Fire Window Product Comparison: E30 vs E60 vs EI60

The Fire Window Codes That Could Save—or Doom—Your Build

The design was immaculate. Planning consent secured, the contractor mobilised, and windows already in fabrication. Then came the halt: a single notation in the schedule—“E60.” It should have read “EI60.” That one missing letter triggered a six-week delay, forced re-specification, and placed the entire fire strategy under review.

This is no anomaly. Across the UK, developers, architects, and specifiers are encountering similar setbacks, not due to poor workmanship or flawed design, but because of a critical misunderstanding in fire compliance terminology. E30. E60. EI60. To the unfamiliar, they appear interchangeable. In reality, they represent fundamentally distinct levels of protection with profound implications for safety, compliance, and project delivery.

The distinction is not merely academic. Misapplying a fire rating can mean the difference between a signed-off inspection and a forced redesign, between a compliant escape route or a corridor rendered hazardous under radiant heat. These codes carry regulatory weight and operational risk. And in a regulatory environment that demands both precision and foresight, misunderstanding them is a costly misstep.

This article sets out to clarify those distinctions and arm specifiers with the insight needed to avoid disruption. Because in today’s compliance climate, the ability to interpret a fire rating correctly isn’t just best practice—it’s a professional imperative.

What Do These Fire Ratings Really Mean?

Fire ratings are not just regulatory codes—they are performance thresholds that determine how long a window will resist fire, and in what way. The “E” in E30 or E60 denotes integrity: the ability of the window to remain structurally stable under fire exposure for 30 or 60 minutes, without allowing flames or hot gases to penetrate. It means the unit won’t break apart, but it says nothing about how much heat passes through.

And that’s the critical oversight.

Windows rated for integrity alone can still allow radiant heat to pass at lethal levels. In protected corridors or escape routes, this creates a hidden hazard: a zone that appears safe but quickly becomes impassable due to unbearable temperatures. The structure may hold, but the space beyond it becomes compromised.

That’s where the “I” matters. EI60 windows are tested and certified for both integrity and insulation. For a full 60 minutes, they block not only flames but also the transmission of heat. This distinction is what ensures escape routes remain usable, firefighters can safely engage from protected areas, and insurers recognise reduced risk. It also significantly reduces the likelihood of Building Control rejections.

EI60 units carry a premium, typically due to the specialist glazing compositions, framing systems, and full-system testing they require. But in high-risk zones, the cost of not specifying them is often far greater. Delays. Redesigns. Failed inspections. And, in the worst cases, liability in the event of a fire.

Understanding the nuance behind these ratings is no longer optional. For specifiers working in multi-unit housing, heritage conversions, or commercial developments with compartmentation, it is a fundamental aspect of compliance leadership.

Which Rating Do You Really Need?

Here’s the truth: most buildings need EI60 fire-rated glazing—but only realise it too late. Here’s why:

• If your window borders a protected escape route, EI60 isn’t a luxury. It’s required.
• If it separates a habitable room from a circulation space, the heat transfer risk demands EI60.
• If you’re in a conservation area, EI60 units designed for heritage joinery are available, and pre-approved packs reduce planning delays.

The critical point isn’t whether the glass is labelled fire-rated. It’s whether it’s certified under EN 1634-1 and classified under EN 13501-2 with both E and I ratings. It must have documented, test-backed performance that Building Control trusts—and planners accept.

If you’re still using E30 or E60 without insulation, and assuming it’s “close enough,” you’re gambling with every schedule line, invoice, and inspection you’ve worked for.

Why Do Projects Fail This Spec?

Failure happens in silence. A joiner selects an E60 unit. It looks robust. It matches the dimensions. It’s even labelled “fire-rated.” But no one checks the insulation rating. There’s no cert for radiant heat resistance. The Building Control officer sees the spec, sees the corridor position, and blocks it. Because to them, E60 without insulation is a non-starter.

You lose six weeks. Pay to replace. Possibly resubmit for planning if the new unit alters sightlines. All because one letter was missing.

This is not rare. It’s systemic.

