by mechanical blowing — minimum thickness, installation density, control benchmarks.
DTU 45.11
Panel/roll insulation
DTU standard for panel and roll insulation in attics — layout, jointing, vapour barrier, singular points.
EN 13162
Mineral wool
European standard for mineral wool insulation products — declared lambda, thermal resistance, mechanical strength, water behaviour.
EN 14064
Blown-in insulants
European standard for loose-fill insulants (cellulose, blown wool) — installation density, settling, long-term thermal resistance.
ACERMI
Performance certification
French thermal performance certification — certified lambda, ISOLE rating. Guarantee that the installed product achieves stated performance.
RE 2020 / GPE
Energy performance
European and Luxembourg regulations — minimum R-value required for attics depending on climate zone and building type.
Areas of application
Attic insulation — for which buildings?
01
Detached houses — converted attics
Under-rafter insulation between and below rafters. STEICO Flex or Rockwool Alpharock for optimal thermal lag. The most common project in Luxembourg — 1 to 3 days depending on area.
02
Loft spaces — fast blowing
Mechanical blowing of cellulose or mineral wool in one day. The most cost-effective insulation solution: reduced cost, R ≥ 7 easily achieved, no occupant disruption.
03
Apartment buildings — upper floor
Insulation of the upper floor of the last inhabited level (communal loft). Coordinated intervention with the property manager. Reduced heating charges for all top-floor co-owners.
04
Commercial & public buildings
Insulation of office, school and retail attics. Rockwool rock wool required for A2-s1,d0 fire rating. Intervention possible outside business hours.
Selected projects
Attic insulation in practice
STEICO Flex 240mm between rafters
Under rafters · 2024Villa BridelBridel, Luxembourg
ISOVER Comblissimo blown 350mm
Loft · 2024House BertrangeBertrange, Luxembourg
Rockwool Rockcomble blown 400mm
Collective · 2023Residence GasperichGasperich, Luxembourg
Knauf Unifit 035 under rafters
Renovation · 2024House StrassenStrassen, Luxembourg
Rockwool Alpharock 280mm
Commercial · 2023Office KirchbergKirchberg, Luxembourg
Blown cellulose wadding 380mm
Residential · 2023House ThionvilleThionville, France
Attic insulation is often the first renovation step — and the most cost-effective. 30% of heat loss eliminated in one to three days of work.QUASART — Philosophie de la mise en œuvre
FAQ
Attic insulation FAQ
Everything you need to know
The Grand Ducal regulation and myenergy criteria recommend R ≥ 6 m²·K/W for converted attics (under rafters) and R ≥ 7 m²·K/W for loft spaces. These values correspond to approximately 220-240 mm and 280-300 mm of rock wool respectively.
Yes — this is the standard configuration. Insulation is carried out from the attic space, without any intervention in the occupied rooms. For loft spaces, mechanical blowing is completed in a few hours through the access hatch.
Glass wool has a slightly better lambda (0.032 vs 0.035) and is cheaper. Rock wool is non-combustible (A1), denser (better acoustics) and moisture-resistant. QUASART recommends rock wool for converted attics and blown glass wool for loft spaces.
Settling of 15 to 20% is normal in the first year. This is why EN 14064 requires an increased installation thickness (e.g. 350 mm installed to achieve 300 mm stabilised). QUASART systematically applies the manufacturer-recommended excess.
Financial subsidies exist in Luxembourg for attic insulation work. The myenergy programme (Klimabonus) can cover part of your investment. Visit myenergy.lu to check your eligibility and current conditions.
Under rafters (converted attics): yes, a vapour barrier on the warm side (Sd ≥ 18 m) is mandatory to prevent condensation in the insulation. Ventilated loft spaces: generally no — the natural ventilation of the loft is sufficient to evacuate water vapour.
Areas of operation