BREATHABLE UNDERLAY
To achieve the required U-value of 0.18 W/m².K the rafters need to be battened to increase the depth to 125mm. Rigid insulation is installed between the rafters, leaving a small unventilated air space below the membrane.
If there is insufficient head room to batten out the rafters, then a lesser U-value may be acceptable.
Solutions with PIR: TLX Silver BM PIR
Solutions with mineral wool: TLX Silver BM Wool

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