How is fire resistance period determined?

The minimum fire resistance period is determined by Approved Document B, Table A2, based on the building's purpose group (residential, office, etc.), the height of the topmost floor above ground, and whether the element is in a basement. Periods range from 30 to 120 minutes.

What do REI and EI mean?

R = loadbearing capacity (resistance to collapse), E = integrity (resistance to fire penetration), I = insulation (resistance to heat transfer). Loadbearing elements need REI; non-loadbearing separating elements need EI. The number after (e.g. REI 60) indicates minutes of resistance.

Does building height affect fire resistance?

Yes, significantly. Buildings up to 5m typically need 30 minutes. Buildings 5-18m need 60 minutes. Buildings 18-30m need 90 minutes. Buildings over 30m need 120 minutes. Basements have separate requirements, typically 60-120 minutes depending on depth.

Can sprinklers reduce fire resistance requirements?

In some cases, Approved Document B allows a reduction of up to 30 minutes where a sprinkler system is installed. However, this reduction is not available for all situations. A sprinklered building at 60 minutes may be reduced to 30 minutes, but check specific conditions.

What test standard proves fire resistance?

Fire resistance is demonstrated by testing to BS 476 Parts 20-24 or the European equivalent BS EN 1363/1364/1365/1366. Products must have valid test certificates or assessments. Common fire protection systems include fire-rated plasterboard, intumescent coatings and concrete encasement.

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Fire Resistance Calculator

Determine the minimum fire resistance period for structural elements per Approved Document B. Lookup Table A2 requirements by building height, purpose and element type.

Building Purpose

Purpose group per AD B

Element Type

Structural element to protect

Building Height

Height of topmost floor above ground

Basement?

Basements have separate requirements

Number of Elements

Elements requiring protection

Cost per Element

Fire protection cost per element

How We Calculate This

This calculator looks up the minimum fire resistance period from Approved Document B, Table A2 based on building parameters.

The lookup

Fire resistance = f(building purpose, height, element type, basement)

Up to 5m: 30 mins
5-18m: 60 mins
18-30m: 90 mins
Over 30m: 120 mins
Basements: 60-120 mins

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Last updated: March 2026

All calculations are estimates. Verify with your supplier.