Since the dreadful tragedy at Grenfell Tower on June 14th 2017, over three years ago, there have been endless debates about the pros and cons of the different types of cladding currently available and the best options for removing and replacing the existing cladding that has been shown not to meet Building Regulations or not to be fire resistant.
For the many High Rise Residential Buildings (HRRBs) with suspect cladding there is the question of ‘who is going to foot the bill?’ Many of these have complex ownership and management structures, meaning it is difficult and often inequitable to apportion the enormous costs involved. Some owners of the apartments now find that the value of their homes has been evaluated at zero primarily due to structural safety flaws and fears.
Cladding became popular in the 1980s as it served a dual-purpose; it provided both weather resistance and thermal insulation. As time progressed more modern materials were used for the cladding but with little or no thought to fire safety. Instead it was prioritising the aesthetically pleasing value to the buildings in contrast to the dull, yet fire safe, concrete structures they were protecting.
A cavity between the wall and the cladding was designed to prevent the buildup of moisture or condensation and allow its controlled egress from the building, thereby preventing the steel reinforcing bars within the concrete walls from oxidation. As has sadly been witnessed in many recent fire tragedies, this cavity has provided the perfect route for smoke and heat to travel undetected horizontally and laterally around the building. Flames and heat intensify in the ‘chimney-like’ cavity and the integrity of the fire resistant qualities of the cladding, insulations and installations are severely tested. Even the most generally recognised fire resistant cladding material will produce toxic smoke at the high temperatures attained.
Furthermore this ‘chimney-like’ effect propels the heat and flames upwards towards the windows or doors immediately above the compartment of the fire’s origin, again aiding the fire spread. So this has to ask the question, ‘will replacing the existing cladding provide an absolute solution to the problem?’ If there remains the potential risk of smoke (Lakanal House) or both smoke and heat (Grenfell Tower) breaching into the cavities behind the cladding then the answer surely has to be ‘No!’ We aren’t breaking new ground here, this has been understood by everyone involved in construction; architects, surveyors, construction companies and Building Control – the facts and regulations have always been in place.
It is not only the cavities in between the cladding and the outer wall that are routes through which heat and flames can rapidly spread. Many buildings’ external walls have two ‘skins’, an inner and an outer, in between which is a narrow cavity. In fact there have been many recent incidents of buildings, especially hotels, being totally destroyed by fires that have spread quickly through these cavities, allowing heat to pass through to the vaulted lofts, causing eventual failure of structural integrity
Buildings that have both types of cavities are at greatest risk in a fire incident.
However, through planning and a calculated design we can manage this risk ensuring that these cavities are protected from ingress by smoke and heat. Ensuring that the cladding is protected from being compromised is a permanent managed solution for all buildings most at risk (more on this later).
Traditional Air and Boiler Vents (cladded or brick and block construction)
Many buildings, not just the HRRBs but buildings of all height and dimensions, have these vents penetrating through the integrity of the cladding and the cavities. Historically, but also through bad practice, the linings of these vents often have no fire resistance as many lining materials currently being used have absolutely zero fire rating. The scale of the problem is alarming. A compartment fire will eventually breach through the lining of this intermediate cavity with little or no protection in place.
A simple A1 fire-rated sleeve solves this dilemma. Installing the sleeve into the wall and beyond the cladding, then threading the vent from the boiler or extractor fan through the sleeve will protect the cavities and the cladding in a fire incident.
Window and Door Aperture Closers
The same strategy applies here. A window frame provides the perfect barrier to protect the wall’s cavities from ingress by smoke, heat or flames in a fire incident. All windows should have an A1 fire-rated pod into which the window frame is housed. An A1 fire-rated deflector, extending outward from the pod’s upper edge and beyond the cladding will lower the temperature of the heat that the compartment fire radiates to the cladding material.
The window pod, with or without the deflector, is designed with a drip tray to remove any buildup of moisture from within the cavities. Demonstrations of these pods, witnessed by fire industry professionals, social housing organisations and NHS Procurement teams, are available to view. Contact the author for more information.
As well as buildings with cladding, the window pods and sleeves are also very appropriate for timber-framed and modular buildings, constructed on or off-site. Including these in the manufacturing process delivers a compliant engineered solution and ensures that the cavities are properly protected.
The removal of the smoke and heat from a fire compartment and away from the cladding will have the following benefits:
1. It has a positive impact on the integrity of the building’s external structure. The extraction of the smoke removes the build up of heat and hot smoke and disrupts the physical elements of a ‘back draught’, a major operational risk for firefighters.
2. It will extend tenability in surrounding rooms compartments or apartments.
3. By extending visibility for locating the exit route from the building, it will allow a calmer and more orderly escape to safety.
4. It will assist the attending emergency services in dealing with the fire. The improved visibility will make it easier for them to identify the seat of the fire and its subsequent spread.
The Fire Safety Bill currently working its way through Parliament is designed to improve the safety of people in their homes, and we applaud this. Yet it still focuses on HRRBs and in January this year reduced the classification of these from 18ms to 11ms in height. Earlier in this Article reference was made to the protection of all the cavities and penetrations as a robust solution for ‘all buildings’. Fire Safety should apply to buildings of all sizes and compositions from the basement up to roof level. In addition it should apply throughout the lifespan of the building, I.e. from design, to build, occupancy and then eventual demolition!
For more information, go to www.ashfire.co.uk
About the Author
Paul Evans is a Smoke Control Consultant, Surveyor and Authorising Engineer for Ashev Limited, the manufacturer and distributor of A1 fire-rated window pods and sleeves.
