EXTERNAL ENVELOPE Fireproofing green roofs
Julian Thurbin of modular green roof solutions supplier Wallbarn discusses the issues around ensuring fire performance of ‘living’ roofs and how to achieve compliance
key consideration for architects working on green roof projects has always been the load-bearing capability of the structure to be ‘greened.’ Once structural integrity is confirmed, it’s been a question of finalising the green roof system or supplier most appropriate for the project. This means choosing intensive or extensive, traditional roll-out, or the more modern approach of prefabricated modular solutions. However, there is a third consideration that demands examination – green roofs’ fire performance. Evaluating this has become increasingly important in the post- Grenfell years as the fire safety of buildings, their components, assembly, construction methods and management take centre stage. Well-designed, correctly installed and maintained green roofs can resist the spread of flame. To assist designers in achieving this, the Government has published two key documents: Approved Document B (ADB) and DCLG document ‘Fire Performance of Green Roofs and Walls’. Good practice supports these being considered in conjunction with the 2021 GRO Code published by the Green Roof Organisation.
A Regulations
ADB is the main authority and has been updated twice post-Grenfell to reflect recommendations from the Hackitt Report. It is the basis for all fire safety compliance and actions, and details the minimum legal requirements and guidance on how to meet them. The amended document states that a roof system must achieve a European classification rating of
BROOF(t4) when tested to CEN/TS 1187:2012 Test 4 Test Methods For External Fire Exposure to Roofs. The test must be carried out under BS EN 13501- 5:2016 Fire classification of construction products and building elements. In practice this means physical fire tests of the whole roof system to
demonstrate BROOF(t4) is achieved. Self-declarations, adaptations and
interpretations are not acceptable. Critically, BRE test reports P110472- 1001 Issue 2, P110472-1002 Issue 2 and P110472-1003 Issue 1 can no longer be relied upon to prove compliance with the legal requirements of Approved Document B. Stakeholders must demonstrate that the whole “as installed” roof system has a valid fire certificate.
ADB states that a test report to BS EN 13501-5:2016 for the exact construction is key. So if the insulation thickness is changed, the membrane switched or the depth or elements of the substrate/growing medium altered, then the fire certificate may be invalidated. This would mean
compliance with BROOF(t4) requiring possibly thousands of different physical fire tests to take into account the many different scenarios of a green roof build-up. This is as much an issue for roll-out systems as modular solutions – which are supplied with all elements of a green roof contained within factory assembled trays, removing the element of installer error and creating a standardised product with no variation – because there remains the potential for insulation and membrane specifications to be changed. However, ADB offers a solution via ‘EXAP reports.’
EXAP reports
These state that the test results for the product – tested in accordance with CEN/TS 1187:2012 test method 4 – have an extended application (EXAP) and can be used in a larger range of applications. This extended application is carried out in conformity to CEN/TS 16459:2019 and the application document contains extrapolation rules relevant to the test method and performance of the product. In short it enables the physical test data to be used in more applications than just the physical test.
Designers should be looking for green roof systems that have passed physical fire
tests of one hour, achieving BROOF(t4) and gaining the EXAP Report, meaning their fire classification allows them to be used as
75
Well-designed, correctly installed and maintained green roofs can resist the spread of flame
ADF FEBRUARY 2022
WWW.ARCHITECTSDATAFILE.CO.UK
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104 |
Page 105 |
Page 106 |
Page 107 |
Page 108