EI60: Your Strategic Spec Advantage

Those who specify EI60 from the start aren’t just “playing it safe.” They’re:

• Preempting Building Control objections
• Aligning with Part B of the UK Building Regulations
• Accelerating sign-off in sensitive or single-stair schemes
• Protecting life—and reputation—with heat-blocking performance
• Increasing the resale and insurance confidence of the building

With pre-tested, conservation-approved EI60 sash windows now available, the old arguments of “but the heritage officer won’t approve it” or “we can’t source it in time” no longer hold. You can get EI60 that looks heritage, acts modern, and arrives with a full approval pack—CAD, certs, thermal declarations, and more.

Get Ahead: Tools That Eliminate Spec Guesswork

If you’re unsure what your floor plan needs, don’t guess.

• Upload your layout to our compliance team and receive a spec-by-zone map in 48 hours.
• Or download the EI60 Officer-Approved Spec Pack—containing tested products with install guides and certification.
• Book a Fire Spec Consultation to review your requirements before buying.

What is the difference between E60 and EI60? It’s the space between passing and failing. Between protecting lives and exposing risk. Between the project you planned and the one you’ll be explaining to insurers.

Don’t let a missing “I” cost you everything.

The Test That Separates Fact from Fiction: EN 1634-1 in Detail

At the heart of fire-rated window compliance is a test so critical, its absence can nullify a whole schedule: EN 1634-1. This is not a label. It is not a verbal assurance from a supplier. It is a legally recognised, destructive fire test that simulates how a glazed unit performs under full flame exposure in a controlled lab environment.

During this test, the window is subjected to temperatures exceeding 800°C within the first 10 minutes, rising beyond 1000°C by the half-hour mark. To pass the E rating, the unit must maintain integrity: no flaming, no openings, no glass blowout that would allow fire to spread. But to achieve EI, the bar is raised. The window must also resist the transfer of heat through the frame and glass. Surface temperature must not rise above 140°C on the protected side for 60 full minutes. That’s the real test—and few products pass it.

The outcome is binary in the eyes of Building Control: either your product has an EN 1634-1 certificate issued by a recognised lab, or it doesn’t. There is no grey area. And without that certificate, your fire window, regardless of the manufacturer’s claims, won’t be accepted on high-risk projects. Not for flats. Not for escape corridors. Not for conversions or mixed-use refurbishments in conservation areas.

So why do developers still fail this step? Because too many window providers treat “fire-rated” as a marketing term, not a certified outcome. Because specifiers still assume “glass is glass” if the frame looks right. Because no one wants to ask the awkward question: “Can I see your EN 1634-1 cert, and is it valid for this configuration?”

Frames That Fail Before Glass Does

One of the great paradoxes in fire window design is that many products that pass the integrity or insulation test in isolation don’t perform once built into a real window. Why? Because the frame is the first thing to go.

Wood swells. Steel deforms. Aluminium softens and warps. Even when the glass is rated for 60 minutes, the frame surrounding it must also survive without distorting, cracking, or transferring heat. And that’s where the danger lies.

For example, an EI60 glass unit installed in a timber sash window might seem compliant. But if the timber lacks the proper intumescent seals, subframe breaks, and test-backed joinery detail, it won’t pass the test. It becomes a façade—an illusion of safety.

The solution? EI60 windows must be designed and tested as a unit: glass + frame + ironmongery + fixings. The test applies to the complete assembly, not just one component. That’s why sourcing EI60 glazing independently from your joiner is risky. It’s also why we always advise using system-tested, fully certified EI60 windows provided with an Approval Pack—CAD, test cert, and full installation detail.

This isn’t optional. It’s a survival strategy for both your building and your compliance schedule.

Planning Officers vs Building Control: The Hidden Tug of War

Specifying fire-rated windows isn’t just about certification. It’s about navigating two very different worlds: planning approval and fire safety compliance. And they often conflict.

Planning officers want heritage aesthetics. Slim sightlines. Traditional mouldings. Timber grains that look hand-finished, even on a third-floor elevation. Meanwhile, Building Control cares about what happens after a fire starts: whether the sash locks shut under pressure, whether radiant heat scorches a stairwell, whether a child has a survivable corridor to run through.

