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  • Writer's pictureGrace Rogers

Green Walls - Pearls and Pitfalls

Urban Greening Factor

Green Walls introduce much-needed greening to built-up spaces, soften the visual impact of a structure, and add an impressive vertical element to many planting schemes. Living Walls can also assist where greening is a planning requirement, as it is in any major development in London, where a high-quality landscape design is now a requirement.

For a scheme to be successful, a knowledge of their ecology and the Regulations surrounding them is essential.

Building Regulations for Green Walls

Recent Amendments to the Building Regulations Regulations were brought into force in 2022 specifying fire performance for external cladding—which includes Green Walls.

But it is worth noting the use of combustible materials in construction have been under increased scrutiny since the Grenfell Tower fire, and as a consequence, Green Walls now have limited applications. The Approved Document Part B (2019 as amended 2022), refers to 2013 guidance on Green Walls in Paragraph 10.7 of Volume 1 for Dwellings.

Green Walls and Fire Safety

The Amended Regulations indicate that for most buildings, external cladding needs a Fire Standard of “Class B-s3, d2 or better”.

  • “Class B” means that the cladding has limited combustibility;

  • “s3” means that substantial smoke is released; and

  • “d2” means that quite a lot of flaming droplets or particles are released under testing.

Fire Safety Tests have been carried out on plastic-based Green Wall systems with wet growing medium and moist plants (in test “BS EN 13501-1”), and these systems obtain a “Class B-s1,d0” or “Class B-s2,d0” rating.

  • “Class B” means that the cladding has limited combustibility;

  • “s1” means little or no smoke is released;

  • “s2” means that quite a lot of smoke is released; and

  • “d0” means that no flaming droplets or particles are released under testing.

This means Green Walls do have the requisite fire performance for most buildings.

However, for residential buildings which are 11 metres high or taller, "non-combustible" external cladding is now required. The definition for “non-combustible cladding” requires cladding to meet the standard “Class A2-s1, d0 or better” under testing.

  • "Class A” means that the cladding is non-combustible;

  • “s1” means little or no smoke is released; and

  • “d0” means that no flaming droplets or particles are released.

These ratings mean that because the plants and growing medium in any Green Wall are “somewhat combustible” and therefore not “Class A”, a Green Wall cannot now meet fire standards for a residential building 11 metres or more in height. (This applies to “all cladding”—not just that part of façade above the 11 metre threshold - see Building Regulations, Section 10.5).

Green Walls are Allowed for Most Buildings

A properly installed and maintained irrigation system is of vital importance in this respect: written evidence submitted by RISCAuthority to Parliament in 2022 suggests that without the protection of water in planting, green walls would obtain a Class C, D or E rating—which is something to be avoided if a Green Wall is going to succeed: the plants should be moist and the growing medium wet from a fire safety perspective. But there is more to Green Walls than fire safety:

Keeping Green Walls Successful

Many green walls have succeed and many have failed, particularly as baseline temperatures, and spikes in temperature in the United Kingdom have increased significantly in the last decade. Living walls can be specified appropriately in respect of their sustainability and their resilience. Resilience in the landscaping industry is now a priority, and in a changing climate, the ethos ‘right plant right place’ is now more relevant than ever. This knowledge-oriented approach reduces the impact on resources and the potential for loss of plants, and it increases the potential for thriving green spaces with biodiverse ecologies. The most hardy and commonly specified plants for living walls (e.g. Heuchera, Tiarella, Viola, ferns) would traditionally grow in damp woodland and prefer rich soil with an abundance of organic matter, which is found in the soil of the forest floor. The growing medium in a green wall system would lose nutrients in the first year, and over time, watering and root growth compacts the soils, making it more difficult for the plant to absorb water. These woodland plants, which naturally thrive in damp, nutrient-rich, locations, then become subject to dry, nutrient-poor soil after a short number of years, eventually making the green wall system a hostile environment for these plants unless they are correctly specified and maintained.

Ideally, plants in the right place should thrive with little input, in their natural environment; forming deep root systems that can find water without irrigation — or if irrigation is needed, using rain gardens that harvest excess storm water. Green Walls tend to need fairly heavy artificial irrigation to keep the plants alive; and the most sustainable way of ensuring this is with a roof drainage system designed into the building to harvest rainwater to irrigate the wall. The nature of a vertical garden is such that the soil is both shallow and free draining, potentially subject to drying from wind and subject to soil compaction, causing water run-off. So irrigation also has to be carefully arranged for a living wall to thrive. We would consider the position and orientation of a Green Wall: if it is in shade, even partial shade, it is most likely to require plants that tolerate dry shade. Site-specific conditions such as wind, temperature, and sun’s path across the wall will all determine what sort of system and what planting we would specify for a Living Wall.

For some expert advice,

Get in touch with Grace to discuss your own Green Wall.

Or for further reading on Green Walls, see:

  • Fire Safety Approved Document B (2019 edition incorporating 2020 and 2022 amendments) in The Building Regulations 2010 (available at: uploads/system/uploads/attachment_data/file/1124733/ Approved_Document_B__fire_safety__volume_1_- Dwellings_2019_edition_incorporating_2020_and_2022_amendments.pdf)

  • Written evidence submitted by RISCAuthority [EXA 038] (available at: https://

  • Planting Green Roofs and Living Walls by N Dunnett & N Kingsbury (Timber Press, 2004)

  • Resilient Garden Sustainable Gardening for a Changing Climate by T Massey & Royal Horticultural Society (Dorking Kindersley 2023)

  • Right Plant, Right Place: The Indespensible Guide to the Successful Garden by N Ferguson (Aura, 1984)

  • Green Walls by the Royal Horticultural Society (RHS, 2023)

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