Fire-Rated Windows Explained

What Is a Fire-Rated Window?

A fire-rated window is a window assembly designed and evidenced to provide a specified level of fire resistance.

The most important thing for builders to understand is:

A piece of fire-resistant glass fitted into a normal window frame does not automatically create a fire-rated window.

Fire performance relates to the complete system.

That can include:

• Frame profiles
• Glass
• Beads
• Gaskets
• Setting blocks
• Intumescent materials
• Fixings
• Anchors
• Perimeter fire stopping
• Supporting wall construction
• Maximum dimensions
• Installation method

The Quick Answer

If a drawing says:

EI30 WINDOW

do not simply ask your supplier for:

“30-minute fire glass.”

Instead ask:

“Can you supply a complete window system classified for EI30 in this size, configuration and supporting construction?”

That wording can prevent an expensive specification error.

What Does EI30 Mean?

Under the European fire-resistance classification system:

E = Integrity

I = Insulation

30 = 30 minutes

So an EI30 element is classified for 30 minutes in terms of both integrity and insulation, subject to the scope of its test/classification evidence.

Approved Document B expressly identifies E as integrity and I as insulation.

What Is Integrity?

Integrity relates to the element’s ability to resist the passage of fire/flames and hot gases through it for the stated period.

A pane remaining physically in position isn’t by itself enough to prove the complete window has the required classification.

The assembly is what matters.

What Is Insulation?

Insulation relates to limiting temperature rise on the non-fire side.

This is a major distinction between different fire-resistant glazing classifications.

Some systems may provide integrity without the same level of insulation.

That is why you cannot substitute:

E30

for

EI30

just because both say “30 minutes.”

EI30 vs EI60

Broadly:

EI30 = 30 minutes’ integrity and insulation.

EI60 = 60 minutes’ integrity and insulation.

The longer classification normally requires a system specifically tested/classified for that performance.

Do not assume an EI30 system can simply be upgraded to EI60 by fitting thicker glass.

Fire Glass Is Only One Component

The glass is critical, but so are:

• Frame
• Glazing method
• Beads
• Seals
• Blocks
• Fixings
• Intumescent components

Changing one element may take the construction outside its classification scope.

Aluminium Fire-Rated Windows

Specialist aluminium fire-resistant systems are available.

These often use:

• Dedicated thermally/fire-engineered profiles
• Specialist inserts
• Fire-resistant glazing
• Particular gasket/bead systems
• Specified fixing arrangements

A normal thermally broken commercial aluminium window should not be assumed to become fire resistant merely by changing the sealed unit.

Fixed vs Opening Fire Windows

Many fire-resistant glazed windows are fixed.

Opening fire-resistant windows are more complex because hinges, locking and sash movement introduce additional components.

If the architect requires an opening fire-rated window, establish very early whether a tested/classified configuration exists.

Do not price a conventional opening sash and plan to solve the fire rating later.

Maximum Sizes Matter

Fire-test/classification evidence has dimensional limits.

A supplier may have evidence for:

1000 × 1500mm

but that does not mean:

1800 × 2400mm

is automatically acceptable.

Check:

• Maximum width
• Maximum height
• Maximum area
• Glass orientation
• Mullions/transoms
• Frame configuration

before manufacture.

Supporting Construction Matters

A fire-rated window is installed into something.

That may be:

• Masonry
• Concrete
• Timber stud
• Metal stud
• Another fire-resisting wall system

The supporting construction may form part of the classification or installation requirements.

Don’t assume a window tested in masonry can automatically be fitted into any lightweight partition without assessment.

Perimeter Fire Stopping

Ordinary silicone around a fire-rated window is not automatically sufficient.

The perimeter detail may require specific:

• Mineral wool
• Fire-resistant sealant
• Intumescent material
• Backing materials
• Gap dimensions

Follow the system’s installation instructions and evidence.

Expanding Foam

This is another common site trap.

A generic can of expanding foam labelled:

“Fire rated”

does not automatically make it suitable for every fire-rated window installation.

The complete junction needs to match the approved/tested/assessed solution.

Fixings

Fixing type, spacing and edge distance can matter.

The installer should know:

• Required fixing material
• Diameter
• Spacing
• Position
• Minimum embedment

Do not install fire-resistant products using ordinary window-fixing habits unless they match the required detail.

Glass Orientation

Some specialist fire-resistant glazing products have orientation requirements.

Where relevant, ensure the glass is installed in accordance with the manufacturer’s instructions.

Don’t reverse panes or sealed-unit build-ups casually.

Fire-Rated Sealed Units

A fire-resistant window may incorporate an insulated glass unit where the tested/classified system permits it.