This conflict leaves developers and architects stranded between departments that don’t speak the same language. Your planning drawings are approved with a beautiful slimline E-rated window, then rejected weeks later by Building Control because the product lacks insulation performance.

This is where strategic specification matters. Today, there are EI60 sash windows designed for conservation zones. They look like traditional joinery. They use laminated hardwood or hybrid composite timber, intumescent liners, and heritage-approved sightlines. And most importantly, they’re tested and certified.

By presenting pre-approved heritage EI60 window packs with your planning submission, you bridge the divide. Planning officers see aesthetic compliance. Building Control sees safety. Your project flows forward, not into resubmission limbo.

And that difference? It’s worth months in saved time and thousands in preserved margin.

Cost Analysis: The Price of Protection

For developers and architects navigating tight margins, few things induce more hesitation than the price tag of fire-rated windows, especially EI60 units. The jump from E30 to EI60 can feel steep. A window priced at £450 for a 30-minute integrity can soar past £1,100 when insulation and full-system certification are factored in. It’s tempting to cut corners or gamble on lower-rated units. But the hard truth is this: when fire compliance is treated as a cost rather than a risk mitigation tool, the real price often shows up months later—buried in delay penalties, re-specification fees, and emergency redesigns.

Let’s make it tangible. A five-flat development in a London conversion might call for seven sash windows bordering escape routes. Using uncertified or mismatched E60 windows could save £4,000 up front. But if Building Control flags them at final inspection—triggering a re-spec and reinstallation—the developer not only eats the cost of replacement (now rushed at a premium), but also delays practical completion. That means more interest in bridging loans, postponed sales or lettings, contractor holding costs, and reputational fallout.

It gets worse if planning re-approval is required. A replacement EI60 unit with slightly wider frames or altered glass-to-timber ratio might no longer match the original elevation drawings. This isn’t a hypothetical—it’s an expensive domino chain that’s become increasingly common post-Grenfell, as fire regulations face tighter enforcement and zero-tolerance interpretations by local authorities.

What You’re Really Paying For

When you choose EI60 from the outset, the added cost isn’t just for materials. It’s for certainty. You’re paying for:

• Pre-tested system integrity: Full units tested to EN 1634-1, not just components
• Building Control acceptance: Faster approvals and reduced inspection disputes
• Fire escape assurance: Thermal insulation that gives residents survivable routes
• Planning continuity: Heritage-compatible frames that avoid design alterations
• Litigation protection: Product documentation that stands up in court, if needed

Developers working in complex schemes—like single-staircase flats, HMO conversions, or listed building refurbishments—understand that the real cost of compliance isn’t the price of the window. It’s the cost of having chosen the wrong one.

And it’s not just the upfront cost. EI60 windows, when system-tested and supplied with full documentation, often qualify for reduced fire engineering scope. That means you may offset EI60 investment with savings elsewhere: thinner fire curtains, reduced reliance on mechanical extract systems, or simplified sprinkler placement. When analysed properly, EI60 can be a strategic cost reducer, not just a line-item add.

Value Preservation vs Cost Saving

Consider a second-tier development on the edge of a conservation zone. The team goes with E60 to match timber aesthetics but skips insulation. The project is near completion when the fire inspection fails the corridor rating. The new EI60 unit now requires 8–10 weeks for manufacture. Completion slips. Marketing timelines stall. Buyer confidence drops. The project is now worth £45,000 less than projected—not because the architecture failed, but because a single spec decision wasn’t future-proofed.

Contrast that with a developer who budgets EI60 from the start. Their project completes on time. Marketing materials cite fire-resilient features. Surveyors list the units with confidence. Lenders reduce contingency holdbacks. That £700 difference per unit buys more than 60 minutes of resistance—it buys brand equity, delivery predictability, and higher buyer trust.

EI60 isn’t just a performance spec. It’s a business asset.

Where to Use What: Spec by Location

It’s not the fire that gets you—it’s the smoke, the heat, and the paperwork.

Most window specification errors don’t happen because developers or architects choose the wrong product. They happen because the right product is placed in the wrong zone. And when fire strategy meets building layout, location dictates everything.

