When designing a green roof, it is important to consider the environment, intent, and building requirements. The information below can help you get started, but it is not intended to be a comprehensive design guide. It is strongly advised to hire a professional design-build firm consultant to guide you through the design process, assist with procuring funding and permits, and safely install and maintain your green roof. Assess the following elements to help determine the roof’s design.
Climate and microclimate (roof height, sun and wind exposure, and average precipitation)
Roof slope, the age of the waterproofing membrane, and building HVAC systems
Structural capacity, including dead load and live load
Accessibility for ongoing maintenance and egress
Rainwater harvesting and drain locations
A water source for irrigation and power source for installation or lighting, if needed
City sustainability requirements, building codes, and insurance requirements
Growing zones: NYC is growing zone 7 but green roofs may be closer to a zone 5 depending on wind and exposure
Types of Green Roofs
Shallow growing medium (soil) between 2 and 6 inches
Less structural support
Limited plant diversity with less intricate root systems
Less investment and little maintenance once established
Requires minimal maintenance after the first year
For roofs without occupancy or capacity for gathering
Extensive Green Roof
Intensive Green Roof
6+ inches or deeper growing medium (soil)
Greater weight bearing capacity to support deeper growing medium and heavier plants
Can support a larger variety of plants and trees
Can support raised beds
Higher initial investment and more intensive maintenance
May require an irrigation system
May be accessible for residents to socialize, with appropriate access and Certificate of Occupancy
Typical Green Roof Layers
The type of vegetation will vary depending on a roof's other qualities and microclimate. Sedum varieties are the plants used most on green roofs because they require little water and maintenance. Deeper substrates allow for a wider variety of plants to be planted.
Growing Medium (Soil)
Soil for green roofs must be lightweight, porous, and contain nutrients. Consider adding shale, perlite, ash, volcanic rock or other porous materials for optimal water retention and compost, organic fertilizers, and slow-release amendments, and/or mulch appropriately and as needed.
The drainage layer guides water runoff during and after a rainstorm towards a drain or gutter. It is designed to ensure that stormwater may be used by plants for longer periods of time. An irrigation system for supplemental water may also be needed, depending on the vegetation used.
Insulation may be inserted above or below the waterproofing membrane to provide additional cooling, noise absorption, and further lower energy costs.
Membrane Protection & Root Barrier
The flexible material is placed on top of the roofing membrane to protect against roots perforating the roof and causing leaks.
The waterproofing membrane protects the building against water leaks and may extend the longevity of the roofing membrane.
This refers to the underlying structure of your building and how much load (weight) it can hold. The weight of the entire green roof layer assembly, including plants and the water required to saturate the vegetation, should be considered when assessing what your building's structure can hold. Green Roofs with public access and recreational spaces have additional weight-bearing requirements.
Plants on Green Roofs in NYC
Rooftops can be challenging places for plants to thrive. Direct sunlight, extreme temperatures, wind, and precipitation affect which plants survive on a green roof, so plants should be selected to withstand harsh environments.
Extensive green roofs are comprised of sedum or groundcover. Deeper semi-intensive and intensive green roof systems can support native plants, wild grasses, shrubs, and even trees, though they require more maintenance than simpler extensive green roofs.
Sedums & Groundcover
Flowers & Grasses
Produce & Herbs
Cost-benefit Considerations for Green Roofs
Green Spec UK
Vegetal ID Extensive Green Roof Design
NYC Parks Innovative Green Roof Design
Green Roof Handbook