Essential Metal Knowledge

How has Grenfell disaster changed the way we design roof spaces?

Introduction 

The Grenfell Tower disaster should never have happened.  Similar fires, albeit of a smaller scale, should have resulted in amendments to the building regulations.  A fire safety assessment of the building in 2016 discovered 40 serious issues and advised that they needed to be addressed within weeks.  4 months later, less than half had been addressed. 

Both before the disaster and after, roof gardens have continued to rise in popularity.  Its easy to see why – they offer a private secluded green space above the bustle of the city streets below.  Although Grenfell did not have a roof garden, the disaster and subsequent legislation changes have rightly made specifiers more cautious about the fire resistant properties of materials placed at roof level. 

This article will examine if, and how, these new building regulations relate to external furniture, such as planters and seating placed at roof level in roof gardens and terraces. 

The Building (Amendment) Regulations 2018 

The changes to the building regulations since Grenfell do not apply to external furniture.  As most readers would be aware, the reason the fire spread so quickly at Grenfell was because the aluminium polyethylene cladding was highly combustible.  Therefore, most regulation changes apply to cladding, not to external furniture. 

Although there is no regulation that directly affects rooftop furniture material, it is irresponsible to disregard the fire risk present at roof level.  Therefore, we will review each furniture and planter edging material individually and examine how suitable they are for rooftop terraces from a fire risk perspective.  

European Fire Classifications 

Before reviewing the materials, it is useful to understand about the Euroclass fire ratings.  With fire protection ratings, many people still use the Class 0, Class 1 and Class 2 system.  This is the old British Standard system and has been since replaced with the Euroclass system.  The Euroclass system was introduced to harmonise fire regulations which were becoming increasingly hard to interpret.  The Euroclass system is not time rated and does not offer 30, 60 or 90 minute fire resistance – instead it focuses on the release of smoke and flaming particles. 

These ratings apply to all materials.  No timber can meet Euroclass A1 or A2 regulations.  We have summarised the classifications in the table below: 

Euroclass Euroclass Definition British Standard (where applicable) 
A1 Non-Combustible Materials  
A2  
Combustible Materials: Very limited contribution to fire Class 0 
Combustible Materials: Limited contribution to fire Class 1 
  Class 2 
  Class 3 
Combustible Materials: Medium contribution to fire  
Combustible Materials: High contribution to fire  
Easily Flammable  

Timber 

Timber is sometimes perceived to be unsuitable for use on roof terraces.  This is not true – untreated timber is illegal for use as cladding on residential buildings above 30m but used as external furniture it is allowed.   

Despite this, timber is combustible and therefore, care must be taken when specifying it.  There are several methods that can be implemented to improve the fire resistance of timber – read our blog here for full details.  One of the most common methods is to treat the timber with a fire-retardant formula – untreated timber has a Euroclass D rating, with treatment this can improve to C or B. 

Glass Reinforced Plastic (GRP)/Fibreglass/Composite Plastics 

All composites are formed from a combination from two or more materials, like copper or steel metal alloys.  Therefore, combinations can be created to give an optimum blend of characteristics for the desired purpose of the material.  For GRP Planter tubs, this may be a combination of high strength, limited maintenance requirements and high resistance to corrosion.  All GRP’s are made from glass fibre strands which are resin coated and moulded into shape. 

Although it can be treated with a fire-retardant formula, GRP is even more flammable than timber.  Even worse, when exposed to flame it releases highly toxic, black smoke.  This is not only hazardous to the environment but also to people.  Therefore, it is not advised to use GRP or other composite plastics at roof level. 

Steel (Mild Steel, Corten and Powder Coated) 

Steel is the best material to use at roof level.  Barring exceptional cases, all steel has a Euroclass A1 or A2 rating.  It is non-combustible and heat resistant. 

The other advantage that steel offers is fire isolation.  Imagine a large square planter with integrated timber seating.  If a fire started on one of the benches, it would not be allowed to spread as the steel would keep the flames within that bench area. 

Lessons learnt following Grenfell 

Grenfell taught us to take fire safety more seriously.  At Grenfell, the main problem was the external cladding.   It also highlighted the danger that roof terraces can present if poorly designed.  One lesson that applies to all areas of a building, which has subsequently been highlighted in government reviews, is that the culture of continuous value engineering can adversely impact safety properties of buildings.  A few years before the Grenfell fire, the tower was refurbished, and new cladding was installed.  Originally non-combustible cladding was specified but it was revised to combustible cladding because the price tag was much smaller. 

Recommendation 

We recommend that a combination of steel planters and wooden seating is used on roof terraces.  This will offer good fire resistance, especially if the timber is treated with a fire-resistant formula and is placed closely together (read more about how to reduce the fire risk of timber furniture here).  As timber is a natural material, it will also help roof gardens maintain their valued status as a green enclave. 

Sources 

https://en.wikipedia.org/wiki/Grenfell_Tower_fire

https://gripclad.co.uk/useful-information/what-is-grp/

https://www.fibreglassdirect.co.uk/blog/post/why-grp

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