Repair Systems — 04
Sarking systems — mineral wool under-tile insulation
Technical product reference for glasswool and stone mineral wool insulation for pitched tiled roof ceiling and rafter applications. Covers Bradford Gold glasswool, Knauf Earthwool, and ROCKWOOL — NCC R-value requirements, fire performance, vapour permeability, and climate zone selection.
What are mineral wool under-tile insulation systems?
Mineral wool under-tile insulation covers glasswool batts (Bradford Gold, Knauf Earthwool) and stone mineral wool (ROCKWOOL) used in pitched roof rafter and ceiling applications. These are fibrous insulation materials installed between the ceiling joists or between the rafters of a pitched tiled roof to provide thermal insulation. Unlike PIR rigid boards, mineral wool batts are flexible and are not rigid — they compress to fit the available joist or rafter depth but must not be compressed to the point where R-value is reduced.
Product Reference
3 products — 3 brands — mineral wool under-tile insulation — scroll to view all
Bradford Gold Glasswool Batts
Glasswool mineral wool batt — ceiling / rafter — AS/NZS 4859
System Description
Bradford Gold is CSR Bradford's primary range of glasswool batt insulation products for residential and strata building applications, including pitched roof ceiling and rafter insulation. Bradford Gold batts are installed between the ceiling joists (at ceiling level) or between the rafters (at rafter level below the tile course) to provide thermal insulation. For pitched tiled roof applications, the standard installation is at ceiling level between the ceiling joists below the sarking and above the ceiling lining. Rafter-level installation requires tile removal and is typically combined with a re-tiling scope. Bradford Gold is available in R2.5, R3.5, R4.0, and R6.0 thicknesses — the required R-value is confirmed from the NCC climate zone requirement for the project location. Bradford Gold is the most widely distributed glasswool batt product in Australia, available through trade suppliers and Bunnings nationally. Glasswool batts are vapour-permeable and do not restrict moisture vapour movement within the roof assembly — this is an important characteristic when specifying insulation in a pitched roof assembly with sarking.
Technical Properties
- Glasswool batt — spun glass fibre mineral wool insulation
- Available in R2.5, R3.5, R4.0, and R6.0 — confirm current range from Bradford TDS
- Installed at ceiling level between joists or at rafter level between rafters
Limitations
- Not a rigid board — cannot be installed under-tile as a rigid substrate the way PIR or phenolic boards can — glasswool batts are installed between joists or rafters, not across them as a rigid layer
- Glasswool is combustible — confirm fire rating requirements with the building certifier for the specific roof assembly before specifying
- Must be installed without compression — compressing glasswool batts reduces their R-value — confirm that the available joist or rafter depth is sufficient for the specified R-value without compression
PROCUREMENT SOURCES
Confirm suitability with the current manufacturer TDS before specifying or applying.
Knauf Earthwool
Glasswool mineral wool batt — formaldehyde-free — AS/NZS 4859
System Description
Knauf Earthwool is Knauf Insulation's glasswool mineral wool batt product for residential and commercial insulation applications, including ceiling and rafter insulation in pitched roofs. Earthwool is manufactured with a formaldehyde-free ECOSE Technology binder — a bio-based binder that replaces the traditional phenol-formaldehyde binders used in conventional glasswool. This makes Earthwool a preferred choice for projects where formaldehyde-free insulation is specified, such as where occupant health is a priority or where the building's sustainability rating scheme requires low-VOC or formaldehyde-free materials. Knauf Earthwool is available in R-value ranges comparable to Bradford Gold and is distributed nationally through trade supply channels. Confirm the current R-value range, product width, and NCC compliance from the current Knauf Earthwool TDS before specifying.
Technical Properties
- Glasswool mineral wool batt — formaldehyde-free ECOSE Technology binder
- Available in comparable R-value range to Bradford Gold — confirm current range from Knauf TDS
- Ceiling-level and rafter-level installation in pitched roofs
Limitations
- Confirm current Australian availability, R-value range, and product dimensions from Knauf Insulation before specifying
- Same installation constraints as Bradford Gold — cannot be installed without compression within insufficient rafter or joist depth
- Not a rigid board — same limitations apply as Bradford Gold for under-tile rigid installation
PROCUREMENT SOURCES
Confirm suitability with the current manufacturer TDS before specifying or applying.
