Part B Fire Resistance Ratings Reference
Fire resistance period requirements by building type and element, referencing Approved Document B: Volume 1 - Dwellings (2019 edition incorporating 2020 amendments) and Volume 2 - Buildings other than dwellings.
Minimum Fire Resistance Periods — Dwellings (AD-B Vol 1, Table B3)
The fire resistance period depends on the top storey height of the building measured from ground level to the floor of the top storey.
| Top Storey Height | Typical Storeys | Fire Resistance Period |
|---|---|---|
| Not more than 5 m | Up to 2 storeys | 30 minutes |
| More than 5 m, not more than 18 m | 3 to 6 storeys | 60 minutes |
| More than 18 m, not more than 30 m | 7 to 10 storeys | 90 minutes |
| More than 30 m | 11+ storeys | 120 minutes |
Fire Resistance by Element — Dwellings (AD-B Vol 1, Tables A1 & A2)
| Element | 30-min Building | 60-min Building | 90-min Building | 120-min Building |
|---|---|---|---|---|
| Structural elements (beams, columns) | R 30 | R 60 | R 90 | R 120 |
| Loadbearing walls (not compartment) | R 30 | R 60 | R 90 | R 120 |
| Compartment walls | REI 30 | REI 60 | REI 90 | REI 120 |
| Compartment floors | REI 30 | REI 60 | REI 90 | REI 120 |
| Walls enclosing protected stairway | REI 30 | REI 60 | REI 60 | REI 120 |
| Fire doors to protected stairway | FD30S | FD30S | FD60S | FD60S |
| External walls (within 1 m of boundary) | REI 30 | REI 60 | REI 90 | REI 120 |
Fire Door Ratings (AD-B Appendix B, Table B1)
| Location | Minimum Rating |
|---|---|
| Flat entrance doors (blocks of flats) | FD30S |
| Door to protected stairway (dwelling) | FD20 |
| Door between garage and dwelling | FD30S (with smoke seals) |
| Cupboard enclosing gas meter | FD30 |
| Door to protected corridor (flats) | FD30S |
| Door in 60-minute compartment wall | FD60S |
Scotland & Northern Ireland
Scotland uses the Building (Scotland) Regulations Technical Handbook Section 2 (Fire). Fire resistance requirements are similar but classifications differ (e.g. "short" and "long" fire resistance durations). Northern Ireland follows Technical Booklet E which aligns closely with AD-B but may have different edition dates. Always check the relevant jurisdiction.
Related Calculators
Use the Loadbearing Wall Calculator for structural assessments, or the Fire Stopping Calculator for fire compartmentation.
Always check the latest edition of Approved Documents on the Planning Portal (planningportal.co.uk) as regulations are updated periodically.
How We Calculate This
Frequently Asked Questions
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Last updated: April 2026
All calculations are estimates. Verify with your supplier.