Fire-Rated Skylights for Pitched Roofs: UK Building Regulations

While standard fire-rated options exist, they can be limited or difficult to specify. This article explores the availability of fire-rated skylights, viable non-combustible alternatives, and best practices for ensuring compliance with UK building regulations, specifically Approved Document B.

Fire-Rated Skylights: Availability and Limitations

Fire-rated skylights are designed to resist fire penetration for defined periods, maintaining integrity (E) and insulation (I) to limit flame spread and heat transmission. These are typically classified as EI30, EI60, or EI90, representing 30, 60, or 90 minutes of fire resistance, respectively.

• E (Integrity): The ability of the skylight to prevent the passage of flames and hot gasses.
• I (Insulation): The ability of the skylight to limit the temperature rise on the non-fire side (generally to no more than 140°C average and 180°C at any single point).
• EW (Integrity and Radiation Reduction): This is the ability of a test component to resist fire exposure on one side only, so as to reduce the probability of the transmission of fire.

Fire-rated glass is a requirement on any rooflight in an area that is part of a fire escape, in line with current building regulations. At Sunsquare, our fire-rated skylights feature a subframe below the skylight, completely out of sight, ensuring aesthetic appeal while meeting all building control requirements. We currently offer either 30 or 60-minute ratings (EI30 or EI60).

Although essential in areas such as escape routes or compartmentation zones, finding suitable pitched-roof products can be complex. Despite available offerings, architects often find a gap when specifying skylights for steeper pitched roofs, prompting exploration of non-standard solutions.

Non-Combustible Skylights: A Practical Alternative

Non-combustible skylights, typically glass-based, represent an effective alternative, especially when combined with complementary fire-resistant materials. Glass skylights meet Class A1 classification under BS EN 13501-1, indicating they do not contribute to fire spread and thus provide superior performance regarding external fire safety. BS EN 13501-1 also includes additional classifications:

• s: Smoke production (s1 being the best, s3 the worst).
• d: Flaming droplets/particles (d0 being the best, d2 the worst).

The viability of non-combustible skylights is enhanced significantly by pairing them with fire-retardant materials for the timber upstand. Such an assembly ensures that the entire rooflight installation resists ignition, greatly reducing potential fire risks.

Recommended Assembly

• Glass Skylight (Non-Combustible, Class A1 under BS EN 13501-1)
• Timber Upstand: Class B-s1, d0 fire-retardant plywood (or similar, meeting the specified BS EN 13501-1 classification). Consider the Sunsquare Upstand for a precision-engineered, energy-efficient solution.
• Insulation: Non-combustible mineral wool (A1 rated).

This combination not only ensures regulatory compliance but also aligns closely with the aesthetic considerations essential for conservation projects. A fully weathered upstand must be 150mm above the roof surface. The Sunsquare Upstand, developed in partnership with Warren Insulation, offers a U-value of 0.58 and a zero percent chance of dew formation, making it a superior choice.

Compliance with UK Building Regulations

Adhering strictly to Approved Document B of the UK Building Regulations is vital. Approved Document B provides clear directives regarding fire safety, notably for rooflights. It is split into two volumes:

• Volume 1: Dwellings (including blocks of flats). Approved Document B Volume 1
• Volume 2: Buildings other than dwellings. Approved Document B Volume 2

This article primarily focuses on Volume 2 (non-dwellings) but also touches on relevant aspects of Volume 1 (dwellings, escape routes) when it comes to critical areas. Key sections of Approved Document B include:

• B1: Means of warning and escape.
• B2: Internal fire spread (linings).
• B3: Internal fire spread (structure).
• B4: External fire spread.
• B5: Access and facilities for the fire service.

Of particular relevance:

• External Fire Spread: Glass skylights (Class A1) comply inherently due to non-combustibility (Section B4).
• Internal Fire Resistance: Fire-rated skylights are necessary above critical areas such as escape routes, stairwells, and compartmentation boundaries (Section B3).

Furthermore, the transition away from BS 476 towards BS EN 13501 classifications is ongoing within Approved Document B. Notably, as of March 2, 2025, classifications according to BS EN 13501 became mandatory for reaction to fire and roofs, replacing the previous BS 476 references for these specific aspects.

Conservation Projects: Balancing Safety and Aesthetics

Conservation projects present unique challenges due to their stringent aesthetic and regulatory requirements. Skylight installations must harmonise with historical features. Planning permission is likely required for skylight installations in conservation areas or on listed buildings, often because Article 4 Directions remove standard permitted development rights in these locations.

Non-combustible glass skylights, which inherently blend discreetly within traditional rooflines, become particularly advantageous here. When integrated carefully with fire-retardant upstands, they meet fire safety standards without compromising architectural integrity.

Practical Considerations for Architects

When specifying skylights for pitched roofs, particularly in heritage projects, consider the following:

1. Assess the Building Context: Determine if the skylight location necessitates fire-rated or non-combustible solutions based on proximity to escape routes and boundary conditions.
2. Material Selection: Opt for glass-based skylights (Class A1 non-combustible) where fire-rated alternatives are limited or unsuitable.
3. Assembly Integration: Combine glass skylights with Class B-s1, d0 fire-retardant plywood and A1-rated mineral wool insulation to maximise fire safety performance. Consider the Sunsquare Upstand for optimal performance.
4. Consult Regulators and Planners: Always engage building control authorities for fire safety compliance. Regarding planning permission, while skylight installations may fall under permitted development rights outside conservation areas (subject to specific size, protrusion, and location limits), it’s crucial to verify with the local planning authority, especially if Article 4 Directions apply or the building is listed.
5. Check Component Ratings: Verify the specific fire ratings (EI and s/d classifications) of all components used in the skylight assembly.

Comparative Table: Fire-Rated vs. Non-Combustible Skylights

Why Real-Life Testing Matters – The Sunsquare Approach

Some manufacturers rely on engineered assessments to determine fire ratings. This involves computer simulations. At Sunsquare, we believe fire safety can’t be left to chance. That’s why we invest in physical, third-party testing, ensuring our products meet the most stringent standards through real-life assessments. Our skylights are independently certified by CERTIFIRE, achieving EI30 or EI60 ratings for both integrity and insulation. This provides tangible proof of compliance and performance.

Conclusion

While fire-rated skylights are available and necessary for specific applications, non-combustible glass skylights, when properly integrated with fire-resistant construction elements (like Class B-s1, d0 fire-retardant plywood and A1 mineral wool insulation), present an effective and aesthetically pleasing alternative.

For pitched roofs in conservation settings, this approach offers architects a reliable method to balance rigorous fire safety standards with critical preservation objectives, ensuring both regulatory compliance (Approved Document B) and historical integrity.

Choosing Sunsquare products ensures you get skylights proven to protect lives and property.

For architects seeking tailored solutions and expert advice on fire-rated and non-combustible skylights, contact Sunsquare today. Our team is ready to assist with your specific project needs. Get in touch or call us at 01922 714087. Explore our range of fire-rated skylights and discover the Sunsquare difference.