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Thomas R.Mons
Insulation · Unused loft
Attic insulation: the most cost-effective move in any renovation
An unused loft (an unconverted attic) is heat escaping through your roof for nothing. Blowing insulation across the loft floor is the quickest move (just a few hours), the cheapest per m² and one of the most effective. If your loft is unused, this is where to start.
- A few hours
- to install
- From €15/m²
- material + fitting
- Cellulose · wool
- blown in
In a few hoursthe fastest install
From €15/m²the cheapest option
Methods
How do you insulate an unused loft?
The principle is simple: you insulate the loft floor, not the slope of the roof.
- Blowing The go-to method
A hose blows cellulose (recycled paper) or wool (glass, rock) in loose flakes across the loft floor. Fast, even, no cutting required.
- Rolls Alternative
Rolls of mineral wool unrolled across the floor. Slower than blowing but lets you walk on it (with a walkway board).
- Thickness 25–35 cm
To reach R ≥ 6 (above the grant threshold), 25 to 35 cm of cellulose or wool is blown in, depending on the material’s lambda.
- Cellulose Eco-friendly
Cellulose wadding is made from recycled newsprint. Excellent carbon footprint, good summer comfort (thermal lag), treated against fire and mould.
- Summer comfort Excellent
The generous depth of blown insulation delivers excellent thermal lag: the loft and the ceiling stay cool in summer.
- Condition Unused loft
Blowing makes the loft non-walkable (apart from a walkway). If the loft is converted or due to be, see roof insulation instead.
* Indicative values. The exact thickness is calculated during the on-site survey.
Full transparency
Upsides & limits of blown loft insulation
Blowing is unbeatable on speed and cost, but it has one condition: the loft must not be in use.
Where it shines
- Cheapest per m²From €15/m² in blown cellulose. The best cost-to-gain ratio in all of insulation.
- Fitted in a few hoursA typical house is blown in half a day. No major works.
- No cuttingBlown insulation hugs every shape, fills the corners and surrounds the ducts.
- Eco-friendly (cellulose)Recycled paper, low embodied energy, excellent thermal lag.
What you should know
- Loft no longer walkableYou can’t walk on blown insulation anymore. Plan a walkway if needed.
- Not for converted loftsIf the loft is lived in or due to be, the slope must be insulated (roof insulation).
- Possible settlingBlown insulation settles slightly over the years. We blow to target depth plus a settling margin.
- Loft access requiredA hatch or access point is needed for the blowing hose.
For which loft
Is blowing right for your loft?
If your loft is unused, blowing is the first move to make.
-
Unconverted attic
The ideal case: an empty attic, an access hatch and a few hours of blowing. The thermal gain is immediate.
-
Insufficient old insulation
A bit of wool laid 30 years ago? We blow over it to top up the depth. No need to remove the old layer.
-
Co-ownership
A building’s loft is often unused. Blowing covers the whole building in a single day.
Converted loft?
If your loft is lived in or meant to be, blowing isn’t suitable. See roof insulation (between or over the rafters). And compare the materials to pick the right insulant.
Glissez la poignée pour comparer
Case study · detached house, Tournai
80 m² of loft blown in 3 hours
An 80 m² unused loft, never insulated. We blew in 30 cm of cellulose in 3 hours. The top-floor ceiling temperature rose 4 °C in the first winter. Cost: around €1,600 before grants.
- 3 hoursfor 80 m²
- +4 °Cat the ceiling
- ~€1,600before grants
Customer reviews
They chose wendows
4.5/5 · 2verified reviews
« Insufflation des murs creux, rapide et sans dégât. La prime régionale a couvert une bonne part. Maison nettement moins froide. »
David K.Huy
Compare
Blowing, rolls or roof insulation?
The choice depends on how your loft is used.
| Critère | Loft blowingVous êtes ici | Loft rollsVoir la gamme → | Roof insulationVoir la gamme → |
|---|---|---|---|
| Price | The gentlest | Gentle | Higher |
| Speed | A few hours | 1–2 days | 2–5 days |
| Loft walkable | No | With a board | Yes (converted) |
| Loft convertible | No | No | Yes |
| Performance | Excellent | Very good | Very good |
| Summer comfort | Excellent (cellulose) | Good | Variable |
| Best for | Unused loft, budget | Unused loft + access | Converted loft |
Indicative benchmarks. If the loft is converted, blowing isn’t suitable.
- if converted
Roof insulation
For converted lofts: insulation between or over the rafters.
See the roof → - next step
Wall insulation
After the loft, the walls are the second priority.
See the walls → - which material
Materials
Cellulose, glass wool, rock wool: compare them.
Compare → - complement
Floor insulation
The floor accounts for 10% of losses. Often done from the cellar.
See the floor → - to combine
Heat pump
Insulate before installing a heat pump — so you don’t oversize it.
See heat pumps → - ↑ category
All insulation
An overview of our insulation solutions in Belgium.
Back to the guide →
Indicative pricing 2026
How much does loft insulation cost?
Blowing is the cheapest insulation move per m².
See detailed insulation pricing →* Indicative ranges per m² fitted. The exact price depends on access and thickness.
- Blown cellulose €15–25/m²25–30 cm blown in
- Blown wool €18–30/m²25–35 cm blown in
- Mineral wool rolls €20–35/m²in 2 crossed layers
- Renovation grant up to 35%depending on income and region
Loft FAQ
Your questions about loft insulation
Can you still walk in the loft after blowing? +
No, not directly on the insulation. A walkway (boards on the joists) can be planned to reach the hatch, the meter or the ventilation unit. The rest stays covered.
Do you need to remove the old insulation? +
Not necessarily. If the old insulation is dry and in good condition, we blow over it to top up the depth. If it’s damp or mouldy, we remove it first.
Is cellulose flammable? +
Cellulose wadding is treated with a flame retardant (boron salt). It does not spread flame and chars slowly. It meets fire standards for use in lofts.
Does blown insulation settle over time? +
Slightly (5–10% over the first few years). That’s why we blow with a built-in settling margin. Performance stays compliant over time.
How long does the work take? +
For a typical house (60–100 m² of loft), blowing takes 2 to 4 hours. No disturbance for the neighbours, no structural work.
What grants are there for lofts? +
Regional grants apply as soon as the U-value meets the threshold (Umax 0.24 W/m²K, easy with blowing). VAT at 6% on renovation. Blowing is the most heavily subsidised move relative to its cost.
Get your free loft quote within 48h
Free loft visit, choice of material, grants calculated. Describe your project in under a minute.
- Free and no obligation
- Grants & 6% VAT handled for you
- Fitted in a few hours