Fire Rated Materials for External Wall Cladding
One thing I came across whilst looking at materials in the refurbishment of Student Accommodation (classed as a Relevant Building) was the need to ensure that materials were ‘Fire Rated’. There are essentially three factors that are checked in a laboratory in set test conditions. There’s combustibility, smoke generation and fire generation.
Here's an example of a product’s fire rating:
A1 – Combustibility
s1 – Smoke Generation
d0 – Fire Generation
Combustibility (or Fire Class)
These are rated from A to F. I think of them like the old school grading system when A is the best and F is a fail. You could even get an A+ at school and that’s the same here, there’s an A1 (the best) closely followed by A2. The new regulations state that A1 is preferred, but where these products can’t be purchased in time, then A2 is suitable. Naturally, double-check ADB and the Building Safety Act for further details.
Smoke Generation
This measurement is annotated as either s1, s2 or s3. A1 materials don’t get smoke generation as they’re non-combustible. These pertain to materials with a Fire Class of A2 to D. s1 is classed as smoke intensity levels absent or very little. s3 has a high volume of intensity. (note : smoke inhalation kills more people than the direct contact with the fire)
Fire Generation
This was a factor that increased the fire generation in the Grenfell fire of 2016. This factor measure the amount of burning droplets/particles generated during the first 10 minutes of exposure. These only affect Fire Classes of A2 to E.
Examples
Just looking at the Rockwool, Cool ‘n’ Comfort RL920 fire insulation, this has a ‘Fire Performance non combustibility of A1. As it’s A1, Smoke Generation and Fire Generation aren’t factored in.
We have another example of DuPont’s Tyvek FireCurb Housewrap with a Fire Rating of B-s1,d0.
Exemptions
There are exemptions to this type of testing (these are listed in the Building (Amendment) Regulations 2018 (ref : https://www.legislation.gov.uk/uksi/2018/1230/regulation/2/made ) :
cavity trays when used between two leaves of masonry;
any part of a roof (other than any part of a roof which falls within paragraph (iv) of regulation 2(6)) if that part is connected to an external wall;
door frames and doors;
electrical installations;
insulation and water proofing materials used below ground level;
intumescent and fire stopping materials where the inclusion of the materials is necessary to meet the requirements of Part B of Schedule 1;
membranes;
seals, gaskets, fixings, sealants and backer rods;
thermal break materials where the inclusion of the materials is necessary to meet the thermal bridging requirements of Part L of Schedule 1; or
window frames and glass.
Nutshell Summary
Any building over 18m and work done on the exterior of a building, such as the Cladding, and not on the list above, should have a Fire Rating of A2-S1,d0 or better
Fire safety is a crucial aspect of any building refurbishment, regardless of its purpose. Using fire-rated materials and installing fire detection and alarm systems are essential to ensure the safety of occupants. By assessing factors such as combustibility, smoke generation, and fire generation, we can create a safer living or working environment for everyone.
Terms & References:
Relevant Building : Any building above 18m above ground level, and which, contains one or more dwellings, contains an institution; or contains a room for residential purposes (excluding any room in a hostel, hotel or boarding house).
Above Ground Level : The measurement of the lowest ground level outside the building to the top of the floor surface of the storey.
Institution: residential areas, schools, care homes, hospitals, sheltered accommodation, student residences etc.
The Building (Amendment) Regulations (2018)
Approved Document B
BS EN 13501-1