Managing risks with living walls

12 June 2023

Living walls, often referred to as green walls or vertical gardens look beautiful and are a visual way to indicate that a building is sustainable.

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Living walls can be achieved in a number of ways:

  • Climbing plants - growing directly against the wall or trained against a trellis. The plants can be rooted into the ground or in substrate-filled planters. Such systems are usually irrigated but can survive without irrigation if rooted into the ground.
  • Hydroponic green walls - usually constructed from plastic mesh, geotextiles, fabrics or horticultural mineral wool or combinations of materials fixed to supporting frames or boards. Plants grow without substrate or soil and rely on irrigation and nutrients added to the irrigation water.
  • Modular green walls - made from purpose-built HDPE (high-density polyethylene) modules, containing cells that are filled with growing medium and planted. Modules are fixed to a wall or frame and may be combined to cover large areas. Irrigation water is usually delivered to the top of each module via irrigation lines. Nutrients can be contained in the soil or added to the irrigation water supply.

Most living walls are constructed using bespoke carrier systems and the component parts can vary. For example, a system may use the rails which form part of a building's cladding, to support modular plant boxes. Other elements can include water-resistant backing layers, irrigation systems, drainage channels and of course, the growing medium and plants.

Fire risks with green walls

Like any cladding system, there will be a backing wall with insulation and the possibility of vertical voids through which a fire may spread. Even if the system has suitable cavity barriers installed, some components (including some types of growing medium) may be combustible and contribute to fire spread.

It is important to look at the whole wall build-up when considering the fire susceptibility of a living wall. Wherever possible, the backing wall, insulation and support systems should be of non-combustible material to limit the spread of fire as far as possible.

It’s clear from the number of new building specifications we see that contain green roofs or walls, that these building techniques are becoming more popular. The insurance industry has embraced the drive towards achieving Carbon Zero but there are concerns about the increased use of combustible materials in buildings and sustainability should not equal combustibility.

As an insurer, we would actively encourage you to involve your insurer in the planning stage for any new sustainability project. That way, we can work together to mitigate risks at the planning stage to achieve a modern sustainable building.