Fire Rating for Exterior Cladding

Your home is more than just a house. Home is about spending time with family or friends, enjoying your leisure time or relaxing after a hard day at the office. For many, a home is a sanctuary, and the protection it offers – shelter from the elements – is a critical part of keeping you and your family safe.

After the tragic fire at Grenfell in 2017, choosing a cladding material that offers maximum fire resistance has become ever more important not just for homeowners, but for architects and builders too.

But just how does the current regulation work, and as a homeowner, how do you ensure the best fire resistance protection for your home and your family?

Many external cladding materials currently on the market carry a minimum classification of ’surface spread of flame’, designed to slow and control any spread of fire. However only a few materials provide the higher classifications of either limited combustibility or non-combustibility.

The fire rating classification for cladding material ranges from A1 to F in accordance with European Standards EN-13501-1. These are shown below:

A = Non-Combustible
B = Very limited contribution to fire
C = Limited contribution to fire
D = Medium contribution to fire
E = High contribution to fire
F = Highly flammable

Fire Rating: Fibre cement cladding vs. uPVC/Vinyl cladding

uPVC or Vinyl cladding

PVC/uPVC or vinyl cladding products usually have a fire rating of C or D, which means this type of cladding is combustible. For comparison, most untreated wood cladding products have a fire rating of D.

uPVC is composed of two building blocks, chlorine and ethylene from natural gas or petroleum. In other words, salt and oil. These raw materials are made into synthetic products called polymers, a form of plastic.

Due to the composition of PVC, being a plastic cladding material, it will melt and warp when exposed to fire. There are even extreme instances where uPVC cladding has melted from the reflection of the sun off Low-E glass windows. Although the spread of flames across the surface of uPVC might be limited, depending on the backing, PVC cladding will char and melt when exposed to fire. When PVC cladding burns, a chemical is realised called toxic dioxin, which is a hazard to the environment and humans.

Fibre Cement Cladding

Fibre cement cladding from James Hardie has a fire rating of A2, s1 d0, which is the highest possible fire rating for a coloured cladding board. This means that it is a non-combustible cladding, and will not ignite when exposed to direct flame or extreme heat, nor will it contribute fuel to a fire.

Read more about fire resistant cladding here.

New UK Legislation for Cladding

Last year the UK government introduced an amendment to The Building Regulations (Approved Document B: fire safety) regarding fire rating for cladding on buildings. This amendment now states that due to fire safety, all residential buildings now have to be built with A1 or A2-s1, d0 components in the external wall and cladding layer. This is at all heights.

You can read more about this here and here.

So what does this mean for building designers and contractors?

This means some very significant changes to the way we design and construct buildings. From a materials perspective, good quality high fire rated insulation is a must.

In addition, exterior cladding materials need to be selected with safety and non-combustibility in mind. Fibre cement and terracotta cladding will continue to increase in popularity due to their fire resistant properties, alongside some ACM products (aluminium composite materials) which will also comply. uPVC, HPL (high pressure laminate) and untreated wood will unfortunately not.