Roof Gardens

General

As the 'green' movement increasingly becomes a major factor in everyday life it has begun to influence the world of architecture, not only from the use of environmentally friendly building components, but increasingly in terms of internal and external landscaping and aesthetics, developing into the greening of roofs because of the extensive benefit they provide.

A modern trend is towards the construction of roof gardens and planter boxes. These provide green areas adding to the well-being of staff employed in the cities. Most often there are offices or living areas beneath.

Benefits

Environmental benefits:

• Improved insulation properties of structures.


• Aesthetically pleasing


• Provides natural habitat for bird life


• Control of air humidity and dust formation


• Rainwater retention


• Better utilisation of expensive land or normally redundant spaces

Technical benefits

Extra protection from:

• Temperature fluctuations


• Noise


• Ultraviolet rays


• Weather influences


• Mechanical damage

Green roof systems generally are divided into two categories:

• Intensive systems use deeper growth media - sometimes up to 1 meter and often are planted with trees and shrubs. In addition, intensive green roof systems can be extremely heavy - up to 1200kg/m2 when saturated - and would therefore, need to be applied on extremely heavy, strong roof decks such as structural cast-in-place concrete. The systems are expensive when compared with conventional low-slope roof assemblies.


• Extensive systems are much thinner than intensive systems and use plants with shallow root structures.

It is common that a combination of both intensive and extensive systems be used where thickness varies and XPS (extruded polystyrene) panels are incorporated to create an undulating effect.

Green roof systems require that careful attention be paid to the method by which drainage will be achieved. It is important that water be able to pass through the growth medium and between any joints of the extruded polystyrene panels until it reaches the sheet drainage layer that lies over the waterproofing membrane which drains to the outlets.
In some instances, it may be necessary to slow the drainage rate through the growth medium. The growth medium may consist of a combination of lightweight aggregate, nutrients, and organic materials.
If the drainage rate is too rapid, there is the danger that water will erode the growth medium. This may be achieved by incorporating several types of drainage fabrics in various areas of the roof.

Specification

 Outlets

The waterproofing is to be fully dressed into the drainage outlets to ensure a watertight seal. Outlets are to be positioned so that they are easily accessible both for the Waterproofing Contractor at the time of installation and maintenance purposes at some future date. Ensure that the level of the flange is kept below the screed level to prevent ponding around the outlet.

Flood Test

The integrity of the waterproofing system should be established by means of a flood-test of 48hrs – 72hrs duration, prior to handing over to the contractor. A certificate is to be obtained from the professional team recording the date and time-period of the test and that the waterproof treatment was handed over in a clean, proper and watertight condition.

IMPORTANT NOTE: Discuss plant choice with a landscaper, use plants with non-invasive root systems / root structures to avoid damage to waterproofing systems.

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