What is cladding?

The term cladding refers to the outer skin applied to a high rise building to increase thermal energy efficiency or improve aesthetics, while not adversely affecting weather resistance. The cladding element is non-load bearing, which means it is not structurally integral to the building itself. 

Cladding can either be retrofitted to an existing building or incorporated into the design of a new building.

What are the different types of cladding?

There are many different types of cladding systems available, ranging from the traditional looking brickwork or rendered systems to more modern looking metallic rainscreen systems or curtain walls made from glass. Cladding systems can be complicated constructions with voids, breather membranes, cavity barriers etc. but the two main cladding materials are the thermal insulation and the front façade panel.

The thermal insulation is generally made from either a mineral (stone) wool or a foam, such as phenolic foam or PIR foam. Façade panels can be made from a wide variety of materials including wood, metal, brick or vinyl, and are often made from composite materials. Two types of composites which have been highlighted in the news are ACM and HPL.

ACM (aluminium composite material) façade panels are made up of two aluminium skins bonded to a non-aluminium core which can be highly combustible. This is the type of façade panel that was responsible for the rapid vertical fire spread during the Grenfell Tower fire in West London in 2017.

HPL (high pressure laminate) façade panels are a type of timber cladding made by pressurising layers of wood or paper fibres into a resin and then bonding them together using heat. This is the type of façade panel that was used on the University of Bolton student accommodation block that caught fire in 2019.

How is cladding dangerous?

A cladding system has the potential to spread fire to all of the occupied spaces in a building, bypassing all of its internal fire compartments. There are two main factors that can enable this:

Firstly, if the cladding system in question contains combustible materials, such as expanded polystyrene (EPS) or polyurethane (PUR), then exposing these materials to a flame can result in rapid fire spread on the outside of a building. This can occur through either a fire breaking out from one of the windows or doorways, through ventilation shafts, or from a fire that has occurred on the outside.

Secondly, rainscreen cladding systems also require an open cavity to allow the insulation to ‘breathe’ behind the weather resistant cladding panels. However, this is potentially dangerous in a fire, as it creates a chimney for the fire to spread vertically through the building.

Fire stopping measures are incorporated into nearly every cladding system but some are more effective than others. Many are made using mineral-based materials which are non-combustible and highly effective at slowing the spread of fire around the outside of the building. To allow the cavity to breathe, most cavity barriers on the market now incorporate an intumescent strip. This expands under the application of heat, which seals the cavity during a fire. When correctly applied, this dramatically slows the vertical spread of fire. This is called an open state cavity barrier.

Is cladding on every building?

No, cladding is not on every building. However, it is increasingly used on both new build high rises, and older concrete buildings that have been renovated. A building with cladding does not necessarily pose a threat to its occupants. Some materials are perfectly safe from a fire spread perspective, for example stone cladding systems using mineral wool, cement board, concrete panels etc. can be completely non-combustible with good fire resistance.

What do building regulations currently say about cladding?

The building regulations were amended in 2018 to implement a ban on combustible building materials on the outside walls of buildings that are taller than 18 metres and contain more than one dwelling.

This ban applies to residential housing tower blocks, hospitals, residential care homes, and student accommodation blocks. Fire risk assessments for high-rise tower blocks will also start to include the external walls of a building.

Should I get a fire test on my cladding?

That depends on what your cladding is made from. In most cases, records of the materials that have been used in the construction process are held by the building owners or construction contractor – these will give you an indication of whether or not your building is at risk. If this information is not available, you may need to have a sample of your cladding system tested to determine the materials it contains and whether or not there is a potential fire risk.

Find out more about the FPA’s BS 8414 Cladding Testing.