Repair Systems — 04
Sarking systems — PIR under-tile insulation board
Technical product reference for PIR and phenolic rigid foam insulation boards for under-tile installation in pitched roof thermal upgrade. Covers Kingspan Kooltherm K107, Recticel Eurothane GP, and Celotex RS5000 — R-value, NCC compliance, thermal bridging, and ventilation requirements.
What are PIR under-tile insulation board systems?
PIR (polyisocyanurate) under-tile insulation board systems are rigid foam boards installed between or below the rafters of a pitched tiled roof to provide high-performance thermal insulation. PIR boards achieve a significantly higher R-value per mm than traditional glasswool or EPS insulation, making them particularly valuable where rafter depth or available roof space limits the insulation thickness that can be installed without modifying the roof structure or tile level. Kingspan Kooltherm K107 (phenolic foam) and Recticel Eurothane GP (PIR) are the primary products in this category.
Product Reference
3 products — 3 brands — PIR under-tile insulation boards — scroll to view all
Kingspan Kooltherm K107 Pitched Roof Board
PIR / phenolic insulation board — under-tile — AS/NZS 4859
System Description
Kingspan Kooltherm K107 is Kingspan's high-performance phenolic rigid foam insulation board specifically designed for pitched roof applications including under-tile and between-rafter insulation. Phenolic foam achieves a significantly higher R-value per mm of thickness than PIR (polyisocyanurate), EPS (expanded polystyrene), or glasswool batts — this makes K107 the preferred product where maximum thermal performance is required within a constrained thickness, such as where the rafter depth limits available insulation space. Both faces are foil-faced for radiant heat reflection. The product is available in Australia through Kingspan's local supply chain. Confirm the specific R-value per 50mm (or per nominated thickness), NCC compliance, and current Australian availability from the Kingspan Australia technical team before specifying K107 on a pitched tiled roof project. Confirm whether the nominated thickness is compatible with the available rafter depth and tile batten clearance on the specific roof.
Technical Properties
- Phenolic rigid foam — highest R-value per mm of common under-tile insulation board products
- Foil-faced both surfaces — reflective radiant heat barrier
- Designed for between-rafter and under-tile application on pitched roofs
Limitations
- Phenolic foam is more expensive per m² than PIR, EPS, or glasswool — confirm cost-benefit against the project's NCC R-value requirement
- Rigid board — must be cut to fit between rafters — requires accurate measurement and a clean cutting method — phenolic foam generates dust during cutting — use appropriate respiratory protection
- Confirm available rafter depth and tile batten clearance before specifying board thickness — if the board is too thick it will not fit within the available space without modifying the batten height
PROCUREMENT SOURCES
Confirm suitability with the current manufacturer TDS before specifying or applying.
Recticel Eurothane GP
PIR insulation board — foil-faced — under-tile — AS/NZS 4859
System Description
Recticel Eurothane GP is a polyisocyanurate (PIR) rigid foam insulation board from Recticel, foil-faced on both sides, used in pitched roof upgrade and thermal improvement applications including under-tile installation between rafters. PIR achieves a higher R-value per mm than EPS or glasswool but is generally lower than phenolic foam (such as Kingspan Kooltherm). Eurothane GP is used where a cost-effective rigid board solution is required for improved thermal performance under a tiled roof, and where the full performance premium of phenolic foam is not required or cannot be justified on cost grounds. Confirm current Recticel Eurothane GP specifications, R-value per nominated thickness, AS/NZS 4859 compliance, NCC climate zone applicability, and Australian distribution availability from Recticel before specifying.
Technical Properties
- PIR (polyisocyanurate) rigid foam — foil-faced both sides
- Higher R-value per mm than EPS or glasswool — lower than phenolic foam
- Suitable for under-tile and between-rafter installation on pitched roofs
Limitations
- Confirm Australian distribution availability and current stock with Recticel before specifying — Recticel is primarily a European manufacturer and Australian availability may be subject to lead times
- Confirm R-value per nominated thickness and NCC compliance from current Recticel Eurothane GP TDS
- Rigid board — same cutting and installation constraints as Kingspan K107 — confirm rafter depth and batten clearance
PROCUREMENT SOURCES
Confirm suitability with the current manufacturer TDS before specifying or applying.
System Description
Celotex RS5000 is a PIR (polyisocyanurate) insulation board from Celotex, a UK-based rigid insulation manufacturer. It is a foil-faced rigid PIR board used in pitched roof upgrade applications including rafter-level insulation. This product is listed as a reference — the owner must confirm whether Celotex RS5000 is currently available through Australian distribution before specifying it on an Australian project. If Australian distribution is confirmed, the RS5000 provides a PIR board alternative to Recticel Eurothane GP in the same application category. If Australian distribution cannot be confirmed, specify Recticel Eurothane GP or Kingspan Kooltherm K107 instead. Do not specify Celotex RS5000 on an Australian project without first confirming current Australian availability, pricing, lead times, and NCC compliance from the Australian distributor.
Technical Properties
- PIR rigid foam — foil-faced both sides
- Pitched roof upgrade and rafter-level insulation application
- Celotex — UK-based rigid insulation manufacturer
Limitations
- TODO — Australian distribution availability must be confirmed before this product is specified on any Australian project
- If Australian distribution cannot be confirmed, use Recticel Eurothane GP or Kingspan Kooltherm K107 instead
- UK product — NCC climate zone compliance must be confirmed with the Australian distributor
PROCUREMENT SOURCES
Confirm suitability with the current manufacturer TDS before specifying or applying.
System Comparison
Side-by-side comparison of PIR under-tile insulation board products. Confirm R-value, NCC climate zone requirements, and Australian supply before specifying.
| Product | Brand | Foam type | R-value per 50mm | Foil-faced | Under-tile use | Australian supply |
|---|---|---|---|---|---|---|
| Kooltherm K107 | Kingspan | Phenolic | Confirm TDS — highest | Yes — both sides | Yes | Yes |
| Eurothane GP | Recticel | PIR | Confirm TDS | Yes — both sides | Yes | Confirm with Recticel |
| RS5000 | Celotex | PIR | Confirm TDS | Yes — both sides | Yes | TODO — confirm distribution |
Do not confuse PIR under-tile insulation boards with:
- Reflective foil sarking (Bradford Anticon, Sisalation 475) — a thin flexible membrane installed under tiles for secondary weather protection and radiant heat benefit — much thinner than PIR board, different primary function, much lower cost — listed on the Sarking — foil page
- Ceiling insulation batts (Bradford Gold, Knauf Earthwool, ROCKWOOL) — installed below the ceiling between ceiling joists, not under tiles at rafter level — these are ceiling batts, not under-tile insulation boards — listed on the Sarking — mineral wool page
- EPS (expanded polystyrene) insulation board — a lower-cost rigid board that achieves a lower R-value per mm than PIR or phenolic foam — not on this page
- Spray foam insulation — two-component polyurethane spray foam applied in the roof space — not a rigid board and not an under-tile product
Disclaimer
Thermal performance claims vary by thickness. Confirm R-value and NCC compliance with manufacturer. Confirm climate zone requirements with building certifier before specifying. Final product selection must be confirmed against the current manufacturer technical data sheet and project specification. Do not rely on this reference as a substitute for professional engineering or building certifier advice.