Fire Resistance Periods and Material Classifications

What This Requirement Covers

Approved Document B specifies minimum fire resistance periods for structural elements, compartment walls and floors, and fire-protecting elements. The fire performance of materials is classified according to European testing standards, which replaced the older British Standard classifications.

Understanding fire resistance and material classification is essential for specifying compliant construction.

Key Requirements

Fire Resistance Periods

Fire resistance is expressed in minutes and has three criteria

1. R (Loadbearing capacity): The time the element can continue to support its load
2. E (Integrity): The time the element can prevent the passage of flames and hot gases
3. I (Insulation): The time the element can limit temperature rise on the unexposed face

Common requirements

1. Separating wall between houses: REI 60 (from both sides)
2. Compartment wall in flats up to 5 m: REI 30
3. Compartment wall in flats 5-18 m: REI 60
4. Compartment wall in flats over 18 m: REI 120
5. Compartment floor in flats over 18 m: REI 60
6. Protected stairway enclosure: REI 30 (up to 18 m) or REI 60 (over 18 m)
7. Structural frame in buildings over 18 m: R 120 (elements in the lowest storey), R 60 (upper storeys)

European Fire Classification (Reaction to Fire)

Materials are classified under BS EN 13501-1 from best to worst

1. A1: Non-combustible (e.g., concrete, steel, stone, glass)
2. A2: Limited combustibility (e.g., plasterboard, mineral wool, some fibre cement)
3. B: Very limited contribution to fire (e.g., some fire-retardant timber treatments, phenolic foam)
4. C: Limited contribution to fire
5. D: Acceptable contribution to fire (e.g., untreated timber)
6. E: Some reaction to fire
7. F: No performance determined

Additional suffixes

1. s1, s2, s3: Smoke production (s1 = low, s3 = high)
2. d0, d1, d2: Flaming droplets (d0 = none, d2 = significant)

Internal Surface Linings

1. Walls and ceilings in circulation spaces: minimum Class C-s3,d2 (or national Class 1 per BS 476: Part 7)
2. Walls and ceilings in rooms: minimum Class D-s3,d2 (or national Class 3)
3. Small rooms under 4 m² may use Class D regardless of location
4. The classification applies to the exposed surface, not the entire construction

Testing Standards

1. BS EN 1364 and BS EN 1365: Fire resistance tests for non-loadbearing and loadbearing elements
2. BS EN 13501-1: Reaction to fire classification
3. BS EN 13501-2: Fire resistance classification from test data
4. BS 476: Part 6 and Part 7: The older British Standard tests still referenced as alternatives
5. BS 8414: Large-scale fire test for external wall systems (used for buildings 11-18 m as an alternative to material classification)

Practical Compliance Tips

1. Always obtain fire test certificates and classification reports for specified materials before construction
2. The fire resistance of an element depends on the complete construction (not just one material); ensure the tested assembly matches the as-built configuration
3. Where a wall or floor is loadbearing, it must satisfy R, E, and I; non-loadbearing elements need only E and I
4. Fire resistance is tested from both sides unless the element is only exposed to fire from one direction
5. Keep all fire test evidence for the building file and Golden Thread (for higher-risk buildings)
6. When substituting materials on site, check that the replacement achieves the same or better classification
7. Use the manufacturer's fire resistance assessment or design guide to confirm that the proposed construction meets the required period