Green Roof

Introduction

According to a South African case study, "Small, local solutions can crack water crises"

Before you get started on any project, always be careful to check your local legal codes and policies. Some types of water harvesting are forbidden in certain places for a variety of reasons. 

North America

You may also be interested in reading about:

Learn about which activities use the most water, to develope a plan on curring your own water footprint. In many cases consuming less will have a greater impact than harvesting water, though water collection may be your first step in your water conservation journey.

Basics of Green Roofs 

This takes every drop of water that lands on a rooftop, directing it to a gutter which can collect it in rain barrels or cisterns for later use. Any overflow can be directed towards water harvesting landscape features such as water gardens, however these features should be at least 3.33 meters (10ft) from any structures and their foundations.

Safety

How safe is roof-water to drink?

Life Expectancy: 40-50 years.

Pro: Captures precipitation that might have otherwise contributed to run off and flooding. Increases biodiversity. Reduces energy costs associated with heating and cooling buildings. Extends roof life. Reduces emissions not just by reducing energy use, but the plants can sequester greenhouse gases.

Con: Relies on precipitation, meaning it may be unreliable in drier climates. Plants need a small amount of care, including occasional trimming, removal/replacement of dead plants, and removal of invasives. Water collected by these roofs may not be appropriate for drinking or other domestic activities.

Solution: People who receive seasonal rain should build ample storage space to help capture as much rain as possible, ensuring more water will be saved for later in the year. They may also want to consider other options such as a well with recharging infrastructure, a grey water system, etc. Special filtration will be needed if people want to drink water collected from green roofs.

Fuel Types: Water Cycle + Gravity

Life Expectancy: 10-25 years, but some components made from certain materials can last 50-100 years. Green Roofs are expected to survive for 40-50 years.

Pro: Captures precipitation that might have otherwise contributed to run off and flooding.

Con: Relies on precipitation, meaning it may be unreliable in drier climates.

Solution: People who receive seasonal rain should build ample storage space to help capture as much rain as possible, ensuring more water will be saved for later in the year. They may also want to consider other options such as a well with recharging infrastructure, a grey water system, etc.

Fuel Types: Water Cycle + Gravity

History of Green Roofs 

Historically, sod roofs were lines with birch bark for it's water repellent properties, before sod was applied on top to provide insulation. Green roofs use plants to absorb rain, instead of adding to run off. The plants absorb carbon, provide additional insulation for us, but also provide habitat and food for wildlife.

"Green roofs are being increasingly used in urban areas where space constraints limit the use of other stormwater management practices." - https://www.epa.gov/soakuptherain/soak-rain-green-roofs 

Green roofs need to be installed on roofs pitched at no more than 30°. 

These can serve a number of purposes from increasing pollinator or veggie space, to reducing pollution and run off into our water ways. They can even help buildings stay slighter warmer in winter but are better at keeping things cooler in hotter months. According to this source "it is quite common to harvest water from green roofs in Germany and Switzerland." Thought some designs function as zero discharge sites, where "All water is reused within the development, either to irrigate intensive green roofs and landscape at ground level or is used to flush toilets throughout the development." 

Green roofs can absorb up to 70% of the water that lands on them. So if you want to harvest drinkable or reusable water, then these may not be the best choice. However they will still preform the other functions just fine, and are a great solution to helping reduce flooding or run off.

According to this article "There are three basic types of green roof: intensive (thick), extensive (thin) and semi-extensive (somewhere in between).

Intensive systems consist of a thick layer of soil (50-200mm+) in which a variety of grasses, herbs, flowers and shrubs can grow. These need to be accessible gardens (for maintenance) and can even be used as a recreation space. They provide a valuable habitat for wildlife but place significant weight on the building and need substantial roof support. They offer good insulation and better water absorption than the thin types, but need a lot of care.

Extensive green roofs are generally made up of a shallow layer (20-100mm) of substrate planted with low-growing, stress-tolerant grasses, mosses and sedum. These lightweight systems require little maintenance. The insulation quality is relatively low and extensive systems always incorporate conventional insulation.

Semi-extensive Systems have slightly greater depth than extensive systems (100-200mm) but constructed on the same principles to allow for a greater diversity of plants. It is also relatively low-maintenance."

Are Single Ply Flat Roofing Membranes Suitable for Use in Green Roof Systems?

