Fire Ratings for Flat Roof Systems: BROOF(t4) and Reaction to Fire Explained
BROOF(t4) is the highest classification for external fire performance of a roof under I.S. EN 13501-5, awarded after testing to CEN/TS 1187 Test 4, the method used in Ireland and the UK. It certifies that a complete build-up resisted penetration for 60 minutes under burning brands, wind and radiant heat. It is not a product property. It attaches to the specific assembly that was tested, so changing the membrane, the insulation, or its thickness can invalidate the classification.
BROOF(t4) is a rating for the complete roof build-up. Reaction-to-fire classifications such as A2-s1,d0 or B-s1,d0 apply to individual products. One cannot be used as evidence for the other.
Last technically reviewed: July 2026. Standards and guidance reviewed: I.S. EN 13501-1, I.S. EN 13501-5:2016, CEN/TS 1187:2012 and TGD Part B 2024. Project-specific fire engineering advice may still be required.
That distinction is where most specifications come unstuck. A schedule naming a BROOF(t4) membrane over an unspecified deck and an unrelated board has evidenced nothing, because the classification never belonged to the membrane. Below is what it certifies, how the test runs, what Irish guidance asks for, and what a defensible paper trail looks like.
What BROOF(t4) Actually Means
Break the designation into its parts:
B is the class achieved, the highest available under this test
ROOF signals the classification applies to roofs and roof coverings
(t4) identifies which of four test methods was used
The classification standard is I.S. EN 13501-5:2016. The testing standard is CEN/TS 1187:2012, which contains four methods. Both are listed among the referenced standards in TGD Part B 2024, Appendix E.
A BROOF(t1) or BROOF(t2) classification from a European manufacturer is not the same evidence, and buyers get caught by this regularly. Confirm which method applies to your project at TGD B clause 4.5.3, Classification of Performance.
Method | Exposure conditions | Principal national use |
t1 | Burning brands | Germany, Belgium, Netherlands |
t2 | Burning brands and wind | Nordic countries |
t3 | Burning brands, wind, supplementary radiant heat | France |
t4 | Two-stage: burning brands, then brands with wind and radiant heat | Ireland and the UK |
Two Different Fire Classifications Apply To Every Flat Roof
Question | BROOF(t4) | Reaction to fire |
What does it assess? | External fire performance of the complete roof | Contribution of an individual product to fire |
Governing standard | I.S. EN 13501-5 | I.S. EN 13501-1 |
Test basis | CEN/TS 1187 Test 4 | Product-specific Euroclass testing |
Applies to | Complete tested assembly | Individual material or product |
Typical designation | BROOF(t4) | A1, A2-s1,d0, B-s1,d0 |
Can one replace the other? | No | No |
An A2 insulation board does not give you BROOF(t4). A BROOF(t4) system does not tell you what class its components hold. Both belong in the specification, evidenced separately.
Inside The T4 Test, And What The Classes Mean
Test 4 is the most demanding of the four. A full build-up is assembled, including the deck, insulation, membrane, and surface finish, and then mounted at the pitch that represents the intended application.
The Preliminary Test
One specimen establishes burning behaviour after ignition. After withdrawal of the test flame, the specimen must burn for less than five minutes and flame spread must stay under 0.38m across the burning area for a B classification.
The Penetration Test
Further specimens face the combined attack: burning brands, forced airflow simulating wind, and radiant heat from a gas-fired panel. At least one specimen must include the joint details from each layer, which matters because joints are where real assemblies fail.
The Classes
Class | Performance under Test 4 |
BROOF(t4) | No penetration of the system within 60 minutes |
CROOF(t4) | No penetration within 30 minutes |
DROOF(t4) | Penetration occurs within 30 minutes |
EROOF(t4) | Lower performance still demonstrated |
FROOF(t4) | No performance determined |
Lower classes attract restrictions on proximity to a boundary. On a constrained urban site, that usually means the design changes rather than the distance.
What The Classification Covers, And What It Does Not
The classification belongs to the tested assembly, deck through to finished surface. It is not a property a membrane carries into any build-up it lands in.
Changes that can invalidate a classification report:
Substituting the waterproofing for an equivalent from another manufacturer
Changing insulation type, even at the same thickness
Increasing or reducing insulation depth
Altering the deck material or profile
Adding, removing or changing the cover board
Changing the surface finish, ballast or growing medium depth
Manufacturer requirement. Some systems hold extended application, or EXAP, reports permitting defined variation across a family of build-ups without retesting. Ask whether the report covering your build-up is a direct classification or an EXAP, and confirm your arrangement falls inside its declared scope.
What the classification does not tell you:
How components behave once fire is inside the building
Whether the deck satisfies structural fire requirements under B3
Whether penetrations and upstands are detailed correctly
Anything about smoke production or flaming droplets
What Irish Guidance Actually Requires
Irish regulatory guidance. Requirement B4 states that external walls and roof shall be designed and constructed so that they afford adequate resistance to the spread of fire over the face of the building, and to and from neighbouring buildings. Guidance is set out in TGD Part B 2024, Volume 1 for buildings other than dwelling houses, and Volume 2 for dwelling houses.
Check the transitional date. TGD B 2024 applies to works commencing on or after 1 May 2025, and the 2006 document ceased to have effect from that date, subject to defined transitional cases. The specifications written against the older document need to be rechecked.
