A roof garden is any garden on the roof of a building or a house. Besides the decorative benefit, roof gardens provide for temperature control, architectural enhancements and recreational opportunities.
The main issue is that the time and expense associated with future repairs of membranes to be put on roof gardens prohibit the use of an “economical” 10-15year membrane system. The membrane must be durable enough to resist mechanical damage from gardening tools, the penetration of plant roots (very vital) and last without repair or replacement for the life of the building. It is essential that the architect considers membrane systems that have worked within this configuration in previously successful applications. Membrane systems that are new to the roofing industry do not have the performance record required for these roof garden applications.
Roof membrane materials are constantly exposed to weathering elements – sun, wind, rain, etc. For the most part, water buildup is removed from these areas within 48 to 72 hours, with prolonged exposure concentrated to cold months. Roof system materials generally have a service life of 10 to 20 years prior to the institution of remedial actions. Their remedial construction – whether it is removal or replacement – can be accomplished utilizing routine construction methods with (in most cases) minor inconveniences in the building due to ease of accessibility to the roof.
Below-grade waterproofing products are not exposed to weathering elements. However, they are exposed to constant water buildup, which in garden construction could exist for two to three continual months due to saturated soil. Below-grade waterproofing systems are also continually exposed to ground and soil chemicals. Properly applied waterproofing systems can have a service life that matches the life of the building. This is an important characteristic, because unlike roofing materials, the waterproofing materials are inaccessible and the expenses associated with repairs and replacements are substantial.
There are four essential components to the roof garden component. They are:
- The Waterproofing layer.
- Geotextile Filter Fabric.
- The planting medium.
- Top dressing/soil.
Positive drainage is critical requirement of rooftop garden design. Proper drainage is critical within the whole total system
EPDM Membrane as the Waterproofing medium
Rooftop gardens play an integral role in slowing down water runoff from the roof. It has been established that the soil in the garden can retain 15 to 20 percent of rainfall for a two- to three-month period. The water retained in the soil also helps the plants thrive.
Whether you want a true garden where you’re going to be able to plant, or a decked garden where you’re going to plant yourself at the end of a long day, think of your rooftop garden as a series of layers. The bottom layer is waterproofing, and is therefore the most important. EPDM is waterproof and durable, being highly resistant to ultraviolet light. It’s also flexible, able to elongate by as much as 310% to accommodate any movement in the structure, as well as being able to withstand temperatures as low as -54C and as high as 154C. EPDM rubber is also resistant to a wide-range of other substances, like mild acids and alkalis, oils, alcohols, and more.
Note that EPDM rubber needs to be covered by a layer e.g. a geotextile fleece. This will protect it from damage, and will help retain moisture for the garden. Above that you need layers for drainage and soil retention before you get to the green layer and planting.
If you’re going for a decked rooftop garden instead, then EPDM rubber’s waterproofing will again prove vital, as will its strength.( As before, consult a professional to make sure that your roof will be able to bear the additional weight).
Due to these conditions it is often misconceived that roof drainage is not required on rooftop garden systems. This theory is not only incorrect – it is potentially dangerous. The water needs to be removed from the system to comply with the structural constraints of the building. This additional dead load weight, coupled with the excessive live load weight, could result in substantial structural damage.
For new structures, the roof drain pattern must meet the design requirements specified. Positive roof slopes to the drains can enhance proper drainage.
The drainage medium is applied above the waterproofing system and consists of a rot-proof material that allows the water to flow through to the substrate drains. This is a critical component, which must be compatible with the filter fabric and the planting medium. Successful roof drainage systems reduce the blockage of water to the substrate drains and assist in the elimination of excess water on the system.
New drainage systems have been introduced to the market in recent years with more products being introduced as the market segment of these systems expands. As with all new products, it is imperative that the designer conducts a background search of these products prior to design.
Geotextile Filter Fabrics
Geotextiles filter fabrics are installed to prevent the loss of soil, mulch or plant debris while allowing for the flow of moisture to the drains and keeping the drains unclogged. The geotextile filter fabric also keeps the planting medium in place. A durable geotextile filter fabric can serve as a root barrier protecting the roof membrane.
Planting Medium and Top Dressing
There are various forms of soil composition that are suited for rooftop gardens. The success of the plantings often depends on the types and depths of the planting medium. A landscape architect or consultant should be contacted for advice with these design requirements.
FOR TECHNICAL HELP:
Phone: + 254-02-2358486, +254-20-422949/50
Email: [email protected]