Why is flat roof fire rating important?

Converting roof spaces into accessible areas means that the materials used for these conversions need to meet fire safety standards.

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The Grenfell Tower fire of 2017 highlighted major shortcomings in the fire resistance of construction materials used on the outside of high-rise buildings in the UK. In 2019 the UK national classification system for fire rating of roof materials (BS 476-3:2004) was replaced by European Classification System BS EN 13501-5.

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Under the new system, roof materials are classified under one of five ratings:

• BRoof(t4)
• CRoof(t4)
• DRoof(t4)
• ERoof(t4)
• FRoof(t4)

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But what do these mean?

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What is t4?

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To comply with BS EN 13501-5 classification, materials must undergo four tests:

• With Test 1 the material is exposed to a burning brand
• With Test 2 the material is exposed to a burning brand and wind
• With Test 3 the material is exposed to a burning brand, wind and an additional source of radiant heat
• Test 4 is similar to Test 3 but includes testing for external fire spread and penetration by fire.
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All tests involve a preliminary test being applied to one specimen of the material, followed by a subsequent test being applied to a further three specimens.

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B–F: What are the differences?

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Materials with a B rating score the highest in terms of resistance, while those with an F score lowest.

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FRoof(t4)

• Specimens will have undergone Test 4 but no fire performance will have been determined.

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ERoof(t4)

• Preliminary testing
• no penetration
• Subsequent testing
• penetration within 30 minutes
• spread of flame not controlled

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DRoof(t4)

• Preliminary testing
• no penetration
• flame spread less than 0.38 metres
• Subsequent testing
• penetration within 30 minutes
• burn for less than 5 minutes after flame withdrawn

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CRoof(t4)

• Preliminary testing
• no penetration
• flame spread less than 0.38 metres
• Subsequent testing
• no penetration within 30 minutes
• burn for less than 5 minutes after flame withdrawn

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BRoof(t4)

• Preliminary testing
• burn for less than 5 minutes after flame withdrawn
• flame spread less than 0.38 metres
• Subsequent testing
• no penetration within 60 minutes

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A BRoof(t4) classification is referred to as ‘unrestricted’ in England and ‘low vulnerability’ in Scotland, which means it can be used anywhere on the roof.

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CRoof(t4) requires a minimum gap of 6 metres between the boundary of the roof and surrounding buildings.

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DRoof(t4) and ERoof(t4) require a gap of 6, 12 or 20 metres, depending on the type of adjacent building and its use, while FRoof(t4) requires a minimum gap of 20 metres.

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Our system going through the BRoof(t4) testing process

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BRoof(t4) achieved!

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What roof terrace materials comply with BRoof(t4)?

A roof terrace system is comprised of several components – pedestals, joists, decking – which all need to comply.

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The Raaft terrace system has been designed to fully comply with BRoof(t4).

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• All joists are made out of extruded aluminium, which is a BRoof(t4) compliant material. While they feature a rubber strip, this doesn’t contribute to the spread of fire, so is allowed under BRoof(t4).
• The steel used to make metal adjustable pedestals is also BRoof(t4) compliant. Some use plastic tile spacers, but these are allowed under the classification.
• Porcelain – used for stone-effect tiles and woodgrain-effect planks – is another naturally BRoof(t4) compliant material.
• The steel and surface coatings used to make planter systems are also BRoof(t4) compliant.

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BS EN 13501-5 compliance isn’t a factor you can afford to take chances with when converting a flat roof. For impartial, professional advice on how to ensure your project meets all the regulations, contact Raaft on +44 (0)20 3146 7879 or at enquiries@raaft.co. Alternatively, send us a message via the website enquiry form and one of the technical support team will respond promptly.

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