Where to look inside Volume 1:
Section 4.5, Roof Coverings, covering classification of performance and separation distances
Table 22, Limitations on Roof Coverings, the operative table
Clause 4.5.7, Solar Panels on Roofs
Table 35, Appendix A5, giving notional designations for older national classifications
Table 13, reaction-to-fire classifications
One trap worth knowing: a part of a roof pitched at 70° or more to the horizontal may be treated as an external wall, which moves it out of the roof coverings provisions entirely and into the external wall requirements. Mansards are the usual place this bites.
A warning that matters more than anything else here: do not lift figures from UK Approved Document B and apply them to an Irish project. The regimes share the European classification system but set their provisions independently. The UK overwhelmingly writes content on this subject. Read TGD B, or ask a fire engineer.
Reaction To Fire And The Euroclass System
I.S. EN 13501-1 classifies individual products according to their contribution to fire growth.
Reading A Euroclass
Main class: A1, A2, B, C, D, E or F, running from no contribution to no performance determined
Smoke sub-class: s1, s2 or s3, with s1 the most limited smoke production
Droplet sub-class: d0, d1 or d2, with d0 meaning no flaming droplets or particles
TGD B defines A1 products as not contributing to fire growth at any stage, including the fully developed fire, and A2 products as not significantly contributing to fire load and fire growth under fully developed conditions. So B-s1,d0 describes limited contribution, very limited smoke and no flaming droplets. The document also uses A2-s3,d2 as the threshold in its definition of a fire break.
Where It Matters On A Roof
Stone wool sits at the top of the scale, which is why it recurs where fire performance drives selection. ROCKWOOL HARDROCK Multi-Fix dual density boards are described on their product page as presenting no smoke hazard and not contributing to fire growth at any stage, with LPCB approval to LPS 1181 Part 1 EXT-A. On façades, Rockwool Rainscreen Duo Slab plays the same role behind cladding. Request the declaration of performance and the certification record rather than relying on a statement in a brochure.
Green Roofs, Solar And Other Attachments
A green build-up complicates testing, since the methods were not written for saturated growing media. Guidance provides a route around it: a growing medium with a settled depth of at least 80mm and organic content not exceeding 50% by volume is treated as achieving the classification without further testing, provided the deck satisfies its own requirements.
Two cautions apply:
The 80mm is a minimum settled depth, so a roll-out system laid thin fails the assumption
Modular tray systems with plastic side walls cannot use this route and need testing or assessment
That guidance originates in UK documents, so confirm its standing with your Irish assessor. For rooftop generation, integrated systems such as BIPVco integrated solar are included in the classification, and TGD B addresses solar panels on roofs separately in clause 4.5.7.
What Evidence Should A Flat Roof Specification Include?
Assemble this before the fire safety certificate application, not after:
Classification report naming the complete tested build-up
EXAP report where variations are being relied upon
Declaration of performance for each relevant component
Confirmation of deck type and profile
Insulation product and thickness
Cover board specification
Waterproofing membrane and attachment method
Surface finish, ballast or growing medium depth
Tested pitch, and confirmation it covers the design pitch
Details of joints, penetrations, upstands and outlets
Confirmation that solar, plant or green components fall within scope
Project-specific confirmation against TGD Part B, Table 22
Frequently Asked Questions
What is a BROOF(t4) rating?
The highest external fire classification for a roof under I.S. EN 13501-5, achieved by testing the complete build-up to CEN/TS 1187 Test 4. It means the assembly resisted penetration for 60 minutes under burning brands, wind and radiant heat, with limited burning after the test flame was withdrawn. It applies to the tested assembly rather than any single product, so the classification report must cover your actual specification.
What is the meaning of a B-s1,d0 fire rating?
A reaction to fire classification under I.S. EN 13501-1 describing an individual product rather than a roof. B indicates limited contribution to fire growth, s1 very limited smoke production, and d0 no flaming droplets or particles. It is a different measure from BROOF(t4) and cannot substitute for it. Both may appear in a specification, evidenced by separate documents.
What does BROOF mean?
BROOF combines the class letter with the application. B is the class achieved, and ROOF indicates that it comes from external fire exposure testing of roofs rather than reaction-to-fire testing of materials. The bracketed suffix identifies which test method produced it. Classes descend through CROOF, DROOF, EROOF, and FROOF, with lower classes subject to restrictions on proximity to a boundary.
Can green roofs achieve BROOF(t4)?
Yes, by two routes. A complete build-up can be tested and classified conventionally, or, if guidance allows, a growing medium with a settled depth of at least 80mm and organic content below 50% by volume can be treated as compliant without further testing.
Modular tray systems with plastic side walls are excluded from the second route. Because that guidance is UK in origin, confirm its acceptance with your Irish assessor.
Talk To QBM Before The System Is Specified
QBM supplies BROOF(t4-) rated systems, non-combustible insulation, and passive fire protection products, and can provide the classification and performance documents for them. Because insulation, cover board, membrane and outlets come from one source, the assembly you specify is the assembly the paperwork covers.
Send through building type, deck type, proposed build-up, distance to the relevant boundary, and any solar, plant or green finish planned.
Email info@qbm.ie, call +353 1 839 1170, or use the enquiry form. Architects can request the RIAI-approved CPD session covering deck options, insulation and waterproofing.
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