Grønne fasader; er de en estetisk brannfelle?
Mangelen på grøntareal spesielt i byene, har ført til en ny byggetrend med grønne fasader og gress og planter på tak. Dette er både et estetisk element, samtidig som grøntareal på selve byggene har en praktisk funksjon. Men er brannsikkerheten ivaretatt i like stor grad som estetikken?
Green facades or green walls are one of those construction trends that starts as both an aesthetic and a solution to a problem – the lack of green space. They were a natural follow-up to the use of green roofs, mostly as they are capable to provide larger areas of vegetation, in hopes of changing the face of concrete jungle-like cities. Sometimes referred to as living walls, green walls do not have enough guidance and legislations for their usage, which opens things up to speculation and lack of necessary management.
What are green facades?
These are intentionally vegetated facades which can be achieved through plants originating from the ground and supported through a trellis, or modular cells filled with substrates and planted. Either way, irrigation is provided at source (in the first instance from the ground, and in the second instance through an irrigation system to the cells).
What are their benefits?
They can have several benefits, besides looking aesthetically pleasing. They can provide great aid in reducing pollution levels in highly urban settings, as any other type of vegetation can. This can result in an enhanced air quality within the areas they are used. The buildings that support them can also directly benefit from that as the vegetation can filter the external air entering its air handling units for cooling and heating.
Another one of those benefits is thermal advantages, as green walls offer an applied construction cladding with a certain degree of solar shade and improved thermal performance. They can basically create centralized microclimates through the natural process of absorbing solar radiation and evaporation through the leaves. This can significantly contribute to cooling buildings in hotter climates. Moreover, the acoustic performance of those walls is highly credible in providing noise and sound reduction.
What about Fire Safety?
A ban on combustible materials used in facades was introduced in the UK in 2018 after the Grenfell tower disaster. A major concern would be that this ban would include green facades and other innovative products such as photovoltaic cells. The current testing system is clearly lacking and limited in scope. Hence, a more risk-based approach should be considered, especially for innovative materials and systems, and that includes green facades.
According to the Department for Communities and Local Government (DCLG) which specifies the guidance on how to use green roofs and green facades in the UK (and published on the gov.uk webpage), it is suggested that the type of system used within the green wall determines whether or not it would be deemed as fire safe. It is mentioned that growing mediums, except organic materials, are unlikely to promote fire spread. This is on the basis that for the wall to be kept alive and “green”, the irrigation levels should be maintained at all times, thus hindering fire spread. However, High Density Polyethylene (HDPE) plastics used for modular living wall systems have a high tendency of ignition.
As the level of testing on green facades is relatively minimal, the guidance we have at hand reflects that problem. Thus, considerations are more likely to be generic rather than detailed. Those considerations include increasing the non-combustible contents of the growing medium, decreasing the organic content, and making sure that sufficient irrigation levels are maintained to prevent the system from drying out. It is also recommended that fire breaks are used. These are mainly referred to as non-vegetated border zones that can stop or limit the progress of fire within the façade.
To limit the fire spread
Standard compliance documents are referred to, as a method of assessing the green facades as a regular external wall and deciding accordingly. This is usually applicable when trying to assess the likelihood, and consequences, of a façade fire spreading back into the building. In that case, the façade system would need to comply with requirements B2, B3, and B4 of the Building Regulations and Approved Document B. B2 relates to Internal Fire Spread (Linings), and in order to comply with it, the wall and ceiling lines should be able to meet a specific criteria that is set in Approved Document B. B3 relates to Internal Fire Spread (Structure), and in order to comply with it, adequate provisions would need to be put in place to prevent fire spreading through the façade from one floor to another and consequently through compartment floors. Fire stopping and cavity barriers are the main elements of hindering that fire spread.
B4 relates to External Fire Spread, and in order to comply with this requirement, fire spread along the green façade should be limited so that radiation does not cause fire spread to surrounding buildings. The materials used on the façade itself along with the boundary distance are both factors in this requirement.
Though green facades can be a great addition to any building, especially those within highly populated urban cities that lack the element of nature, the whole system needs to be studied carefully for both advantages and disadvantages before applying. As an architect, I’ve always known green facades as the aesthetic and functional element that provide a continuation of nature into the building. However, as a fire engineer, my concerns are definitely much higher. Until manufacturers are capable, and willing, to produce specific fire tests to each holistic system used rather than isolated parts, the systems’ fire performance remains to be a concern. The use of plastics in most of those systems will always be a major threat.
If we are to balance the pros and cons, In the United Kingdom, as well as other cool climates, the thermal cooling provided by those systems is not necessarily needed. This deems the thermal benefits of those facades as useless. However, the benefits they can provide in terms of the psychological connection of the humans with nature is quite high. Nevertheless, building owners would need to understand that such systems require regular maintenance and verification that all the components are working properly, especially when it comes to irrigation. Irrigation would be the main issue that could turn an eco-friendly and aesthetically pleasing façade into an accident waiting to happen.
Litt om journalisten:
Amani er en libanesisk arkitektingeniør med en spesiell interesse for fagfeltet sikkerhet. Hun har også en Mastergrad i brannsikkerhet fra Høgskulen på Vestlandet (HVL), som hun var ferdig med i 2020. Hun har siden begynnelsen av 2021 jobbet som Graduate Fire Engineer ved Arup UK, og skriver med brennende engasjement for Brennaktuelt.no på fritiden.
Fuller, D. (2015). The NBS guide to façade greening (Part Three). NBS. Retrieved from https://www.thenbs.com/knowledge/the-nbs-guide-to-facade-greening-part-three
Government, D. f. (2013). Fire Performance of Green Roofs and Walls. London: HMG. Retrieved from https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/230510/ 130819_SW3529R_-_Issue_3_-_Green_Roofs_and_Walls_Project_web_version_v3.pdf