A2 Rated Cladding – Why it’s still certified non-combustible?

 

How does the combustible ban view A2 rated cladding?

In simple terms, the recent changes to government guidance have banned the use of combustible materials in external cladding used in the construction of high-rise residential buildings. This detail is noted in Section I of the amendments to the Building Regulations. As of January 2019, any new structure that has one or more storeys at 18-metres above ground level and also features residential dwellings use A1 or A2 rated cladding. Student halls of residence, care homes, apartment buildings, hospitals and private schools are also included in the amendment, in addition to certain exterior fixtures, a prime example being balconies.

As well as new building structures, all existing buildings taller than 18-metres in height that are being refurbished or converted to residential use, will be required to meet the same requirements of a minimum A2 rated cladding product or alternatively will need to be stripped and replaced to a compliant standard.

What is the difference between A1 and A2 rated cladding classifications?

BS EN 13501 sets clearly defined thresholds for combustion performance, which involves testing to both EN ISO 1716 and EN ISO 1182 standards. One of these thresholds is a maximum heat of combustion of 2MJ/kg.

An A2 rated cladding panel has a higher combustibility and can sustain flame for no more than 20 seconds, it must achieve a threshold of maximum 3mj/kg heat of combustion. In contrast, A1 has a lower combustibility and no sustained flaming when tested, to achieve the A1 threshold, it must achieve a maximum 2mj/kg heat of combustion. Undeniably, these are very fine margins.

However, it’s also important to consider that a product can be certified as A2 even if it gives off an unlimited amount of smoke and unlimited flaming particles/droplets, for this reason the smoke and droplet ratings are also graded, with A2-s1,d0 achieving the best performance in both categories. Furthermore, it is a fact that smoke is the most common cause of deaths in fires in the UK and that flaming particles/droplets will tend to initiate new fires away from the original point of ignition. For these reasons, when consulted during the government enquiry, RIBA notably recommended that the combustibility ban should have restricted to A1 classifications only.

Typical A2 rated cladding materials

Material                                          Coating                                  EN13501-1 Rating

Solid Aluminium                             PPC                                       A2,s1,d0

Aluminium Composite                    PVDF                                    A2,s1-d0

Mineral Boards                              Liquid Paint                            A2,s1-d0

Fibre Cement Panels                    Liquid Paint                            A2,s1-d0

Reconstituted Stone                     None                                      A2,s1-d0

What else can affect EN13501-1 classification?

When specifying an A2 rated cladding system, using mechanical fixing methods such as rivets or self-drilling fixings, rather than adhesives, is a robust method to attach panels that will not negatively affect the fire rating of the overall construction.

Solid metals, such as aluminium, without additional bonded stiffening mechanisms – will either be rated non-combustible, A1, if anodised, or will typically be of limited combustibility, A2, if a powder coating is applied. If stiffening angles are required to achieve rigidity, it is possible to use welding fabrication techniques for attachment without compromising the fire rating. However, if used, structural tapes and adhesives are also required to meet the requirements of EN13501-1 so should have a maximum heat of combustion of less than <3.0MJ.kg.

When considering coatings, special attention should be taken to ensure the thickness of any organic coating is consistently maintained within the scope of classification. For architectural powder coatings, most major powder manufacturers stipulate that a minimum coating thickness of 60 microns is needed for the to ensure their durability to issue a warranty. If the coating applied falls below the minimum thickness, it’s possible to ‘improve’ the fire classification but with considerable compromise. Conversely, if powder coatings are applied at a thickness that exceeds the classified figure, there is a significant risk that what should be an A2 rated cladding panel, would actually have a higher heat of combustion value than stated. It’s crucial to carefully consider these details when reviewing the testing and classification documents provided by product manufacturers.

Which Ash & Lacy products and systems are compliant?

For the construction industry, Ash & Lacy products and systems are regularly tested by independent UKAS accredited organisations such as the Centre for Window & Cladding Technology (CWCT) and Warringtonfire and Lucideon, and accredited by globally recognised certifying bodies such as the British Board of Agreement.

Our rainscreen cladding systems have all been classified to the latest EN13501-1 standards, achieving a minimum of A2, s1-d0, ensuring compliance, safety, and peace of mind.

A summary of our range of classified systems can be viewed in full here – https://www.ashandlacy.com/testing-certifications/