How to make Rooftop Gardens compliant with Fire Safety Regulations
Rooftop gardens are becoming not only a ‘nice to have’ but an urban necessity. In increasingly densely populated cities where green spaces are becoming fewer and farther between, rooftop gardens make the most of what would be ‘dead’ space. They can help to clean the air, cool the building, provide nourishment and shelter for wildlife, and even improve mental health. That’s why rooftop gardens with planters and seating are important considerations for today’s urban architects.
However, there is one very important aspect to take into account: building regulations.
Building regulations for rooftop gardens
In 2019, two years after the devastating Grenfell Tower fire, long-overdue amendments were made to UK Building Regulations. The new changes were called ‘Fire Safety Approved Document B’. And in addition to banning combustible cladding on high-rise buildings over 18m in height, new regulations relating to flat roof safety were introduced.
Section B4 of the document covers the regulations in full. However, as a brief summary, the document says that “the roof of the building shall adequately resist the spread of fire over the roof and from one building to another.” This means that roofs must:
- Feature soil or soil-like material that is at least 30mm deep
- Only use soil or soil-like material if it contains less than 20% organic matter
- Include a 1m wide fire break at 40m intervals (made from gravel or paving slab)
- Have gravel or shingle laid in strips around all penetrating structures
The regulations are based on the European Standard BS EN 13501-5 for fire performance classification procedures for roofs and roof coverings. Under this standard, roofs are given a rating – BROOF(t4), CROOF (t4), DROOF (t4), EROOF (t4), and FROOF (t4) based on their overall performance:
| European class | Minimum distance from any point on relevant boundary (England) | Minimum distance from any point on relevant boundary (Scotland) |
| BROOF(t4) | Unrestricted and can be used anywhere on the roof | Low Vulnerability (<6m) |
| CROOF(t4) | At least 6m of the boundary | Medium Vulnerability (6-24m) |
| DROOF(t4) | At least 6,12 or 20m of the boundary depending on the building type and use | Medium Vulnerability (6-24m) |
| EROOF(t4) | At least 6,12 or 20m of the boundary depending on the building type and use | High Vulnerability (>24m) |
| FROOF(t4) | At least 20m of the boundary depending on the building type and use | High Vulnerability (>24m) |
For maximum fire performance and safety, rooftop gardens should meet BROOF (t4) criteria. This is the highest possible European standard for roofs and roof coverings, as there is no AROOF rating.
What BS EN 13501-5 means for architects
For compliance with BROOF (t4) criteria, architects will naturally be looking to work with non-combustible materials. This includes materials such as stone, concrete, and steel. Even powder-coated steel is considered highly fire-resistant, as powder coatings don’t contain any volatile organic compounds (VOCs). So it’s natural to automatically consider cast stone planters, steel planters, or concrete seating for rooftop gardens. And these can certainly be attractive additions.
But what about combustible materials like timber? If the design calls for the aesthetic that natural wood can bring, can timber safely be used? If clients are eager to incorporate sustainable materials like FSC® -certified wood into their buildings, do they have the choice of incorporating wooden elements?
The answer, perhaps somewhat surprisingly, is ‘yes’. The new building regulations refer only to building elements that are considered to be a ‘specific attachment’. And while this includes balconies, cladding and decking, it does not include any external street furniture used on building rooftops. There are, therefore, no legal ramifications to using timber planters or seating for rooftop gardens.
Making responsible choices
Despite the rooftop regulations not applying to street furniture, it’s natural to want to design and create the safest spaces for visitors and residents. And while the fire risk to timber planters and seating is low, it’s important to remember that combustible materials can be set alight. The good news is that timber can be treated to reduce fire risk and make it a safer option for rooftops.
The first thing to consider is a fire-retardant treatment. This is a clear solution that is applied to wood to provide a flame-resistant coating. Untreated timber is often rated ‘D’ in the BS EN 13501-1 Euroclass system, marking it as having a ‘medium’ contribution to fire. However, a suitable treatment can transform this into a C rating – a ‘minor’ contribution – or even a B rating, which is a ‘limited’ contribution. Flame-retardant timber treatments may be applied by the supplier. They can also be applied after the fact, and there are numerous different treatment options available today.
Fire hazards are real. But they’re not a reason to feel deterred from developing stunning rooftop gardens that help to create a more sustainable planet.