Let’s start with the basics. A fire-rated window isn’t a uniform requirement—it’s a context-specific solution. Whether you need E30, E60, or EI60 depends entirely on what the window overlooks, separates, or protects.

Corridor Facing? EI60 or Nothing

If a sash window opens onto an escape corridor, the stakes rise exponentially. This isn’t just a design detail—it’s a life safety zone. That corridor must remain passable for at least 30–60 minutes during a fire. An E60 unit might block flames, but radiant heat will still pour into the corridor, rendering it impassable within minutes. This is a direct breach of Approved Document B and typically results in Building Control rejection.

In this scenario, only EI60 units offer the insulation needed to keep escape routes viable.

Inter-room Windows: The Grey Zone

Now consider internal windows—like a glazed panel between a kitchen and a stairwell, or a sidelight facing an atrium. If the partition forms part of a compartment wall or fire separation zone, the integrity and insulation rules apply again. Yet many projects still install basic E-rated or non-rated glazing in these transitional zones.

The consequence? In a fire, the heat builds rapidly. Flames don’t need to cross the glass—the thermal radiation alone can ignite materials, collapse plaster, or incapacitate escapees. The solution? EI30 or EI60, depending on your layout and the fire engineer’s input.

External Elevation? Context is King

What about windows on external elevations? It depends on two things:

1. Proximity to boundary – If your window is within 1 metre of a neighbouring property, regulations may require it to be fire-rated to prevent lateral fire spread.
2. Position relative to escape routes – If the window borders a protected corridor or stairwell, and the elevation poses re-entry risk from flame ingress, you may still need EI-rated glazing.

Don’t assume “outside” means safe. The test isn’t “Will it burn?” It’s “Will it keep others from burning too?”

Floorplan Reading: A Fire Officer’s Mindset

To truly spec windows correctly, stop thinking like a designer and start thinking like the fire officer reviewing your layout.

Ask:

• Where will smoke accumulate?
• What zones must stay clear long enough for evacuation?
• Which windows act as passive fire barriers, not just views?

Mapping these relationships is not just smart—it’s strategic. It empowers you to assign EI60 where it’s vital, E60 where it’s sufficient, and non-rated units where permissible, all without second-guessing approval.

To streamline this, we offer:

• Free Floorplan Review: Upload your design, and we’ll return a zone-spec matrix within 48 hours.
• Fire Zone Spec Pack: A downloadable PDF with annotated diagrams and layout-specific recommendations.

Because clarity isn’t just compliance—it’s control.

Common Mistakes & Silent Failures

It’s not the roaring inferno that sabotages your build—it’s the quiet oversight, the missing cert, the unit that “looked compliant” but failed in silence. In the world of fire-rated windows, most failures happen long before a match is struck.

Builders, developers, and architects often assume that specifying “fire-rated” glass is enough. But the real-world system that gets inspected by Building Control, fire engineers, and insurance underwriters is more than just a label. It’s a web of performance data, installation accuracy, and material interactions. Get any part wrong, and the consequences cascade.

Let’s dissect the most common—and most costly—mistakes in fire window specification and installation.

Mistake 1: Assuming E60 Is ‘Close Enough’ to EI60

This is the most pervasive and dangerous misunderstanding. E60 protects against flames only, not the heat that can radiate through glass, ignite materials on the safe side, and compromise escape routes. Many specifiers order E60 units for protected corridors, thinking they’ve met the 60-minute threshold. They haven’t. And Building Control catches it fast.

EI60 isn’t just a higher number—it’s a fundamentally different class of protection. If insulation isn’t tested, it doesn’t exist. And if it doesn’t exist, your window is a liability.

Mistake 2: Relying on Component Certification, Not System Certification

Manufacturers may show you a certificate proving that their glass passed EN 1634-1. But was it tested with the exact frame, fixings, and sealants you’re using? If not, it means nothing. EN 1634-1 applies to the entire assembly, and any change—timber type, beading, locking system—can void the rating.

Silent failure occurs when:

• Joiners swap out components for “ease of install”
• Contractors source frames locally, assuming they match spec
• Test certs are filed without confirming the unit’s configuration

And when the inspector sees that discrepancy? Expect a fail.

