Minimum fire resistance period lookup (Table B2)
Approved Document B sets the minimum period of fire resistance for elements of structure in Appendix B, Table B2. The period depends on the purpose group, the height of the top storey above ground level or the depth of the basement, and whether the building has a sprinkler system.
Fire resistance is expressed as three separate performance criteria (R for loadbearing capacity, E for integrity and I for insulation), and an element does not need all three. A loadbearing internal wall that is not a compartment wall needs R only; a compartment wall needs REI.
Not permitted without additional measures
Note 2 to Table B2: blocks of flats with a top storey more than 11 m above ground level should be fitted with a sprinkler system throughout, in accordance with Appendix E. Above 11 m there is therefore no non-sprinklered period to read.
Working
| Step | Value |
|---|---|
| Table B2 columnGround or upper storey, top floor up to 30 mADB Table B2 | 21 m high |
| Purpose groupFlats (residential, purpose group 1(a))ADB Table B2 | non-sprinklered column |
Sources
- Approved Document B, Appendix B, Table B2Minimum periods of fire resistance for elements of structure. Printed in full, and identically, in both Volume 1 (page 136) and Volume 2 (page 147).
- Approved Document B, Appendix B, Table B1Specific provisions of the test for fire resistance of elements of structure: which of R, E and I each element needs, and where the period is read from Table B2. Item 23, fire doorsets, routes to Appendix C.
- Approved Document B, Appendix C, Table C1Provisions for fire doorsets. Door periods are set by the position of the doorset, not by a single formula: same as the element for items 1, 2e and 3; half the period with a 30 minute minimum for item 2c and item 2d only, both of them protected shafts; a fixed period for the rest.
- BS EN 13501-2Fire classification from fire resistance tests: R loadbearing capacity, E integrity, I insulation.
- BS 476-20 to -24The former British Standard test methods, still referenced for existing buildings.
This is an engineering aid, not engineering advice. The result above is produced from the inputs you gave and the guidance cited. It does not account for everything a competent fire engineer would consider on a real building, and it is not a substitute for reading the current published standard. Check every number before it goes into a design.
Questions people ask
What fire resistance does a compartment wall need?
The period from Approved Document B Table B2 for the purpose group and height, and all three criteria: loadbearing capacity, integrity and insulation, so REI. A compartment wall that is not loadbearing only needs EI. In a block of flats over 30 m, that is REI 120.
What does REI 60 mean?
60 minutes of loadbearing capacity (R), integrity against the passage of flame and hot gases (E) and insulation limiting temperature rise on the unexposed face (I), tested to BS EN 13501-2. The old British Standard equivalent was expressed as 60 minutes to BS 476 Parts 21 and 22.
Do sprinklers reduce the required fire resistance?
In several cases, yes. Table B2 has separate columns for sprinklered buildings, and the reduction can be a full 30 minutes; for example, an office with a top storey between 18 m and 30 m drops from 90 to 60 minutes. It also unlocks larger compartment sizes. The system has to be designed and maintained to the relevant standard for the life of the building.
What fire rating does a fire door need?
It depends on where the door is. Approved Document B sets door periods in Appendix C, Table C1, by the position of the doorset rather than by a single formula. The default is the same period as the element the door is fitted in: item 2e, the catch-all for doors in compartment walls, reads "same as for the wall in which it is fitted", so a 60 minute compartment wall needs FD60, not FD30. The widely repeated "half the wall's period, 30 minutes minimum" is the rule for exactly two rows, both of them protected shafts: item 2c and item 2d. Several positions are fixed periods instead: FD30S between a flat and a space in common use, FD30S into a protected stairway, FD20S into any other protected corridor. The S suffix is for restricted smoke leakage and applies wherever the door serves an escape route.
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