After the Grenfell disaster in 2017, new regulations around not only roof garden fire safety but all aspects of buildings, now ensure we are all as safe as we can possibly be were introduced. New ratings of fire protection are now in place, and these are achieved by rigorous testing procedures that determine the grade of roofing material and thereby whereabouts on the roof this can be placed.
The area of highest fire danger on a roof is directly over a wall or vertical structure as fire will naturally travel up a wall and by that, gain access into a roof or onto a roof garden. If the roof is easily penetrated by the fire and the fire spreads quickly, lives could easily be in danger. The regulatory authorities have tried to combat this with the new rating system to make sure that such a situation will hopefully never occur.
Roofing ratings for materials come in five European classes: Broof(t4), Croof(t4), Droof(t4), Eroof(t4) and Froof(t4).
Broof(t4) is a term relating to the highest fire resistance rating of combustible materials. An A-grade material does not combust, and these 5 other grades show varying degrees of resistance. The chart below shows how materials comply with the different grades and whereabouts on the roof so that they can be used. (Note t4 refers to the type of test used and is not a measure for resistance. Test 4 – A British two-stage method incorporating burning brands, wind and supplementary radiant heat).
|Classification for roofs/roof coverings exposed to external fire||Minimum distance from any point on relevant boundary (England)||Minimum distance from any point on relevant boundary (Scotland)|
|Broof (t4)||No penetration of roof system within 60 minutes In preliminary test, after withdrawal of the test flame, specimens burn for less than 5 minutes In preliminary test, flame spread less than 0.38m across region of burning||Unrestricted and can be used anywhere on the roof||Low Vulnerability (<6m)|
|Croof (t4)||No penetration of roof system within 30 minutes In preliminary test, after withdrawal of the test flame, specimens burn for less than 5 minutes In preliminary test, flame spread less than 0.38m across region of burning||At least 6m from the boundary||Medium Vulnerability (6-24m)|
|Droof (t4)||Roof system is penetrated within 30 minutes but is not penetrated in the preliminary test In preliminary test, after withdrawal of the test flame, specimens burn for less than 5 minutes In preliminary test, flame spread less than 0.38m across region of burning||At least 6,12 or 20m from the boundary depending on the building type and use||Medium Vulnerability (6-24m)|
|Eroof (t4)||Roof system is penetrated within 30 minutes but is not penetrated in the preliminary test Flame spread is not controlled||At least 6,12 or 20m from the boundary depending on the building type and use||High Vulnerability (>24m)|
|Froof (t4)||No performance determined||At least 20m from the boundary depending on the building type and use||High Vulnerability (>24m)|
Legally, the top of a wall that is connected or fixed to a roof or ceiling needs to be surrounded by 1500 mm of Broof(t4) grade materials in all horizontal directions. This is generally a concrete roofing platform that acts as a barrier, or similar tested material that has been approved by the necessary authorities. ‘Warm’ roofs must have a fireproof laminate on both sides of the insulation 1500 mm around a wall or support to ensure that it is compliant. Most architects, however, tend to cover all the insulation in fireproofing to exceed the expected standards.
Our planter edging is made from galvanised mild steel and as it is a non-combustible, durable, fire-resistant material, it is compliant with the Broof (t4) specifications. Although our products have not been tested as a planter, this is acceptable under B8; Appendix B of The Building Regulations Act 2010, which states ‘To reduce the testing burden on manufacturers, BS EN 13238 defines several standard substrates that produce test results representative of different end-use applications.’ Mild steel has been tested and it has been certified that it does not contribute to fire heat or spread the fire.
If planters are coated in a powder-coated finish, does this contribute to the fire? The short answer is no, and that the steel maintains its Broof (t4) compliance. Powder-coated finishes are baked onto the metal surface, and so, therefore, cannot be flammable as they would ignite in the kilns during manufacture. To ensure that they never ignite inside one of the curing ovens, the powder coating does not contain any volatile organic compounds (VOCs) which are responsible for the combustion of most materials. This intended lack of VOC’s means that all our planters are therefore Broof (t4) compliant.
Please see our Insight on https://logic-bespoke.com/is-timber-suitable-for-roof-terraces/ for information around seating and wooden furniture at roof level on roof garden spaces.
There are several steps that architects can take to help prevent roof garden fires. First, they can specify fire breaks which go down to the concrete or hardcore and prevent fire from spreading along pedestals etc. on the outside surface of the roof. The second step is to carefully consider the plant species that they specify. No plants on a roof terrace could contribute to a fire.
Legally, roof gardens should have fire breaks every 40m that are 500mm wide and 50mm deep. These can come in many forms such as paving slabs or a packed gravel break and are generally used to make paths etc. However, slabs and decking sitting on pedestals do not make the grade with all that extra plastic underneath. Our steel planters can help architects combat this by providing the necessary compliance without any alterations. The steel planter edge goes down below the surface of the paving to the packed non-combustible surface below. This creates an effective firebreak.
The fire break mustn’t be breached otherwise it will become completely ineffective. It may be necessary to mix our planters in with other forms of breaks in order to suit a particular job.
Plant choice is very important for every architect and is even more important at the roof level. Plants that contain high amounts of resins or oils should be avoided as they may contribute to a fire, as should plants that are apt to dry out at certain times of year such as grasses and mosses. Plants such as sedums with high water content should be given priority.
Adequate irrigation systems are also necessary so that they can be used to help prevent fire in an emergency.
Although there is a lot of conflicting and confusing legislation around fireproofing and roofing materials, there does not seem to be much legislation as to furniture or extra external elements that may provide a fire risk. The European standards and classes for roofing are mostly aimed at the construction items used in the actual roof, the waterproofing, concrete, drainage crates etc., not what sits on the roof. However, items such as fire breaks should be respected, and the plant choice given careful thought. Timber is acceptable on rooftop gardens, as seen in our other insight. Although architects should be careful that the firebreaks could be breached by any timber seating.
Our planters and furniture can help architects to make their roof-top gardens compliant. Small design tweaks can mean that your garden can be completely compliant without any spec or cost sacrifices.