Mistake 3: Misaligned Specs Between Planning and Building Control

One of the most frustrating causes of delay is the spec mismatch between what Planning signs off and what Building Control demands. Planning officers often approve windows for visual alignment—slim frames, heritage sightlines—without confirming fire rating viability. Then, during construction, the fire consultant insists on EI60 units with different dimensions or visible differences.

Suddenly, you’re caught between departments with opposing requirements. To resolve it, you need:

• Pre-approved EI60 windows with heritage visual profiles
• Documentation bundles showing both Part B and aesthetic compliance

Skipping this step isn’t saving time. It’s loading a delay into your schedule—one that detonates months later.

Mistake 4: No Installation Verification Protocol

Even a perfectly rated EI60 unit can fail on site if it’s installed incorrectly. That means:

• Screws in the wrong location
• Missing intumescent liners
• Over-trimmed sealants
• Gaps at the interface with the surrounding walls

Each of these errors, invisible to the untrained eye, can nullify the entire certification. It’s why we recommend:

• Supplying installer guides with each unit
• Requiring sign-off checklists for fire-rated glazing installation
• Using system-specific EI60 windows with manufacturer-trained install partners

If you’re not tracking the install, you’re not protecting the spec.

Planning, Approval, and Installation Risk

Fire compliance doesn’t live in a product brochure—it lives in the quiet, conflicting expectations of two separate authorities: Planning and Building Control. And if you haven’t already felt the tension between the two, consider yourself lucky. Because most developers working on heritage or mixed-use refurbishments hit a wall right here: the window looks perfect on paper, but fails in practice.

The problem is not malice. It’s misalignment.

Planning officers judge a window by its appearance. They assess elevation drawings, proportions, glazing lines, and historic continuity. Their approval is largely visual. Meanwhile, Building Control cares about performance—whether that beautiful sash will resist flame and heat for 60 minutes, or buckle under seven. This disconnect causes one of the most expensive and time-consuming types of project failure: post-approval window rejection.

The Paper Trail That Kills a Build

Here’s how the trap is set:

1. You submit planning drawings with slender-profile, non-insulated E-rated glazing to match conservation guidelines.
2. Planning approves the design. You order frames, set delivery schedules, and coordinate joinery.
3. During fire strategy review, Building Control sees the same window, now scheduled into an escape corridor, and rejects it due to missing insulation performance.
4. You scramble to find an EI60 alternative, but the thicker profiles no longer match the approved elevations.
5. You must reapply to planning. Everything halts.

The window was the same. But two departments viewed it through two different lenses.

This isn’t just frustrating—it’s financially ruinous. Every week of delay costs in holding costs, contractor extensions, and buyer confidence erosion. You don’t just lose time. You lose momentum.

How to Future-Proof Against Fire Spec Rejection

The solution is a dual-approval mindset. From the moment you specify a fire-rated window, you must assume both departments will scrutinise it, and that the product must satisfy both aesthetics and performance.

Here’s how to get ahead:

• Use EI60 units that are heritage-approved, with documented tests showing slim sightlines and full insulation performance.
• Include fire certs in your planning submission pack—even if not required, it signals diligence and prepares the pathway for Building Control.
• Source from manufacturers offering CAD files, Part B compliance data, and visual reference documents so both officers sign off faster.

Even better, work with suppliers offering pre-approved EI60 sash window packs. These bundles include:

• EN 1634-1 test certificates (system-specific)
• Conservation-compliant drawings
• U-value declarations
• Installation guidance
• Fixing and joint specifications
• Acoustic and thermal reports, when applicable

That’s not a product. That’s an insurance policy for your project timeline.

Installation Is the Final Gate

Even with perfect planning and product spec, your project can still fail if installation is overlooked. Fire-rated windows are not like standard joinery. A misplaced screw, an incorrect packer, or an absent intumescent seal can nullify the entire certification.

Best practice isn’t optional—it’s enforceable:

• Use trained, certified installers familiar with EI-rated systems
• Request post-install checklists with photographic evidence
• Conduct a fire-rated installation audit during snagging
• Keep documentation on file for post-completion and insurance

What matters to Building Control is what goes in, not what was ordered. A failed install looks the same as a failed spec. And in both cases, the result is the same: delay, cost, and risk escalation.

