What Is Part B? — Fire Safety Regulations

Definition

Part B (Approved Document B: Fire Safety) is the section of the Building Regulations for England that sets out requirements for fire safety in and around buildings. It covers means of warning and escape, internal fire spread (linings and structure), external fire spread, and access and facilities for the fire service. Part B is divided into Volume 1 (dwelling houses) and Volume 2 (buildings other than dwellings).

When Is It Used?

Part B applies to all new buildings and most building work including extensions, loft conversions, material alterations, and changes of use. It is particularly critical for loft conversions (which create a new storey), HMO conversions, garage-to-house connections, and any work involving party walls or compartment floors. Fire safety is also reviewed during completion inspections by Building Control.

Key Facts

• Interlinked smoke alarms on every storey are mandatory in all new builds and conversions since June 2022
• Fire doors are rated FD20 (20-minute) or FD30 (30-minute) depending on location
• Party walls between houses must provide 60-minute fire resistance
• Surface spread of flame: Class 0 or Class B-s3,d2 (Euroclass) for walls and ceilings in escape routes
• Fire stopping is required at all penetrations through compartment walls and floors
• Escape windows must have a minimum clear opening of 450 x 450 mm with sill max 1100 mm above floor
• Buildings over 11 metres: combustible cladding materials banned (Regulation 7 amendment)
• Carbon monoxide alarms required in rooms with fixed combustion appliances (except gas cookers)

Related Calculators

Use the Fire-Rated Plasterboard Calculator for fire-resisting constructions, or the Smoke Alarm Calculator for alarm placement. The Fire Door Calculator helps specify the correct fire door ratings.