Fire Ratings Explained - A Complete Guide

Whether it be cladding, decking or fascia, many products in the building industry (especially those produced by top quality manufacturers) come with a fire rating; a classification that tells the user how resistant to fire that product is. As a customer, you may have seen some of these fire ratings such as A1, C, 1 as well as the term retardant and it may all seem quite confusing. Fear not, as in this helpful guide we aim to help you understand everything you need to know about fire ratings!

What does retardant mean?

The term retardant is used to describe a substance that makes the growth and spread of something slower. The degree to which this spread is slowed down or the measurement of how much it is slowed down by is known as retardancy. So, a fire retardant is a substance that slows down the spread of fire and there are many different levels of fire retardancy.

What are all of the fire ratings?

There are two main standards that materials and products are assessed under:

• BS 476-1 – Fire tests on building materials and structures.
• BS-EN 13501-1 – Fire classification of construction products and building elements.

Firstly, the BS 476-1 standard that measures the spread of flame along the surface of a product that is positioned vertically, there are five ratings:

• Class 0 - Protected against the spread of flames and the amount of heat that is released from the product is limited.
• Class 1 - Protected against the spread of flames.
• Classes 2 – 4 – These classes incrementally increase in the distance and speed measured that the flames travel across, with Class 4 having the fastest flame spread over the longest distance.

As for the BS-EN 13501-1 standard, there are a total of seven individual fire ratings that measure how combustible a product is and how much it would contribute to a fire, and they are as follows:

This information is all well and good for knowing which fire ratings exist, but let’s take a closer look at each rating.

Class 0

To meet a Class 0 rating, a product must not go through a single test, but meet a series of requirements. First, it must pass the test and achieve a Class 1 fire rating. It must also achieve an index of I < 12 and I1 < 6 from BS476 Pt 6 – Fire Propagation.

Class 1

Class 1 is the highest fire rating in the BS 476-1 standard, an example of a good class 1 rating would see flames spreading no further than 165mm from the start point over 10 minutes on a product. Our product ranges that feature a Class 1 fire rating include polycarbonate sheets, hygiene cladding, bathroom and kitchen cladding and our white, anthracite grey, black ash, golden oak and rosewood hollow soffit boards.

Classes 2-4

These classes incrementally increase in the distance and speed measured that the flames travel across, with Class 4 having the fastest flame spread over the longest distance. Our 18mm fascia and 9mm capping boards are class 2 fire rated.

Class A1 & A2

Products with a Class A1 or A2 fire rating have been put through the most stringent of tests against their heat levels, combustibility, flame spread and smoke release and have passed with flying colours. They are therefore classed as non-combustibles, meaning they won’t contribute to a fire. Only materials with a Class A fire rating can be used on high rise property (18 metres or above).

Examples of materials that would fall into this class are concrete, brick and stone.

What is the difference between Class A1 and A2 fire ratings?

The only difference between these two ratings is that although A2 has no contribution to fire, it may still produce smoke or flaming droplets. With A1 rated products there is no chance of this.

Class B

Class B rated products are defined as highly resistant to flame spread and having a very limited contribution to fires. They have a flame spread rating of between 26 and 75. As stated above, B rated materials should not be used on buildings that are over 18 metres high as this will violate fire regulations. Examples of class B materials are fire resistant MDF, some birch plywoods and wood wool cement.

Class C

Materials with a C rating have a flame spread rating of between 76 and 200 and are considered effective against medium fire exposure. Our mineral composite decking boards and trims hold a class C fire rating and some other examples of materials that feature a C fire rating are plywood, fibreboard and faster burning whole wood.

Class D

Class D certified materials are capable of resisting a small flame attack for a long period of time and have a flame spread rating of between 201 and 500. These products are also prone to thermal attack by a single burning item with limited heat release. Expanded or extruded polystyrene and foil faced Polyisocyanurate foam are examples of products that would typically be in this class.

Class E

Products under this class are capable of resisting a small flame attack for only a short period of time and have a flame spread rating of over 500. Class E materials include laminate faced Polyurethane Foam, sprayed Polyisocyanurate foam and vacuum pressed Wood fibre board.

Class F

Class F is defined as either products that have not been tested against fire regulations or have not met any of the requirements of Classes A1 – E and are therefore likely to be easily flammable.