Learn more about the current fire safety challenges of designing ventilated façade and how we can help you in early stages of your project
What are the rainscreen façade requirements regarding fire safety currently in UK?
Everyone is aware of the Grenfell tragedy that served as a wake-up call to everyone and ultimately shaped our business. This tragedy put in motion a nationwide drive for change in the façade business, firestopping, code change and most importantly the mindset of everyone involved in the construction process to remind us all that safety must be our highest priority.
Façade is not a structural part of the building. It’s substructure is usually not part of the initial design process even though it has a major impact on the overall performance of the building. (e.g. usable space, sound resistance, thermal performance and more). Requirements can be confusing, contradicting and hard to navigate. So in the case of ventilated façade, they are often just imposed and passed down to contractor/fabricator to design.
If we look at the mandatory requirements in the UK for passive fire safety, rainscreen façade, the key document to follow is “Fire safety: Approved document B” (Publicly available here: https://www.gov.uk/government/publications/fire-safety-approved-document-b) This is the main document with all the fire safety related requirements in England. Below is the first general requirement that relates to façade.
General requirement for fire safety of external walls in Approved Document B 2020 edition. Please note that information here is based on May 2021 edition and this document can change!
Further on in the document we find two main sections related to rainscreen ventilated façade:
B3 Use of fire cavity barriers - section 8
Document B states where there are cavity barriers mandatory (openings, compartments) and their fire resistance (E30, I15). They are critical for the whole concept of compartmentalisation and containment of possible fire. Hilti offers fire cavity barriers both for ventilated or non-ventilated facades be they vertical or horizontal. All are tested according to BS 47620 and meet the code requirements.
Fire cavity barriers are part of Hilti portfolio and are included in our design services.
B4 External fire spread – is another chapter that defines, requirements for usage of combustible materials in façade structure, based on the height of the building and purpose. Depending on this, there are 3 possible ways to certify and ensure that façade is safe.
1. Façade is completely made from non-combustible parts (substructure, cladding, insulation all A1/A2) and thus the façade as a whole is considered non-combustible. Mandatory above 18m height. Exceptions exist in B4, Regulation 7 paragraph 3, see below for more info.
2. Façade contains some combustible parts and in order to meet requirements you must verify with document B if this can be used in relation to height and purpose of building on your project. For example, exceptions for buildings below 18m. (More info in Approved Document B)
3. Large scale test according to BS 8414 Fire performance of external cladding systems with classification according to BR135. Real-life large-scale testing done by independent 3rd party is the most objective way to determine fire safety performance of a system, however this is obviously an expensive and time-consuming option.
How is each Hilti ventilated façade system certified in relation to fire safety?
Hilti Eurofox façade systems are sold across Europe and have to meet varying local codes and requirements. Rainscreen facades and facades in general don’t have a harmonised European code yet, so Eurofox must comply with requirements in each market country separately. This gives Hilti a robust advantage in testing. Below you can find a list of all the Hilti Eurofox systems and description of how each is verified for passive fire safety, so it can be used even on high rise buildings above 18m where requirements are most strict.
Above paragraph 2 part B4 requirements for usage of non-combustible materials in façade structure. Approved Document B 2020.
Paragraph 3 exceptions to paragraph 2. See part (i) for thermal breaking materials.
This certificate is freely available and valid throughout Europe. Link here.
In terms of fire safety according to Approved document B, it still falls under the exemptions listed above but taking engineering judgement into account, Hilti did several large-scale voluntary tests across Europe to determine fire performance of Fox T as part of whole system.
For usage above 18m non-combustible insulation with non-combustible cladding is mandatory. Thermal break of Fox-T must be at least 10mm inside the insulation.
How was testing for Hilti Fox T done?
Right now, there is no harmonised European-wide code for large scale façade testing. In UK it follows code BS 8414 Fire performance of external cladding systems. Similar codes exist across Europe and future harmonised EN code should come from the UK BS and German DIN variant.
Hilti tested Fox-T according to BS 8414 two times, part 1 concrete and masonry wall and part 2 steel structure wall -SFS, once in 2017 with BRE and once in 2019 with FPA. Both times the system passed the tests and proved that it can be used in buildings above 18m height safely.
Large scale model prepared for the test according to BS 8414.
Outside of the UK Hilti also performed following large-scale fire tests of Fox-T:
- Two times in Austria (ÖNORM B 3800-5)
- Two times Germany (DIN 4102-20)
- Once in Poland (PN-B-02876)
In all those tests Fox-T was approved for use in high-rise buildings with appropriate insulation and cladding. All fire classifications are available at request from our engineers.
Hilti can assist you in optimising your project
Hilti has a dedicated division focusing on rainscreen substructure solutions. We work together with consultants, architects, fabricators and offer a network of trusted contractors. Our specialised engineers deliver optimised project calculations for your project.
Every substructure system and bracket has its purpose and is designed to meet the different needs and requirements of our customers.
Our comprehensive service offering includes:
- U value calculation and wall thickness optimisation
- Cooperation with multiple cladding suppliers
- Cooperation with insulation manufacturers
- Cooperation with installers
- Design and supply of façade substructure
- BIM design and support
- Façade fire safety consultation
- Structural design
- Sound resistance, calculation of Rw (C; Ctr)
If you have any questions related to the article or our rainscreen solutions and services, please post your question on Ask Hilti platform
To get in touch with our façade consultants to discuss your project specific needs, please send us an email
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This article is part of ongoing series dedicated to ventilated facades. Find more here.
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