When designing or renovating a building, safety is the highest priority. Internal fire rated windows are a critical component of a building’s overall fire strategy, offering much more than just a view or a source of natural light. They are life-saving barriers designed to contain a fire, providing precious time for occupants to evacuate safely. This fire rated windows expert guide explains the essential information a buyer would need to consider when looking into internal fire rated windows.
What Are Internal Fire Rated Windows?
Internal fire rated windows are specially constructed window systems designed to resist fire for a specified period. Unlike standard windows, which would quickly shatter under the intense heat of a blaze, these windows maintain their integrity. Fire retardant windows prevent the passage of fire and smoke from one part of a building to another. Their primary role is to support a building’s compartmentalisation strategy, which involves dividing the building into smaller, fire-contained sections to slow the spread of a fire.
Understanding Fire Ratings and Classifications
Understanding the terminology used for fire ratings is crucial for selecting the correct product for your project. These ratings are not just numbers and letters; they are precise measurements of performance under extreme conditions, confirmed through rigorous testing.
Fire Resistance Periods
The most prominent feature of a fire rated window is its time rating. This is typically given in minutes, such as 30, 60, 90 or 120 minutes. The rating indicates the minimum length of time the window assembly can withstand a fire. For example, a 60 minute fire rated window is certified to maintain its performance for at least an hour. Aluminium Fire Systems provides a range of options including 30 minute fire rated windows and solutions up to 120 minute fire rated windows.
Integrity and Insulation Classifications
Beyond the time rating, performance is defined by classifications, primarily concerning integrity and insulation.
- E – Integrity: This is the most basic classification. It measures the ability of the window to prevent the passage of flames and hot gases. The window itself will still get extremely hot and can radiate significant heat.
- EW – Integrity and Radiation Control: This class offers a middle ground. The window maintains its integrity (E) and also provides some reduction in the amount of radiant heat passing through the glass.
- EI – Integrity and Insulation: This is the highest level of protection. The window not only stops flames and hot gases (Integrity) but also significantly blocks the transfer of heat to the non fire side (Insulation). This is vital for protecting escape routes and designated safe areas, as it prevents combustible materials on the safe side from igniting due to radiant heat. At Aluminium Fire Systems, we specialise in EI rated systems like the EI60 fire rating to provide the highest level of safety.
View our article for more information:Types of Fire Safety Glass: E vs EI
The Anatomy of a Fire Rated Window
A fire rated window is a complete system where every component is engineered to work together. The performance of the whole assembly is only as strong as its weakest link.
Fire Rated Glass
The type of glass is fundamental to a window’s fire performance. There are several types of fire rated glass available.
- Wire glass, often seen in older buildings, has a wire mesh embedded within it. The wire holds the glass in place if it cracks under heat.
- Ceramic glass has a very high resistance to heat and thermal shock, allowing it to remain clear and intact for longer periods.
- The most advanced option is intumescent laminated glass. This glass has multiple layers, including a clear intumescent layer that reacts to heat. When a fire breaks out, this layer expands and turns into a solid, opaque barrier that blocks flames and provides full heat insulation, achieving an EI rating.
Fire Rated Frames
The frame is just as important as the glass. A frame that warps, melts or fails will compromise the entire system, no matter how effective the glazing is. Frames must be tested alongside the glass to achieve certification.
While steel has traditionally been used, modern fire rated aluminium windows offer significant advantages. Aluminium provides a much slimmer and more aesthetically pleasing profile without sacrificing strength or performance. Systems such as the MB-78EI use specially designed aluminium extrusions with fire resistant inserts, ensuring they provide robust integrity and insulation.
Navigating UK Building Regulations and Standards
Specifying fire rated windows means complying with UK Building Regulations, specifically Approved Document B. These regulations dictate where fire resisting construction is required and what performance levels are necessary. Products must be tested to British Standards (BS) or the superseding European Standards (EN) to prove their performance. A reputable supplier will always provide a full compliance pack with every project, containing the necessary test evidence and certifications for building control approval.
Compliance in Action:
We recently supported a contractor on a high-rise residential refurbishment in Wolverhampton. When Building Control questioned whether the slim profiles of our aluminium windows could meet a 60-minute fire rating, our technical team stepped in. By sharing our expertise and specific test evidence for the MB-78EI system during the pre-order phase, we gave the inspectors the confidence they needed. This early-stage clarity ensured the project met the EI60 standard perfectly and allowed the order to proceed without delays (such as redesigns), with the full compliance pack delivered alongside the finished goods.
Common Applications for Fire Rated Windows
Internal fire rated windows are essential in many commercial and residential buildings. They are typically required in specific locations to ensure escape routes are protected. Common applications include:
- Protected Corridors: To separate corridors from adjacent rooms and offices, allowing them to serve as safe passages.
