Fire rated internal doors: FD30 requirements, glazing and compliant specification 

• 30 April 2026
• News

Fire rated internal doors are a core part of passive fire protection in commercial buildings and multi-occupancy residential schemes. For architects, contractors and developers, FD30 specification is often the baseline requirement, but performance depends on the integrity of the complete tested system. 

Within steel door systems, Crittall Windows provides Innervision fire rated internal doors designed for controlled fire resistance, glazed performance and compliance with UK building regulations. The focus is around the full assembly and how it performs in fire conditions. 

Crittall also offers cold formed steel systems in other applications, so performance and fire rating should always be checked against the specific tested assembly. Fire rated cold form systems offer both integrity and insulation with performance classifications of up to EI120. 

What FD30 means for internal fire doors

FD30 refers to fire resistance of at least 30 minutes when tested as a complete doorset. This includes the door leaf, door frames, hinges, glazing, seals and ironmongery. The system must maintain structural integrity and restrict fire spread for the duration of the test. 

In practical terms, FD30 fire doors are designed to hold back flames and limit the spread of fire long enough to support escape and emergency response. During the event of a fire, this separation is what protects escape routes and reduces exposure to high temperatures and smoke. 

Regulatory context and legal requirement

Fire doors are a legal requirement in many buildings under UK fire safety regulations. The Regulatory Reform (Fire Safety) Order 2005 places responsibility on the appointed responsible person to manage fire safety risk, including the correct specification and maintenance of internal fire doors. 

The Fire Safety Act 2021 extends responsibility in residential blocks, particularly buildings with multiple floors. Building Regulations Approved Document B sets out performance standards for fire resistance, compartmentation and escape routes. 

For commercial buildings, fire rated internal doors are commonly required in corridors, stair enclosures and protected lobbies. In residential schemes, they are used in communal areas, flat entrances and shared escape routes. 

Why the complete doorset matters

Compliance is based on tested assemblies, not individual components. A certified FD30 system must include: 

• Door leaf tested as part of a full assembly  

• Door frames specified within the tested configuration  

• Intumescent seals and smoke seals  

• Glazing systems where applicable  

• Hinges, locks and door closers included in certification scope  

Substituting any of these elements without checking certification can compromise fire resistance. This is a common issue where standard internal doors are mistakenly upgraded with partial fire protection components without full system validation. 

Proper installation is equally important. Poor fitting, incorrect gaps or misaligned frames can reduce performance under fire conditions. Building control officers and fire risk assessors will often check installation quality as part of compliance review. 

Steel fire doors and glazed performance

Steel fire doors are widely used where durability, slim sightlines and consistent performance are required. In Crittall systems, steel construction supports structural stability at high temperatures, helping maintain fire resistance under stress. 

Glazing is a key feature in many internal fire doors, particularly in commercial buildings where light transfer and visibility are required. Glass panels used in fire rated systems are tested fire resistant units designed to withstand heat while maintaining integrity. 

Within Crittall fire rated internal doors, specialist fire resistant glazing such as Pyrodur, Pyrostop or Pyrobel systems is used depending on specification. Under fire conditions, intumescent seals around glass panels expand to restrict fire spread and limit smoke transfer. 

This makes glass fire doors suitable for corridors, stair cores and communal spaces where visibility and natural light are important design considerations. 

Intumescent seals, smoke seals and fire performance

Intumescent strips are a core safety feature in FD30 internal fire doors. When exposed to high temperatures, they expand to seal gaps around the door leaf and frame. This slows fire spread and helps maintain compartmentation. 

Smoke seals work alongside intumescent systems to reduce smoke leakage before and during fire development. Together, these components form part of passive fire protection systems that operate without mechanical activation. 

These safety features are critical in maintaining escape conditions and protecting occupants during evacuation. 

Design integration and internal applications

Crittall fire rated internal doors are designed to align with wider internal steel door systems. This allows consistent detailing across standard doors, flush fire doors and glazed screens within the same project. 

In refurbishment schemes, steel fire doors are often specified where existing openings require upgraded fire protection without compromising architectural intent. 

Internal French doors and larger glazed configurations can also be specified where tested systems allow, supporting open-plan layouts while maintaining compartmentation. 

Fire safety strategy and specification control

Fire rated internal doors form part of a wider fire safety strategy. This includes compartmentation design, escape route planning and structural fire protection. 

Specifiers must ensure that an FD30 rating aligns with fire strategy drawings and risk assessments. Early coordination reduces the risk of specification changes during construction and helps maintain compliance with building regulations. 

For property owners and developers, correct specification provides long term assurance that safety standards are being met and maintained. 

And finally…

FD30 fire rated internal doors are engineered systems designed to perform under controlled fire conditions as part of a wider safety framework. 

Within steel systems, Crittall fire rated doors provide tested performance, glazed fire resistance and compliance with UK fire safety regulations when specified and installed correctly. For architects, contractors and developers, the focus remains on complete assemblies, verified certification scope and correct installation to ensure fire safety requirements are met in practice. 

• For more information about Crittall’s fire rated doors, contact us here.