Which Spec Wins? The One That Survives the Fire—and the Committee

There’s a moment in every project where everything seems perfect. The joinery is millimetre-precise. The glazing reflects the afternoon light like a postcard. The planning officer nods approvingly. But then the Building Control officer arrives—measuring, checking, verifying. And within minutes, that perfection unravels.

Why?

Because the spec wasn’t built to survive scrutiny. It was built to survive the brief.

In 2025, with fire safety reforms reshaping the landscape post-Grenfell, the winning specification isn’t just the one that looks good or fits the budget. It’s the one that passes inspection, aligns with performance regulations, and outlasts the fire—on paper and in reality.

And that spec, increasingly, is EI60.

The New Standard of Leadership in Fire Window Spec

EI60 has emerged as more than just a rating. It’s a statement of foresight, responsibility, and control. Specifying EI60 doesn’t just signal technical compliance. It shows that you:

• Understand risk
• Anticipate regulatory scrutiny
• Prioritise occupant survival
• Protect project timelines from bureaucratic ambush
• Align aesthetic heritage with modern safety

When you choose EI60 from a system-tested, officer-approved supplier, you’re not just sourcing a product. You’re deploying a strategy.

It says to the conservation officer: “We respect the heritage.”
It says to Building Control: “We’ve already passed your test.”
It says to clients, surveyors, and insurers: “We planned for everything—including the worst.”

The Hidden ROI of Getting It Right the First Time

Across hundreds of builds, the financial model repeats:

• Upfront EI60 cost: +£400 per unit
• Avoided delays: -£12,000 average in holding & redesign costs
• Enhanced buyer confidence: +£25k–£50k in sales uplift across scheme
• Insurance premium reduction: 3%–5% per unit annually in some cases
• Developer stress, reputation, and legal exposure: immeasurable

Specifying EI60 isn’t just an investment in glass and timber—it’s a bet on your professional legacy. Because the project that is completed on time, on budget, and without post-inspection scrambling is the one that builds trust and repeat business.

And in a market where developers are increasingly held accountable for post-occupancy safety, that trust is a currency more valuable than margins.

Appendix: Fire Window Specification Quick Reference

For those needing a rapid comparison or specification guide, here’s a concise breakdown of the most relevant fire window classes discussed throughout this article, based on EN 13501-2 classifications and EN 1634-1 test performance.

Note: Always verify if the tested unit was assessed as a system (glass + frame + fixings) under EN 1634-1. Independent test data from a UKAS-accredited lab is mandatory for certification.

Frequently Asked Questions (FAQ)

Is E60 the same as EI60?

No. E60 windows provide 60 minutes of integrity only—they resist flame but not heat. EI60 windows resist both flames and radiant heat, keeping escape routes safe and preventing heat ignition beyond the barrier.

Can I install E60 in a protected corridor?

Usually not. Protected corridors require insulated units (EI30 or EI60) to prevent heat transfer. Installing E60 in these locations can lead to Building Control rejection.

Will EI60 windows be accepted in conservation areas?

Yes—if sourced correctly. EI60 units designed for heritage joinery are now available with pre-approval packs including elevation drawings, timber specs, and conservation-aligned profiles.

Is certification required for each component or the whole window?

Certification must be for the entire window system—glass, frame, seals, ironmongery—tested together under EN 1634-1. Partial certification is not valid for compliance.

What if the installer modifies the unit during fitting?

Any deviation—cutting seals, incorrect fixings, omitting intumescent layers—voids certification. Always use trained installers and maintain documented installation protocols.

Strategic Resource Deployment

To accelerate project approval and prevent fire-spec failure:

• Request our EI60 Heritage Window Spec Pack (includes CAD files, Part B compliance, thermal declarations)
• Submit your floor plan for a free Fire Strategy Audit – zone-by-zone guidance within 48 hours
• Book a Compliance Walkthrough with a senior fire consultant—align aesthetics, fire safety, and planning from day one