Wallbarn adapted one of its products to create Protecto-drain20 for its green roof systems. It can hold water, prevent waterlogging, allow water to escape and help channel that water into where designers want it to go – all the elements needed for water control on green roofs.

Protecto-drain 20P was developed because of the need for a reservoir and drainage layer in green roof construction. Obviously, where soft landscaping is installed onto concrete roofs and podium decks, that concrete has to be waterproofed in order to protect the structure of the building, in exactly the same way as if it was exposed, or covered with hard landscaping.

Where this concrete deck is made watertight, without suitable outlets and drainage systems, water will simply collect in the bowl created, and if vegetation is planted in this environment, it will become waterlogged and die.

Therefore, a comprehensive drainage system for green roofs needs to be designed, and a means of getting water off the roof needs to be incorporated. Protecto-drain 20P allows for both of these.

Laid horizontally, the membrane is overlapped and covered with a loose laid geotextile filtration layer, and then the growing medium (the makeup of which will depend on the type of vegetation being grown in the green roof system).

The rainwater will work through the soil substrate and into the 20mm deep cups. These cups will hold approximately 5 litres of water per m2. The excess water will drain through the perforations between each cup and through the drainage channel out into the outlet.

The water held in the cups can then be drawn back up through the filter layer to nourish the vegetation above. This means that a constant level of water can be held in the reservoir cups, but rainwater is efficiently removed effectively and quickly from the roof, which will not become overloaded (never underestimate the weight of standing water). Because of the egg-box shaped of the membrane, a constant air gap beneath the HDPE is maintained, allowing the excess water to pass easily without clogging.

It is important to remember, however, that these materials do not alone provide a drought-resistant system. Regular watering and maintenance is required for all roof gardens and green roofs

Please see further details of Wallbarn green roof systems here.

Wallbarn Protecto-drain is lightweight and easy to transport and install, making it ideal for rooftop applications. It is the perfect product for either large-scale roofs or small domestic projects. Large amounts of the membrane can be installed in a day, as operatives can simply roll it out across the deck and overlap the edges quickly and easily. By installing the soil substrate immediately, the membrane is properly ballasted.

Although very tough, it is also very flexible, meaning it can be shaped around details and corners effectively without interrupting the drainage function. The membrane can be cut around edges easily without affecting the system in any way.

Protecto-drain holds a fair amount of water within its profile and helps to slow down the run-off of water. Therefore the moisture level within the soil substrate is maintained, a more efficient way to nourish plants.

Protecto-drain 20P is suitable for EXTENSIVE green roofs. This includes sedum roofs, wildflower and biodiverse roofs, grasses and dwarf plants, where soil substrates are up to a depth of 200mm.

For INTENSIVE green roofs, installers will need to use Wallbarn Protecto-drain 60P as the drainage membrane.

Please see our green roof pages here Green Roof Systems for more details.

Technical Data
Technical features Technical data Test Method
Material High-density polyethylene (HDPE)  
Roll width 2 metres calibrated measuring tape
Roll length 20 metres calibrated measuring tape
Roll weight 550 gsm (±10%) calibrated thickness-measuring tape
Rolls per pallet 5  
Compression strength 180 kN per m2 MDV
Height of cups 20mm MDV
Air volume between the cups 14 litres per m2 MDV
Water drainage capacity 10 litres per m2 MDV
Temperature tolerance – 30°C to + 80°C MDV
Reaction to fire B2 (B1 available by special request) DIN 4102
Physical characteristics Rot-proof, resistant to fungus and bacteria. Will, not leach chemicals. Not harmful to drinking water. No health hazards under normal use

Used as mechanical protection against soil and root movement along foundation walls. It can be installed with a 20cm overlap and fixed with nails and sealing buttons 5 cm from the top edges of the roll and 20cm from each roll. Edging profile is installed to prevent soil ingress into the cavity. The maximum build-up is 8 metres high.

Laid horizontally and fixed using sealing tape in the overlapping areas the sheets protect concrete flooring form rising damp and keep reinforcement mesh in place firmly during the concrete works.

Storage and handling

Protect against prolonged exposure to direct sunlight and temperatures over 25 °C.


When used in the correct manner and application, the material will be rot proof for 20 years. Wallbarn application rules and proper site storage, handling and installation practices must be carried out as a prerequisite for any possible future warranty claims.

Health and safety

No known dangerous substances

This datasheet represents the current knowledge of the product but may be revised by Wallbarn in the future. It is the duty of the customer and installer to be clear that this product is suitable for the purposes it is used for.

This technical datasheet may be revised or changed at any time without prior notice. It is the duty of the customer and installer to be sure they possess the latest version of the datasheet.

To download our current brochure (in Adobe Acrobat PDF format) please click here.

Wallbarn Protecto-drain is high-density polyethylene (HDPE) cupped drainage sheeting which acts as a protection and drainage layer for waterproofed surfaces.