- Stairwells and Lobbies: To create a protected zone that prevents fire and smoke from blocking vertical escape routes.
- High Risk Areas: To segregate areas like kitchens or plant rooms from the rest of the building.
- Internal Walls: As part of fire rated glass partitions that divide large open plan spaces without losing natural light.
Maintenance and Lifecycle of Fire Rated Windows
While fire rated windows are designed for durability, their performance in an emergency depends on their condition. Unlike standard windows, a small crack or a perished seal in a fire window can be the difference between containment and failure.
- Periodic Inspections: Under the Regulatory Reform (Fire Safety) Order 2005, the ‘Responsible Person’ for a building must ensure that all fire safety equipment, including fire-rated glazing, is maintained in efficient working order. Experts recommend at least an annual inspection to check for chips in the glass or damage to the frame.
- Seal Integrity: The intumescent seals between the glass and the frame are critical. If these seals are painted over, removed, or show signs of peeling, the window’s fire rating may be voided.
Documentation: Current UK guidance (including DLUHC Circular 2025-1) notes the importance of the ‘Golden Thread’ of information. Owners should maintain a log of all inspections and certifications for every fire-rated opening in the building.
Sustainability: Why Aluminium is the Architect’s Choice
In modern construction, sustainability is just as important as safety. Aluminium offers a superior environmental profile compared to many traditional materials.
- Infinite Recyclability: Recycling aluminium requires only 5% of the energy used to produce primary aluminium, and it can be recycled repeatedly without losing its properties.
- Lower Embodied Carbon: By partnering with industry leaders like Aluprof, we offer systems that prioritise low-carbon production. Aluprof provides ultra-low carbon billets and many of their profiles carry Environmental Product Declarations (EPDs), helping architects meet BREEAM and LEED requirements.
- Longevity: Studies show that aluminium systems can have a service life of 40–50 years, ensuring that internal fire partitions remain structural and aesthetically pleasing for decades.
Partitions
Fire rated glass partitions divide spaces in open-plan offices, schools and hospitals without blocking natural light. They create specific zones like meeting rooms while ensuring that if a fire starts, it stays contained within the area of origin. This capability extends to the building envelope, allowing large glass facades and curtain walls to meet safety regulations without compromising the architectural design.
Why Choose Aluminium Fire Systems?
As one of the UK’s leading specialists in manufacturing and supplying fire rated aluminium systems, we are dedicated to providing solutions that are safe, compliant and aesthetically pleasing.
- UK Manufacturing and Fast Delivery: All our products are manufactured in the UK. Our streamlined processes and effective project management enable us to offer fast lead times and on time nationwide delivery, ensuring we meet your project deadlines.
- Assured Compliance: We take compliance seriously. Our team stays up to date with the latest standards and every project is supplied with a full compliance pack. This gives you peace of mind that our products meet all relevant regulations.
- Competitive Pricing: By buying direct from the manufacturer, we eliminate middleman costs. We optimise our production processes to deliver cost effective solutions without ever compromising on the quality and performance of our products.
- Exceptional Quality: We use high quality profiles from trusted suppliers like Aluprof, who have over 70 years of experience. This ensures every window, door and partition system we produce is built to last and perform when it matters most.
Internal Fire Rated Windows Expert Guide Frequently Asked Questions
What are the requirements for a window in a fire rated wall?
The window assembly must match the fire resistance of the wall itself. For example, if a wall is rated for 60 minutes, the window must also provide a minimum of 60 minutes of protection. According to UK Building Regulations (Approved Document B), any opening in a fire-separating element must be protected so that the fire resistance of the element is not impaired.
What are the requirements for fire rated glass?
Fire rated glass must be tested as part of a complete system. In the UK, it must comply with BS EN 1364-1:2015 for non-loadbearing elements. The glass must be clearly marked with its rating and the manufacturer’s name. It must also meet safety standards for impact, such as BS EN 12600 (Class 1 or 2).
Do I need a FD30 or FD30S?
The “FD” (Fire Door) terminology refers specifically to door sets. An FD30 rating means the door provides 30 minutes of fire integrity, while an FD30S rating means it provides 30 minutes of fire integrity PLUS protection against cold smoke. For windows, you will look for “E” (Integrity) or “EI” (Integrity and Insulation) ratings.
Where are fire-rated windows required?
Specifically, Approved Document B mandates fire-rated glazing in internal partitions that enclose protected stairways, protected lobbies, and corridors that serve as a means of escape. They are also required when a window is positioned within a certain distance of an external escape route to prevent “fire jump.”
About The Author
Lauren Walker is the Managing Director of Aluminium Fire Systems. With extensive experience in the UK’s fire rated glazing industry, she is committed to promoting the highest standards of fire safety in building design and construction.