Design and Development of a Roof Garden
- Design Parameters -
(page 6/10)

minimum of 16” of soil is required. For small trees and large shrubs 24” is needed and shade trees require a minimum of 30” of planting medium.

Wind
Trees and vertical structures (such as fences, walls, gazebos, trellises and light standards) and other similar elements must be designed or selected to resist wind damage due to overturning or breaking. Plants are also subject to flagging (lopsided growth) due to strong persistent winds, which are typical in a roof garden application. Further, even normal wind flow can cause excessive drying of plant materials and soils and high evaporation of water used in water features. Special guying and support of trees is required to offset the effects on trees of persistent winds. Automatic water fills are required on water features to compensate for evaporation and to protect pumping equipment. And irrigation is required to replenish the soil moisture.

Wind direction should also be considered in the design of the barrier system, designing such systems to mitigate the effects of wind on the garden’s visitors.

Sun and Shade
Heat and glare can make a roof garden quite uncomfortable. Except for the confirmed sun worshiper, few people prefer to be in the sun for more than a few minutes on a hot day. Shade relief, usually found under trees, may be at a premium. Trees should be located where they cast the greatest shadow. Artificial shade should be provided in areas where trees cannot adequately shade the area. Providing adequate shade maybe the single most important design consideration in relation to the use of the roof garden. If adequate shade is not provided, the garden will receive little or very limited use.

Glare is also a significant problem even in areas where heat is not an issue. Avoid using light colored paving or paving that has a high reflection value. Glare is not relieved by immediate shade in the area of the user and a rooftop garden is seldom planted so closely with trees as to eliminate the problem. Glare reduction can, however, be achieved by using lawns and groundcovers and light absorbing paving materials.

KEY POINTS: Climatic Conditions
The effects of wind, heat, cold and precipitation are amplified on roof gardens.

• Provide adequate soil mass to support the desired plantings.
• Make appropriate provisions to replenish soil moisture and water in features to combat the effects of evaporation.
• Use windscreens to mitigate the effects of wind on the users.
• Plant trees in areas that will cast the maximum amount of shade.
• Avoid using paving that increases the amount of glare.