What is the best insulation for a pitched roof?

PIR boards provide the highest insulation value per centimeter of thickness and are therefore popular when rafter depth is limited. Glass or rock wool is cheaper, vapor-permeable, and acoustically better, but requires more thickness for the same R-value (Rc). The choice depends on available space, budget, and acoustic requirements.

What R-value (Rc) should loft insulation achieve?

For newly installed roof insulation, the Besluit bouwwerken leefomgeving requires a minimum R-value (Rc) of 6.3 m²K/W. For existing buildings, the minimum is lower, but with major renovations, the new-build value is maintained in practice.

Is a vapor barrier foil always necessary?

With dense insulation (PIR with properly sealed seams, or injected cellulose) and correctly detailed connections, a separate vapor barrier foil can sometimes be omitted. In most situations with mineral wool, however, a vapor barrier on the warm side is necessary to prevent condensation in the structure.

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Insulating a loft is in many cases the most impactful sustainability measure for a home. Heat loss through the roof is significant, and good roof insulation significantly lowers the heating bill and increases comfort.

Hoofdgids · 15 min lezenZolderverbouwing: complete gids

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What to insulate

The pitched roof, between or under the rafters.
The knee walls and the floor behind the knee walls.
The floor below the loft, if the loft itself remains unheated.

Insulation principle

Good insulation means not only sufficient thickness (R-value (Rc)), but also an airtight finish on the warm side, ventilation on the cold side, and an uninterrupted insulation shell without cold bridges.

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What is the best insulation for a pitched roof?
PIR boards provide the highest insulation value per centimeter of thickness and are therefore popular when rafter depth is limited. Glass or rock wool is cheaper, vapor-permeable, and acoustically better, but requires more thickness for the same R-value (Rc). The choice depends on available space, budget, and acoustic requirements.
What R-value (Rc) should loft insulation achieve?
For newly installed roof insulation, the Besluit bouwwerken leefomgeving requires a minimum R-value (Rc) of 6.3 m²K/W. For existing buildings, the minimum is lower, but with major renovations, the new-build value is maintained in practice.
Is a vapor barrier foil always necessary?
With dense insulation (PIR with properly sealed seams, or injected cellulose) and correctly detailed connections, a separate vapor barrier foil can sometimes be omitted. In most situations with mineral wool, however, a vapor barrier on the warm side is necessary to prevent condensation in the structure.