Building Regulations Part B and fire safety glazing

Approved Document B (Fire safety) provides guidance on meeting the fire safety requirements of the Building Regulations in England. It covers means of warning and escape, internal fire spread (linings and structure), external fire spread and access for the fire service. Glazing — including roof lights — enters the picture where glass forms part of a fire-resisting construction, an escape route or a surface with specified reaction to fire characteristics.

This article outlines general principles. Fire strategy is highly project-specific; it does not constitute legal or fire engineering advice.

When fire safety glazing matters for roof lights

In many single-dwelling projects, roof lights are installed in a standard pitched or flat roof that is not itself a fire-separating element. The glazing must still be safety glass under Part K, but it does not need a fire resistance rating (such as EI 30 or EI 60).

Fire-rated glazing becomes relevant when:

• The roof light is set into a fire-resisting roof that forms a compartment boundary (common in flats, commercial buildings and some attached developments).
• The unit is above or adjacent to an protected escape route — for example, a stairwell in a loft conversion or multi-storey dwelling.
• The fire strategy requires smoke ventilation or firefighting access through the roof, which may dictate openable units or specific sizes.
• External fire spread constraints limit unprotected area in the facade or roof plane near a boundary (more common with vertical glazing, but relevant in some terrace and urban layouts).

In these cases, the roof light assembly must be tested or assessed as part of the construction it penetrates. A standard insulated glass unit without fire test evidence cannot be assumed to maintain compartment integrity.

Fire resistance vs reaction to fire

Two distinct performance families apply:

Fire resistance — measured in minutes of integrity and insulation (e.g. 30, 60, 90). The complete element — glass, frame, seals and fixings — is tested as a system to BS EN 13501-2 or equivalent. Fire-resisting roof lights are specialist products with documented test reports linking them to specific kerb and roof build-ups.

Reaction to fire — classified under the Euroclass system (A1, A2-s1,d0, B-s1,d0, etc.) in Approved Document B Volume 2 for non-domestic and common parts of residential buildings. It describes how a material ignites and contributes to fire growth. Roof light frames, kerbs, upstands and sealants may need to meet minimum classifications depending on the location within the building and the surface classification tables.

Loft conversions and escape routes

Loft conversions are a common trigger for Part B scrutiny. If a new storey creates a third floor or the stair no longer meets escape provisions, the design may require a protected stairway, fire doors, mains-powered detection and careful control of combustible materials. A roof light in the stairwell or landing must not compromise the escape route dimensions or fire-resisting enclosure. Glazing in this context is often fire-rated or limited in area according to the Approved Document guidance for the specific layout.

Roof construction and fire spread over the external envelope

Approved Document B also limits external fire spread via the roof and walls. Unprotected areas — openings without fire resistance — are restricted near site boundaries. While this most often affects windows in facades, large roof glazing in sensitive layouts should be reviewed against the unprotected area calculations in the document. Terraced housing, flats and commercial roofs near boundaries need particular attention.

Smoke control and ventilation

Some building types require smoke ventilation from common corridors, basements or large open-plan areas. Part B cross-references smoke control guidance; openable roof lights or dedicated smoke ventilators may form part of the strategy. These are functional requirements distinct from daylighting roof lights, though a single product may serve both purposes if correctly specified and actuated.

Coordination with the design team

Fire safety is not resolved at product selection alone. The architect, fire engineer and building control body define the strategy before glazing is ordered. If a fire-resisting roof light is required:

1. Confirm the required fire resistance period and the construction it must match.
2. Obtain test evidence or a valid extended application report for the exact build-up.
3. Install with the specified kerb, insulation and fixings used in the test — substitutions invalidate the rating.
4. Document the installation for handover and maintenance records.

Standard made-to-order roof lights for daylighting in single dwellings rarely need fire-rated glazing, but early confirmation avoids costly redesign. Discuss your project with your designer and explore custom roof lights with full specification context.

Vant Glass manufactures premium roof lights and glazing in Aintree, Liverpool — made in Britain, 20-year guarantee, free UK mainland delivery. Explore all products or call 03330 902 592.