PIR / PUR — maximum insulation at minimum thickness
With little spare height: ± 12 cm. Little height and a high thermal resistance needed? Then we combine PIR with glass wool.
- λ W/m·K
- 0,022–0,025
- Thickness
- ± 12 cm with little spare height
Roofs / Roof insulation
Roofs · insulation Roof insulation
A poorly insulated roof can waste up to 35% of your home's heat. Good insulation makes your home warm, energy-efficient and healthier — and increases its value.
- Up to 35%heat loss through the roof
- λ 0,022PIR at minimum thickness
- 3 materialsPIR, glass wool, stone wool
Warmth and comfort stay inside A solution tailored to your roof.
With a well-insulated roof you save on energy costs, enjoy a healthier indoor climate and ensure lasting comfort for your family.
We tailor every solution to your home — taking into account the roof structure, the budget and the specific conditions. Our work aims for results that last for decades.
- Inside, outside or a combination
- According to available height
- Together with underlay and vapour barrier
Roof insulation · PIR / PURWhich material? How much space do you have?
A poorly insulated roof can waste up to 35% of your home's heat. A fully renovated pitched roof consists of four layers: the roof covering, the underlay, the insulation layer and a vapour control layer on the inside. Which insulation material we choose depends on the available height, the substrate and the roof covering.
Glass wool — between the rafters, good for acoustics
Classic insulation between the rafters, with good sound damping.
- λ W/m·K
- 0,030–0,040
- Guide value
- 20–22 cm
Stone wool — increased fire resistance
For load-bearing structures and wherever fire safety matters most.
- λ W/m·K
- 0,032–0,040
Four layers, in this order
During the site visit we inspect the roof structure, the underlay, the insulation, the rainwater drainage and the connections. Only then do we choose the build-up. Gutters, roof windows and the connections to the chimney and façade are finished in the same job.
- Roof covering: tiles or slates
- Underlay: water and wind barrier, vapour-open
- Insulation layer
- Vapour control layer inside
Build-up height, the condition of the substrate and the chosen roof covering determine the final build-up — we check this for every project.
The build-up The roof as one system.
The insulation retains the heat, the vapour control layer limits moisture from inside and the underlay protects against water and wind while staying vapour-open.
- 01Roof covering
Roof tiles or slates
- 02Underlay
Water and wind barrier, vapour-open — with counter battens and tile battens
- 03Insulation layer
PIR, glass wool or stone wool — according to height and substrate
- 04Vapour control layer
On the inside, limits moisture penetration from inside
Practical scenarios in Belgium The space determines the choice.
- ✓
Raising the roof is often not possible: glass wool between the rafters, guide value 20–22 cm.
- ✓
Little height and a high thermal resistance needed: a combination of PIR and glass wool.
- ✓
Maximum insulation at minimum thickness: PIR boards, also for flat sections; PUR foam for airtight connections.
- ✓
Fire safety important: stone wool, for load-bearing structures.
Projects Roofs we insulated.
In Andenne we laid 230 m² of natural slate on 12 cm of PIR insulation — in two weeks.
26cities in 6 provinces
from Bruges to Namur
The materials Three materials, three strengths.
PIR for the best insulation at low thickness, glass wool for acoustics between the rafters, stone wool for fire resistance.
Grants and financing
We check what you are entitled to.
Since 2026, roof insulation in Flanders only qualifies for Mijn VerbouwPremie in income categories 3 and 4. We check your situation, help with the application and, if you wish, arrange a renovation loan through KBC.
Questions about roof insulation What our clients ask us.
How much heat do I lose through the roof?
A poorly insulated roof can waste up to 35% of your home's heat.
Which insulation is best?
That depends on the space: PIR/PUR insulates best at a small thickness, glass wool is good for acoustics between the rafters and stone wool is more fire-resistant. With little height, we combine PIR with glass wool.
How thick does the insulation need to be?
With little spare height ± 12 cm of PIR; glass wool between the rafters has a guide value of 20–22 cm. We check the final thickness for each project.
Can I get a grant for roof insulation?
In Flanders, since 2026 roof insulation only qualifies for the Mijn VerbouwPremie grant in income categories 3 and 4. We review your situation and help with the application.
Free site visit · quote within 48 hours Ready for
a warm roof?
Our specialist inspects your roof and sends you a tailored, no-obligation quote within 48 hours.
- Phone
- +32 333 20 630
- leads@gravagroup.be
- Address
- Sneeuwbeslaan 14, 2610 Wilrijk
Free 3D visualisation with your quote