Waterproofing:
The waterproofing system beneath any green roof MUST be root resistant in the long term preferably to the German FLL standards. If the waterproofing is not root resistant then the green roof system must include a root barrier. The installation of the waterproofing and its detailing to perimeters, outlets, protrusions through the roof etc., MUST take into account the depth of the green roof build up. The waterproofing should always be 150mm above soil level at internal upstands and protrusions, and at least 50mm at external perimeters. The waterproofing system must be leak tested and certified as such IMMEDIATELY before the installation of the green roof.

Green Roof System:
No matter what species of plants are specified, for them to flourish the green roof system MUST provide them with:
◦Moisture
◦Drainage
◦Aeration to the plants root systems
◦Nutrients
To achieve this, a successful system must basically replicate nature but within a very compressed build up. The build up should ideally consist of:
◦Moisture retention/protection layer
◦Drainage layer
◦Filter layer
◦Manufactured/Recycled Growing medium
◦Appropriate components i.e. outlet inspection chambers etc. The type, size, and design of each layer will depend on the proposed vegetation; as will the need or otherwise for irrigation
◦In the absence of a British Standard, green roof systems should conform to the German FLL standards. This standard is generally recognised as the benchmark for green roof quality, certainly within Europe

John Ruskin said; “It’s unwise to pay too much, but it’s worse to pay too little. When you pay too much, you lose a little money — that is all. When you pay too little, you sometimes lose everything, because the thing you bought was incapable of doing the thing it was bought to do.”