The complete build-up may combine:

• Fire-resistant pane
• Spacer
• Cavity
• Thermal/solar glass

Never change the external pane, spacer or cavity merely because the U-value or appearance needs improving without checking the system evidence.

Fire Rating and U-Values

A project may require both:

• Fire resistance
• Thermal performance

The window therefore needs to satisfy both.

Don’t solve Part B and accidentally fail Part L.

Similarly, glass changes made to improve thermal performance must remain within the fire-system evidence.

Fire Rating and Safety Glazing

The window may also be in a critical impact location.

Fire performance does not automatically demonstrate impact safety.

The specified glass/system needs to address all relevant requirements.

Fire Rating and Acoustics

Commercial projects may specify:

• EI30
• Acoustic Rw
• U-value

at the same time.

This is where generic window suppliers can struggle.

Always send the complete performance specification.

Documentation to Obtain

For fire-rated windows, retain suitable evidence including, where applicable:

• Classification report
• Product/system documentation
• Installation instructions
• Glass identification
• Hardware specification
• Permitted dimensions
• Supporting construction requirements

Keep this information with the project records.

Approved Document B states that European fire-resistance classifications should be supported by appropriate testing/classification, rather than simply assumed.

Installation Photographs

For commercial projects, create a proper installation evidence pack.

Photograph:

• Opening before installation
• Supporting wall
• Product labels
• Glass markings
• Fixing positions
• Frame perimeter
• Fire stopping before covering
• Finished seals
• Completed window

This can be invaluable when the main contractor, architect or Building Control later asks how the element was installed.

Site Alterations

Do not casually:

• Drill additional holes
• Change beads
• Replace glass
• Change seals
• Alter frame profiles
• Increase openings
• Change fixings

without establishing that the change remains supported.

Common Fire-Window Mistakes

Mistake 1 – “It’s fire glass, so it’s a fire window.”

Wrong.

Mistake 2 – Putting fire glass into a standard frame

That does not automatically provide a classified assembly.

Mistake 3 – Increasing the size

Fire evidence has scope limitations.

Mistake 4 – Changing the sealant

Perimeter materials can be critical.

Mistake 5 – Ignoring the supporting wall

The substrate matters.

Mistake 6 – Treating E30 as EI30

They’re different classifications.

Mistake 7 – No installation photographs

This makes later verification much harder.

Real-World Example

An architect specifies:

EI30 fixed aluminium window – 1200 × 1800mm

The contractor obtains a quote for specialist EI30 glass and proposes fitting it into a standard aluminium commercial window.

That approach is fundamentally flawed.

The contractor needs a complete fire-resistant window system with evidence covering:

• EI30 performance
• Proposed dimensions
• Glass
• Frame
• Supporting construction
• Installation method

The glass certificate alone is not enough.

Builder’s Fire-Window Checklist

Before ordering, confirm:

• Required classification: E, EI, EW, REI etc.
• Required duration: 30, 60, 90 minutes etc.
• Fixed or opening
• Width and height
• Supporting wall construction
• Internal/external exposure requirement
• U-value
• Safety glazing
• Acoustic requirement
• Frame material
• Finish
• Installation detail
• Evidence required by contractor/Building Control

Frequently Asked Questions

What is an EI30 window?

A window assembly classified for 30 minutes’ integrity and insulation within the scope of its evidence.

Is EI30 the same as 30-minute fire glass?

No. The complete window assembly matters.

Can I put EI30 glass in a normal aluminium frame?

That does not automatically create an EI30 window.

Can aluminium windows be fire rated?

Yes, specialist tested/classified aluminium systems are available.

Can a fire-rated window open?

Some specialist systems may allow opening configurations, but these need appropriate evidence.

Does fire-rated expanding foam make the installation compliant?

Not by itself.

Can I change the glass specification?

Only if the revised construction remains supported by appropriate evidence.

Is E30 the same as EI30?

No.

Does fire-rated glass also count as safety glass?

Not automatically. Check the relevant impact classification.

Related Guides

• Part B Explained
• REI30 vs EI30
• Toughened Glass Regulations
• Laminated Glass Guide
• Fire-Rated Doors
• Building Control Checklist

Trade Tech Technical Support

For fire-rated window enquiries, send the full specification before requesting a price.

At minimum provide:

• Required fire classification
• Duration
• Sizes
• Window configuration
• Supporting wall type
• U-value
• Acoustic requirement
• Safety-glazing requirement

Important: Fire-rated glazing is a system-performance issue. Never substitute glass, frame components, fixings or installation materials without checking the applicable classification/test/assessment evidence.