Where does glass wool fit?
Glass-wool rolls and slabs can suit insulation from inside, between roof timbers. Select a product specified for that application. It should fit without gaps and retain the specified thickness; compressing an oversized layer to fit the cavity does not reproduce the intended build-up.
Assess the existing layers first
An impermeable outer layer, existing insulation or leakage can change the specification. Unfaced wool and foil-faced wool do not automatically need the same membranes. Assess moisture behaviour and detail airtight junctions at walls, windows and cables. A variable vapour-control membrane is not a universal remedy for a damp roof.
Comparing glass wool and stone wool
Compare products at the same target thermal resistance. Required thickness, fit, installation method and tested acoustic performance of the complete construction matter. The material name alone does not establish the sound insulation or fire resistance of the finished roof.
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Checked on 23 September 2026.