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External Wall Insulation
UK Fire Regulations

When it comes to EWI and fire regulations, the classification system defined in BS EN 13501-1 is the primary recognised standard in the construction industry as a whole and applies to external wall insulations systems.

The process for classification under this standard involves a combination of up to five rigorous tests designed to assess each product on a range of characteristics, including combustibility, heat levels, flame spread and smoke release. Once tested, the product receives an official classification of its Euroclass fire rating.

You can purchase a full copy of BS EN 13501-1 – Fire classification using data from reaction to fire tests.

Understanding Fire Classifications Of EWI Systems

It’s important to note that each individual component incorporated within an external wall insulation system is fire tested in its own right. The fire classification of an EWI system is therefore the sum of the different components.


The combustible nature of an EWI system is represented by a letter from A (plus a 1 or 2) to F.

A1 is non-combustible, A2 has very limited combustibility whilst products rated B to F are increasingly contributory fire factors:

EWI And Fire Regulations


The S number in an EWI fire classification represents the quantity of smoke generated and the speed of emission / intensity. The are 3 levels: S1 being the best where there is a zero or very weak emission of smoke as a result of a fire down to S3 when a high intensity of smoke is generated:

EWI And Fire Regulations

Flaming Droplets

The chart above also shows the D rating which represents the production of flaming droplets by a component or system during a fire. d0 means non dripping with a sliding scale down to d2 which is high dripping.

EWI And Fire Regulations

The best fire classification possible for any EWI system is therefore represented by A1 S1 d0

This means A1 – non combustible, S1 weak or no smoke and d0 no flaming droplets. However, any European Fire Classification rating of A2-s3, d2 or better is officially deemed as non-combustible.

As with any regulation these are minimum standards to be achieved. But, when it comes to fire, we always encourage you to think the safer the better in every case!

How Fire Safe Are EWI Systems

Most quality EPS EWI systems have, at very least, a classification of B-s3, d2 and are therefore classed as fire retardant. This means they have been manufactured to achieve a very low combustion level which has been approved by an accredited fire classifications expert and deemed safe and fit for purpose.

Mineral fibre insulation is A1 rated (non-combustible) but it stands to reason that every single other individual component within a mineral fibre EWI system would also need to be A1 rated in order that the system be classed A1 as a whole. For that reason any system achieving​ A2 or better is classed as non-combustible and can, hence, be specified on high rise buildings. There are many INCA member systems acheiving such high ratings of A2-s1, d0.

Fire classifications will clearly be stated by all INCA system designer members in respect of each of their individually specified external wall insulation systems. Find An INCA Member >.

External Wall Insulation
All You Need To Know