Part B Explained: Fire Protection Standards for Every Build

What is Building Regulations Part B?

Approved Document B is the UK’s core guidance on fire safety in buildings. It supports compliance with the Building Regulations 2010 and has two volumes, split by building type. Volume 1 deals with houses and flats. Volume 2 covers commercial buildings, schools, hospitals, hotels, and other non-domestic spaces.

Its purpose is to make sure buildings are designed to slow the spread of fire, allow people to escape quickly, and give fire crews what they need to respond.

Unlike planning permission, which governs how a building looks and fits within its surroundings, Part B is part of Building Regulations approval—an entirely separate process that assesses how a building functions and protects people.

You can find detailed technical guidance in the latest version of Approved Document B.

What buildings does Part B apply to?

Part B applies to nearly all types of buildings, including:

• New residential homes and apartment blocks
• Conversions of offices into flats under Class MA or similar
• Commercial buildings such as shops, restaurants and warehouses
• Public-use buildings such as schools, medical facilities, and hotels
• High-rise residential blocks undergoing refurbishment or extensions

It’s also relevant in smaller projects—such as loft conversions or ground-floor extensions—where they impact escape routes, staircases, or compartmentation.

Fire safety should never be an afterthought. Whether you’re drawing up floorplans or applying for planning permission, Part B needs to be built into the design from day one.

What does Approved Document B cover?

Part B focuses on five key fire safety goals. Each section is designed to limit the danger from fire and smoke at every stage—from detection and escape to structural resistance and firefighter access.

Means of warning and escape (B1)
All buildings must have systems in place to detect fires and alert occupants. This can be as simple as smoke alarms in a home or a networked detection system with emergency lighting and signage in a hotel. Escape routes must be clearly defined, unobstructed, and suitable for the people using them.

Internal fire spread – linings (B2)
This section limits the use of materials that help fire spread. It applies to surface finishes on walls, ceilings and linings. Materials must resist ignition and reduce flame spread, especially in areas like corridors, stairwells and common entrances.

Internal fire spread – structure (B3)
To prevent buildings from collapsing during a fire, Part B sets rules for fire-resisting walls, floors and supports. It also includes measures to contain fire within a specific part of a building, using fire doors, firestopping and cavity barriers.

External fire spread (B4)
This section is especially relevant for developers of terraced housing, flats and commercial buildings in dense areas. It controls how easily fire can travel between buildings via cladding, roofs and external finishes.

Access and facilities for fire services (B5)
Buildings must allow fire crews to reach the source of the fire and carry out rescues. This includes suitable access for fire engines, turning circles, dry risers, fire lifts, and clear internal layouts.

You can explore how these rules are interpreted in commercial developments in this Part B guide for surveyors by ICELABZ.

Understanding the key sections of Part B

Part B is a technical document, but its structure helps make it usable. Volume 1 covers single-family homes and low-rise blocks. Volume 2 deals with larger or more complex buildings and includes more in-depth requirements for things like:

• • Atriums and open-plan layouts
  • Basement access
  • Fire-resisting lift lobbies
  • Smoke ventilation in corridors

• High-rise cladding systems
• Sprinkler systems and compartment floors

The 2022 updates to Approved Document B responded to findings from Grenfell Tower and the Building a Safer Future programme. These updates placed greater emphasis on evacuation lifts, fire doors, and combustible materials on external walls.

Sweco also explains how fire engineers interpret and apply Part B within performance-based design frameworks, especially in mixed-use and large-scale developments. You can read more in their guide on fire engineering and Approved Document B.

What is Regulation 38 and why is it important?

Regulation 38 is often overlooked, but it’s a key part of fire safety compliance. It requires that all relevant fire safety information is passed to the building’s owner at completion.

This includes:

• Fire strategies
• Evacuation plans
• As-built drawings with fire compartments marked
• System specifications and manuals (alarms, sprinklers, doors)

This information is critical for ongoing safety and management of the building. Without it, building control approval can be delayed—or rejected entirely.

How Part B links to other building regulations

Part B frequently overlaps with other sections of the Building Regulations. For example:

• Part K, which focuses on protection from falling, must be considered in stair design. A staircase might meet fall protection standards under Part K but still fail under Part B if it’s not wide enough for escape.
• Part M, which sets accessibility rules, affects the width and gradient of escape routes. A wheelchair-accessible path under Part M may also be a designated evacuation route under Part B.
• Part L, which covers thermal efficiency, often involves insulation and cladding choices that must also meet fire safety standards under Part B.

When working across multiple parts of the Building Regulations, it’s essential to have a coordinated design strategy. That’s where our team at WindsorPatania comes in.

How WindsorPatania applies Part B to your project

At WindsorPatania, fire safety is embedded in the way we design, review and manage building projects. Whether we’re working on residential schemes, conversions under permitted development, or mixed-use buildings, we design with compliance from the start—not as an afterthought.

We collaborate with fire engineers where needed, interpret and implement the correct version of Approved Document B, and liaise with Building Control throughout the project. Our architectural and project management teams handle everything from concept drawings to site inspections.

If you’re planning a high-rise development, change of use, or multi-occupancy building, working with a practice that understands how Part B fits into the full regulatory framework is essential. Our full range of building regulations content, including Part K, Part M, and planning insights, can be explored on our Building Regulations hub.

Summary: Why fire safety must be considered early

Fire safety isn’t just about meeting a checklist. It shapes the very structure of a building—how people move through it, how it’s compartmented, how it’s accessed in an emergency.

Approved Document B provides the framework. But applying it properly means understanding your building type, site conditions, and future occupants. From early feasibility studies to project completion, WindsorPatania works to make compliance straightforward and effective.

Ignoring Part B early on could lead to costly redesigns, delays in approval, or worse, long-term risks for residents and users.

Book a discovery call

If your project involves residential design, commercial planning, or any building type where fire safety matters, WindsorPatania can support you from concept to sign-off.

Schedule a discovery call today to discuss your project with our architects and compliance experts.