Building Regulations

Rooflights and Building Regulations

A rooflight, often called a skylight, is a window installed in a pitched or flat roof to provide more light. Rooflights can reduce CO2 emissions by cutting down on electric lighting.

Installing a new rooflight usually requires Building Regulations approval, though some exemptions exist.

Property owners must ensure compliance with planning rules and building regulations. Non-compliance can result in liabilities, including demolition or restoration.

Always consult with local planning authorities and building control services before starting work to avoid issues.

Planning Permission

Planning permission is often not required for rooflight installation. However, Building Regulations approval is usually needed to ensure the roof's integrity and safety. Factors include the rooflight's weight and thermal performance.

There's no size limit for rooflights from a planning perspective if it fits within a historically reasonable size.

A glazing bar can reduce the perceived size and may be required for traditional properties by local planning authorities.

Always check with local planning officers for specific requirements.

PART B - FIRE SAFETY

Part B of the Approved Document recommends enhanced glazing/fire integrity with a minimum unobstructed openable area for emergency escape or smoke ventilation (BS EN 12101-2).

Rooflights should meet these classifications based on their material. Non-plastic rooflights must adhere to the relevant classification in the table opposite.

Stainless Steel

All Stella rooflights use grade 316L stainless steel, which offers numerous benefits over other materials. Stainless steel is ideal for construction due to its oxidation resistance and strength at high temperatures.

While stainless steel lacks an intrinsic fire rating, its fire resistance is tested under precise conditions (BS476 parts 20, 21, and 22). Stainless steel resists ignition and minimises flame spread. It remains stable and inert under oxidizing conditions found in flames and heat sources.

Research shows stainless steel surpasses carbon steel, aluminum, and galvanized steel in corrosion resistance, durability, and fire prevention. For more details, visit the Gov.uk Planning Portal.

Part F – Means of Ventilation

Part F aims to ensure proper ventilation to limit moisture and pollutants, preventing mold and health hazards. Stella rooflights offer fixed and opening designs. Smaller casements can be manually operated, opening to around 250mm, while larger ones use electric actuators. These actuators are customised and offer various options based on specific customer needs.

Our electric rooflights include accessories for Part F compliance, like sensors and remote controls.

Stella use the most technically advanced ventilation control systems, manufactured in Germany by D+H Mechatronic. Ensuring industry leading performance, safety and energy efficiency.

Please note, Stella Rooflights do not incorporate trickle vents due to their low-profile design.

For more details on Part F, visit the Planning Portal.

Part K – Protection from Falling, Collision & Impact

There is no legal requirement for non-fragile rooflights, unless specified by the customer. A risk assessment should be undertaken to control the risks around any roof work.

Use safety glass, like toughened, laminated, or wired glass, for all overhead applications. Rooflights on accessible but non-traffic roofs should be non-fragile to prevent accidents.

Assess roof access needs during design and specify accordingly, supported by risk assessments.

Stella Rooflights and Part K

Stella conservation rooflights are fragile and not for walk-on use.

Architects, engineers, and manufacturers should discuss large installations early to avoid issues. Ensure large, high-up glazing areas meet BS 5516-2: 2004 standards.

Inner panes must be laminated if rooflights are over 5 meters above floor level or over water. Toughened glass can be used in other cases with a thorough risk assessment.

Avoid leaving these considerations to the builder at the last minute to prevent complications.

Specifying Glass for Rooflights

When specifying rooflight glass, the combination of interlayer and glass panes is crucial for performance. Laminated glass, made of two or more glass sheets bonded with a plastic interlayer, ensures safety as it holds together when broken and can be used overhead.

Annealed glass is weaker than toughened glass and prone to thermal fracture, caused by temperature differences due to shadows or nearby reflective surfaces.

Stella's bespoke rooflights allow customers to specify the right glazing for their projects.

Changes to part L

Part L of the Building Regulations sets out the requirements for the conservation of fuel and power in buildings, including the thermal performance of roof windows and rooflights.

The latest edition of Approved Document L was published in 2026 and is scheduled to come into effect in England on 24 March 2027, subject to transitional arrangements. These changes form part of the Government's ongoing efforts to improve energy efficiency and reduce carbon emissions from buildings.

For architects, specifiers and homeowners, understanding the distinction between roof windows and rooflights, and the different requirements for new and existing buildings, is essential when selecting products that meet the relevant standards.

Natural Daylight

Rooflights provide bright, natural light, reducing the need for artificial lighting. Natural daylight is free and unlimited, lowering CO₂ emissions from reduced energy use.

Buildings without rooflights can have over 50% higher CO₂ emissions. An optimal rooflight area is 15% or more of the floor area.

The thermal performance requirements for roof windows and rooflights vary depending on the type of building and whether the work involves a new build, extension or renovation.

For existing dwellings in England, the applicable limiting U-values are generally 1.4 W/m²K for roof windows and 2.2 W/m²K for rooflights. Different performance standards and notional specifications apply to new-build residential and non-domestic projects.

When assessing compliance, it is important to consider the thermal performance of the complete roof window or rooflight, rather than the glazing alone.

Rooflights and U-Values

There are certain exemptions for listed buildings and properties within designated conservation areas, and we would always recommend seeking guidance from your local authority regarding any requirements that specifically relate to your project.

The thermal performance of a rooflight can vary depending on its design, specification and the angle at which it is installed. U-values may also be reported at different inclinations in accordance with the relevant calculation and testing methodology. It is therefore important to ensure that the U-value being quoted is appropriate for the intended installation and roof pitch, rather than simply comparing headline figures.

Other factors can also affect thermal performance. Manufacturers will often test or calculate the performance of a particular product configuration, and changes to the size, glazing specification, opening mechanism or the inclusion of features such as genuine glazing bars can result in a different whole-product U-value.

For this reason, U-values should always be considered in the context of the specific rooflight being specified. Stella Rooflight can provide thermal performance information for the relevant product configuration and advise on the most appropriate specification for your project.

For more information on rooflights and U-values, read our blog.

Performance Testing

Minimising uncontrolled air leakage is crucial for energy efficiency, often assessed through a weather performance test.

Part L of Building Regulations mandates standards for air permeability, water-tightness, and wind resistance in rooflights. Air permeability, rated from Class 1 to Class 4 (highest), measures draftiness.

Stella Rooflights achieve the highest ratings for Air Permeability and Wind Resistance.

Listed Buildings, Rooflights & Building Consent

For listed buildings, significant internal or external work requires consent. Homes in conservation areas or areas of outstanding natural beauty may have additional restrictions; consult your local authority for guidance.

Navigating Building Regulations can be complex. Seek advice from a qualified professional to ensure compliance.

Stella offers bespoke rooflights, tailored to your project's needs. We are available to discuss requirements and provide guidance on framing materials, glass, thermal performance, and safety.

For more information, email info@stellarooflight.co.uk.