When to Choose Non-Combustible Insulation
A1/A2 Fire-Rated Mineral Wool Selection Guide
Non-combustible insulation (A1/A2 fire rating) is required in fire-critical areas and high-temperature applications. This guide explains when mineral wool is necessary and when elastomeric insulation is acceptable.
What is Non-Combustible Insulation?
Non-combustible insulation has an A1 or A2 fire rating under BS EN 13501-1:
- A1: Completely non-combustible (stone wool, glass wool)
- A2: Limited combustibility (mineral wool like K-Rock)
Material: Mineral wool (stone wool or rock wool) | Temperature range: -40°C to +250°C
When Non-Combustible is REQUIRED
- Fire-critical plant rooms — Building Regulations Part B requires non-combustible materials: use K-Rock mineral wool with protective cladding
- Commercial risers (multi-storey buildings) — Vertical pipe shafts in buildings over 18m: A1/A2 rated mineral wool
- Escape routes & corridors — Must not contribute to fire spread: non-combustible mineral wool only
- High-temperature steam (>105°C) — Elastomeric rated to 105°C max: use mineral wool rated to 250°C
- Fire-rated compartments — Areas with 30/60/90 minute fire rating: A1/A2 rated insulation
When Elastomeric is ACCEPTABLE
- Domestic installations (residential hot water, heating, home heat pumps)
- Low-rise commercial buildings under 18m
- Chilled water & refrigeration where condensation control is priority
- Standard HVAC heating/cooling in non-fire-critical areas below 105°C
Decision Matrix
| Application | Fire Requirement | Temperature | Material |
|---|---|---|---|
| Domestic hot water | Class O/1 | 60–80°C | Elastomeric or PE |
| Commercial chilled water | Class O/1 (if allowed) | 6–12°C | Elastomeric (ST/SK) |
| Fire-critical plant room | A1/A2 | Any | Mineral wool (K-Rock) |
| Commercial risers | A1/A2 | Any | Mineral wool |
| High-temp steam | A1/A2 | >105°C | Mineral wool |
| Escape routes | A1/A2 | Any | Mineral wool |
| HVAC (non-critical) | Class O/1 | 40–105°C | Elastomeric |
Mineral Wool Installation Requirements
- Requires protective cladding — aluminium (most common), PVC (indoor), or stainless steel (high-temp/corrosive)
- Vapour barrier for cold pipes — mineral wool is NOT closed-cell; apply external vapour barrier and seal all joints vapour-tight
- Pre-formed sections — slower installation than elastomeric, requires pre-formed elbows and fittings
Compliance & Documentation
You will need: fire test certificates (BS EN 13501-1), product data sheets (fire rating, thermal performance), installation records, and Building Control approval.
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