Mineral fibre (fire-stop)
Mineral fibre is non-combustible inorganic fibre (rockwool, glass-wool) packed around service penetrations through fire-rated walls. Maintains FRL up to 2,000 mm².
Ask Chalkline about this →Mineral fibre in the building-compliance context is a non-combustible inorganic fibre packing material, typically stone wool (rockwool) or glass-wool, used to pack small openings around service penetrations through fire-rated separating walls. The material preserves the Fire Resistance Level (FRL) of the wall at the penetration without requiring a full proprietary fire-stop seal. Under NCC 2022 Volume Two Housing Provisions 9.3, mineral-fibre packing is permitted for cable penetrations up to 2,000 mm² per cable, where the wall opening is closely fitted around the cable (verified 2026-05-16).
Where it applies in residential:
- Fire-rated separating wall between sole-occupancy units in Class 2 apartment buildings.
- Garage-to-dwelling wall in Class 1a where it must be fire-rated (most NSW dwellings under NCC 2022).
- Wall between attached dwellings (semi-detached, duplex) where the party wall is fire-rated.
- Floor-to-floor penetration through a fire-rated separating floor in multi-storey Class 2.
What mineral fibre is NOT (the common confusion):
| Compared to | Mineral fibre fire-stop | The other thing |
|---|---|---|
| Bulk thermal insulation | Used for fire-stopping small service penetrations | Used to fill cavity for thermal R-value (AS/NZS 4859) |
| Intumescent fire-stop putty | Cheap, packs small openings | Higher-performance proprietary system, larger openings |
| Fire-stop pillows / pillows | Loose packing | Proprietary bagged product for larger penetrations |
| Fire collar (for plastic pipes) | Not applicable | Required for combustible-material penetrations (plastic, PE-X) |
The material itself can be the same physical product (rockwool batt) as bulk thermal insulation in a normal wall, but its fire-stop use is a distinct application with specific install rules.
Install rules for mineral-fibre fire-stop:
- Cable opening must be small (under 2,000 mm² per cable, e.g. one or two cables per opening).
- Mineral fibre is packed tight to fill the entire annulus around the cable.
- No air gaps between cable and fibre, no gaps between fibre and surrounding wall material.
- Multiple-cable bundles require larger fire-stop solutions (proprietary collar, putty, intumescent seal) per the manufacturer’s tested system.
- Plastic-sheathed cables above the threshold size require a tested intumescent collar, not mineral fibre alone.
- Combustible pipework (PE-X, PVC) requires a tested fire collar, not mineral fibre.
Common defects to look for at frame inspection:
- Cable hole at the right size but packed with standard bulk insulation (e.g. R3.5 batt) rather than fibre offcut from a non-combustible product. Verify the product is non-combustible.
- Cable hole oversized to “make it easier to pull cable”, with mineral fibre stuffed loosely, leaving an air path and compromising the FRL.
- Sparky’s “rough hole” cut large for future cabling, never packed at install. Becomes a frame inspection fail.
- Plastic pipe penetration with mineral fibre only and no fire collar. Pipe burns through; FRL fails.
Also known as: stone wool fire-stop; glass-wool fire-stop; non-combustible fibre packing.
Category: Compliance.
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Last updated: 2026-05-16. Verified: 2026-05-16. Quarterly review for currency.