The Grenfell Tower disaster was a tragic event that should never have occurred. The subsequent changes in construction regulations have affected all developments like it, roof spaces are no exception. Despite smaller fires prompting a need for building regulation changes, critical issues highlighted in a 2016 fire safety assessment of the building remained largely unaddressed even months later.
While roof gardens and spaces have gained popularity both before and after the disaster, the incident has rightfully made architects and builders more cautious about the fire resistance of materials placed at rooftop levels.
The Building (Amendment) Regulations 2018
It’s essential to note that the changes to building regulations following the Grenfell tragedy primarily pertain to cladding materials and not external furniture. The rapid spread of the fire at Grenfell was due to highly combustible aluminium polyethene cladding, leading to regulatory changes focused on cladding materials rather than outdoor furniture.
However, it would be irresponsible to ignore the fire risk on rooftops entirely. Therefore, we will assess various furniture and planter edging materials individually to determine their suitability from a fire risk perspective.
European Fire Classifications
Before we delve into the materials, it’s helpful to understand Euroclass fire ratings. Unlike time-based ratings, Euroclass focuses on the release of smoke and flaming particles. These ratings apply to all materials, and we’ve summarized them in the table below:
Timber on Roof Spaces
While untreated timber is prohibited for use as cladding on residential buildings above 30 meters, it is permitted for external furniture on rooftops. However, since timber is combustible, it requires careful consideration.
Various methods, such as treating timber with a fire-retardant formula, can enhance its fire resistance. Untreated timber has a Euroclass D rating, which can be improved to C or B with treatment.
Glass Reinforced Plastic on Roof Spaces (GRP)/Fiberglass/Composite Plastics
GRP, made from glass fiber strands resin-coated and molded into shape, is highly flammable and releases toxic black smoke when exposed to flames. Therefore, it is not recommended for use at roof level.
Steel on Roof Spaces (Mild Steel, Corten, and Powder Coated)
Steel is an ideal material for rooftop use. Nearly all types of steel have Euroclass A1 or A2 ratings, as they are non-combustible and heat resistant. Moreover, steel provides fire isolation, preventing the spread of flames in the event of a fire.
Lessons Learned Following Grenfell
The Grenfell tragedy underscored the importance of prioritizing fire safety. It highlighted the risks associated with poorly designed roof terraces and the dangers of cost-driven decisions. For example, non-combustible cladding specified for Grenfell was later changed to combustible cladding due to cost considerations.
We recommend the use of a combination of steel planters and wooden seating on roof terraces. This approach offers strong fire resistance, especially if the timber is treated with a fire-resistant formula and placed closely together. Timber’s natural appeal also helps maintain the green essence of roof gardens.