How liquid membranes are helping to unlock a more sustainable future

The UK government's 2030 net-zero target is no longer a distant aspiration - it's a rapidly approaching deadline. With just five years to ensure residential properties achieve an Energy Performance Certificate (EPC) of 'C' or higher, and commercial builds a 'B' or higher, the pressure on architects, property designers and developers is immense. This is not just about ticking boxes - it's about designing smarter, more energy-efficient buildings that actively contribute to a better planet.

This is where green roofs, together with the seamless protection of liquid membranes, can become a game-changer, particularly when combined with intelligent greywater recycling systems to create a circular water economy within a building. Liquid waterproofing membranes, unlike traditional sheet membranes which rely on seams and joins, are applied as a continuous, monolithic coating. This seamless characteristic is critical, especially for when designing an environment for a green roof.

Green roofs involve multiple layers of growing media, drainage and irrigation systems. Any vulnerability in the waterproofing layer can lead to catastrophic leaks. Liquid membranes provide a fully bonded barrier that eliminates weak points, ensuring protection against water ingress. This is especially vital for all systems designed to hold water, both blue and green roofs.

A blue roof is a flat roof designed specifically to manage stormwater runoff by temporarily storing water on its surface before slowly releasing it into the drainage system, preventing sudden surges and reducing flood risk. It's primarily engineered for water attenuation. A blue-green roof, on the other hand, combines this water attenuation capability with the ecological and aesthetic benefits of a green roof. It incorporates layers of vegetation and growing media on top of the water storage layer, effectively blending stormwater management with biodiversity, insulation and amenity space. While a blue roof's main purpose is water retention, a blue-green roof enhances this by integrating living elements that contribute to urban greening and climate resilience.

With both types of systems, roofing professionals are aware of potential movement in buildings due to changes in a roof system’s weight, caused by the fluctuating levels of water held within the blue and green roof elements at any one time. This causes a live load that the building needs to bear. Therefore, seamless liquid applied waterproofing systems with high levels of elasticity are ideal to withstand such structural movement.  This is why many modern cold-applied liquid systems, such as those provided by Proteus Waterproofing, are BBA certified to last for the life of the building on which they are installed, even under the constant presence of water and root systems.

The green roof revolution
Green roofs are no longer perceived as a niche, eco-luxury item. They are becoming a mainstream high-performance building component, actively contributing to urban resilience and building efficiency. One of the most significant advantages of green roofs, particularly in urban areas prone to flash flooding, is their capacity for stormwater attenuation. The substrate and vegetation layers act like a giant sponge, absorbing vast quantities of rainfall and slowly releasing it, or allowing it to evaporate.

Studies show that green roofs can typically retain between 70-80% of rainfall runoff in summer months. Even during heavier downpours, they significantly attenuate peak flow rates, reducing pressure on overstretched sewer systems. For example, research in Plymouth showed green roofs could reduce runoff by up to 15% via evapotranspiration. This directly translates to reduced flood risk and can even negate the need for costly underground attenuation tanks or further adaptations to conventional drainage systems.

Green roofs also provide a natural layer of insulation, keeping buildings cooler in summer and warmer in winter. The evapotranspiration from plants, and shading provided by vegetation, can significantly reduce surface temperatures on the roof. A conventional bitumen roof surface can exceed 50°C on a sunny summer day, leading to significant heat gain inside the property. A green roof can reduce this lowering internal building temperatures. 
Furthermore, in increasingly concreted urban environments, green roofs provide vital habitats for birds, insects and pollinators. They can transform barren rooftops into thriving ecosystems, supporting urban biodiversity and contributing to a healthier urban environment. Green roof systems can create biodiverse spaces, from wildflower meadows to more structured planting, providing ecological value.

Greywater reuse and non-potable storage
However, the real magic happens when the water management capabilities of green roofs are integrated with a building's broader water strategy, particularly through greywater recycling. Greywater is wastewater from baths, showers, washbasins and washing machines – essentially, any domestic wastewater that does not contain human waste. This non-potable water, often accounting for over 50% of a household’s daily water consumption, is a valuable resource often flushed away.

Liquid waterproofing membranes are ideal for lining non-potable water storage tanks, whether they are integrated into the green roof system (as part of a "blue-green roof" design that temporarily stores rainwater) or within the building's basement. Their seamless, fully adhered nature ensures a leak-proof containment vessel for harvested rainwater or treated greywater. Such membranes can form linings for underground or rooftop tanks designed for large volumes of non-potable water, ensuring no seepage.
Green roofs naturally harvest rainwater. This collected water, already filtered to some extent by the substrate, can be channelled into a storage tank for later reuse. A well-sized greywater recycling unit can save around a third of a household's potable water.

A good example of this is the Mariner's Quay development in South Wales, which incorporates both rainwater harvesting and greywater recycling, and saves an estimated 33 litres of potable water per person per day. Industry estimates suggest that if just 10% of the UK population installed a greywater recycling system, it could cut average water consumption from 150 litres per person per day to 145 lpd, with potential for further reductions over time.

While the initial investment for sustainable systems like green roofs and greywater recycling might sometimes be higher than conventional solutions, the benefits are undeniable. Liquid waterproofing membranes, with their extended lifespan, can reduce maintenance and replacement costs over the building’s lifecycle. When coupled with reduced water bills, lower energy consumption for heating and cooling, as well as the environmental benefits of stormwater management and biodiversity; the lifecycle cost analysis favours these integrated sustainable solutions.

Challenges face UK architects and property designers but so are the opportunities. By embracing the power of liquid waterproofing membranes as the invisible backbone of sustainable design, especially on green roofs, we may be able to further unlock the benefits of - reduced flood risk, lower energy bills, improved air quality, enhanced biodiversity and significant water savings through innovative greywater reuse.

At Proteus Waterproofing, a one stop solution provider, we believe that every rooftop, every building, holds the potential to be a vital part of a sustainable future. Our Proteus Attenu8® full roof system, for example, uses BBA accredited waterproofing that states durability may last the lifetime of the building on which it is installed.