BAUDER: Green Roof Systems Brochure (PDF) this shows not only a wide variety of green roof designs, but breaks down different types that are available, the benefits and differences between them, as well as diagrams of different examples of system configuration. For example different mat layers with substrates vs pebbles or paving. There are also examples of the different fixtures such as sky lights, and some of the equipment used to install industrial-sized rolls of grass.

Build a Living Roof / Green Roof Step by step instructions for converting a small, flat, existing roof into a green roof, complete with photos.

Green Rood as a Retrofit Option Case studies of large buildings include the methods they used and why those features were included.

Green Roof Gardens and Green Living Roofs "Green roofs have been constructed for thousands of years, the most famous early example being the Hanging Gardens of Babylon.

They have also been used in traditional buildings such as the sod roofs of rural Scandinavia. Experimentation in the earlier part of the 20th Century found that green roofs required special waterproofing, since roots were found to grow into what were typically tar roofs." Article continues explaining modernization in green roofs, and that some roofs don't even use soil in an effort to reduce weight, that they often don't need irrigation, and provides links, photos and a checklist explaining benefits and designs of these roofs.

Green Roofs: The Ultimate Guide this article was quoted above but also includes cost (UK), planting suggestions, suggestions for drainage layers, photos, and other useful information.

How to Create a Simple Low-Cost Green Shed Roof This talks about weight load and which membranes can be used to prevent leaks.

How To Grow Your Own Green Roof Plants "You might be unwilling to spend a lot on expensive green roof plants for your shed roof if this is your first foray into this field. This article shows you how to source plants for your new roof in a low-cost way."

Minnesota Stormwater Manual: Green Roofs Combined This is a massive amount of info with diagrams, photos, comparisons of different roofing types and greenroofs vs natural prairie bluffs, naturally seeded vs gardens planted with plus, as well as progression photos showing how plugs and seeded roofs become lush over time. Planting lists, terminology, drainage info, case studies, performance assessments, etc.

New Green Roof Lab “As things stand, there are a lot of different green roof systems—each with something different to offer. Some can hold back large amounts of rain, while others promote plant and animal life. The problem is that they’re all grouped together. It’s like comparing pears and bananas, which doesn’t work,” a technical sales consultant commented of the reason this lab has been set up at DTU Ballerup Campus, Denmark. 

Rainwater Harvesting on Greenroofs? This page has diagrams and a chart, explaining how to harvest drinkable water from green roofs without contamination. The include laws about roofing materials for collecting drinkable water, as well as a caution to only use the collected water for drinking in extreme cases, that it would be better used for irrigation.

In the materials I have found on the topic, it is highly suggested that rooftop water be considered "wild" and should therefor be boiled before drinking.

Complimentary Options

Blue Roofs 

Hydropanels

These can be set on the ground or on rooftops.

Additional Equipment

Rain Barrels/Butts & Cisterns 

Life Expectancy: 20 years.

Pro: Safely stores rain or grey water for later use.

Con: An turn into a breeding ground for mosquitoes, or be contaminated with dead animals that can fall/get trapped inside. I've found dead frogs who might have hatched but not been able to get out. Dead leaves can build up, leaching tannins into the water.

Solution: Install fixtures that will help keep wildlife and leaves out of the system. Make sure to clean these to prevent plugging and backups. Empty and clean out the container periodically.

Fuel Types: Water Cycle + Gravity

Alternative At-Home Water Harvesting Options

Water Recycling 

Grey Water 

Simple Greywater Systems For Your Home "A greywater system is used to take water that has already been used from places like your laundry, shower and sink and divert it to use in another purpose like watering gardens or landscaping instead of flushing it down into the sewer. Greywater is different from blackwater (aka sewage) because while it may have some residuals like dirt, hair, grease, etc from it’s first use, they aren’t toxic to the environment and the water can be reused in some applications." When using a grey water system for irrigation, it is important to be very careful in choosing "bath soaps, used homemade shampoos and biodegradable dish soap so as not to damage the soil, plants or watershed." Link talks about legal issues, installation costs, and design elements such as filters.

Toilet to Tap Water Recycling

Toilets can use grey water, function without water, or be a source of water depending on the type you choose, and the infrastructure around it. 

Tools & Resources

Landscaping Know-How

This may give ideas for how to capture and redirect water on the land, which can integrate well with rooftop water harvesting.

Organizations

International

Africa

Asia

India

Europe

UK

North America

Mexico

USA

Oceana

South America

Maps

North America

USA

Grants & Funding

Oceana

Australia

Western Australia

Further Reading