System Description
ROCKWOOL stone mineral wool products are manufactured from basalt rock and recycled slag, spun into a fibrous wool form. Unlike glasswool (which is made from recycled glass), ROCKWOOL is a stone-based product with a higher melting point — it is classified as non-combustible and can withstand temperatures significantly higher than glasswool before igniting. This non-combustible classification is the primary differentiator that makes ROCKWOOL the preferred mineral wool product in applications where fire performance is a design requirement or NCC compliance requirement for the roof assembly. ROCKWOOL is also higher density than standard glasswool batts — higher density mineral wool has better acoustic performance and dimensional stability, and semi-rigid ROCKWOOL slabs can be used in between-rafter applications where a slab that holds its shape without full rigid board performance is suitable. ROCKWOOL is vapour-permeable — moisture vapour passes through the insulation, which is important in sarking assemblies where vapour management is a design consideration. Confirm the specific ROCKWOOL product range (Flexi, RockSlab, or other), R-value, NCC fire performance compliance, and current Australian availability from ROCKWOOL before specifying.
Technical Properties
- Stone mineral wool — manufactured from basalt rock and recycled slag — non-combustible
- Higher melting point than glasswool — classified as non-combustible under AS 1530.1
- Higher density than standard glasswool — better acoustic performance and dimensional stability
Limitations
- Higher cost per m² than standard glasswool batts — specify where non-combustible or acoustic performance justifies the cost premium
- Not a rigid board — ROCKWOOL slabs have limited rigidity compared to PIR or phenolic foam boards — they will not span between rafters without support in the same way as a rigid board
- Confirm current ROCKWOOL product range, R-value, NCC fire compliance, and Australian distribution from ROCKWOOL before specifying — product range includes multiple formats (Flexi, RockSlab, etc.)
PROCUREMENT SOURCES
Confirm suitability with the current manufacturer TDS before specifying or applying.
System Comparison
Side-by-side comparison of mineral wool insulation products. Confirm R-value, NCC climate zone requirements, and vapour management with building certifier before specifying.
| Product | Brand | Wool type | Non-combustible | Vapour permeable | R-value range | Density | Binder |
|---|---|---|---|---|---|---|---|
| Bradford Gold | Bradford | Glasswool | No | Yes | R2.5 / R3.5 / R4.0 / R6.0 | Standard | Standard glasswool binder |
| Knauf Earthwool | Knauf | Glasswool | No | Yes | Confirm TDS | Standard | Formaldehyde-free ECOSE |
| ROCKWOOL | ROCKWOOL | Stone wool (basalt) | Yes | Yes | Confirm TDS | Higher than glasswool | N/A — stone fibre |
Do not confuse mineral wool insulation with:
- PIR rigid insulation board (Kingspan Kooltherm K107, Recticel Eurothane GP) — a rigid foam board that achieves a much higher R-value per mm than glasswool or stone wool — different material, much higher cost, rigid format — listed on the Sarking — PIR page
- Reflective foil sarking (Bradford Anticon, Sisalation 475) — a thin flexible multi-layer foil installed under tiles as a secondary weather barrier — provides radiant heat benefit but does not provide significant resistive thermal insulation in the same way as mineral wool batts — listed on the Sarking — foil page
- Spray polyurethane foam (SPF) — two-component expanding foam applied by spray in the roof space — not a batt product and not a standard specification for pitched tiled roof insulation
- Loose-fill insulation (cellulose, loose glasswool) — blown-in loose insulation for attic floor (ceiling level) — a different installation method from batt insulation — not the same product as Bradford Gold or Knauf Earthwool batts
Disclaimer
Confirm R-value, NCC climate zone requirements and vapour management with building certifier before specifying. Final product selection must be confirmed against the current manufacturer technical data sheet, NCC climate zone requirements, and fire rating requirements for the roof assembly. Do not rely on this reference as a substitute for professional engineering or building certifier advice.