The challenge of clearly defining a sustainable roof is a near impossible task as the variants of the practice are plentiful.

Words that currently describe sustainable roofs create as much contradiction as clarity. Sustainable roofs may be described as “warm” and “cool”. They are not only “energy-efficient”, but also produce “clean energy”. Frequently, sustainable roofs are described by a particular colour that they exhibit:
• White to reflect the sun.
• Blue from captured storm water.
• Green from a living carpet of plants.
• Black from sheen of solar panels.

But behind these descriptions lies the fact that modern roofs serve many functions and impact the environment in many different ways:
• Energy-sustainable roofs can both save and produce energy. The potential energy savings available through the use of properly insulated roofing systems could exceed 700 trillion Btu each year.
• Water for hundreds of cities relying on antiquated combined sewer systems and the capture of rooftop storm water can play a significant role in reducing the amount of pollution that goes into our waterways. The use of this water for landscaping and other building-related needs can also reduce overall demand on municipal water sources.
• Air and climate in addition to saving energy during the air-conditioning season, as well as cool roof surfaces, help to mitigate heat-island effects in urban areas, reducing air pollution and global warming.
• Roofing waste accounts for over 40-million tons, or 5% of all solid waste generated annually in the United States. Improved use and reuse of roofing materials offer one of the best opportunities to reduce landfill waste throughout the world.

Far too often, building deterioration starts with a leaky roof that leads to marred interior surfaces, mould growth and structural damage. Developing new standards of roof system durability and roof asset management may significantly increase a building’s service life.

As public recognition of the complex role of rooftops has grown, limited descriptions of roof system sustainability based on a single characteristic are merging into a more comprehensive approach.

In terms of renewable energy, for example, new technologies might include solar energy systems and roof day-lighting, which in turn might require skills with solar energy modelling and electrical and lighting system design. New water-retaining roof technologies might require knowledge of climate modelling and landscape design, and examining energy-efficiency in light of new high-efficiency materials might require new knowledge of heat, air and moisture modelling.

With this in mind, effective systems integration emerges as perhaps the most critical challenge. What are the consequences of pursuing many different green strategies within a single building system? Will the use of certain technologies degrade or negate the effects of other technologies? What are the trade-offs and how can the overall sustainable contribution of the roofing system be optimised?

Because of the increasing complexity in sustainable roofing, more sophisticated design and decision tools are needed. In response, the Centre for Environmental Innovation in Roofing has developed a voluntary, consensus-based guideline for sustainable roofing systems called RoofPoint.

Materials used to maintain homes are becoming increasingly unique with the rise in popularity of sustainable home improvement. Recycled roofing materials are the most unusual yet practical components used to build or update eco-friendly homes. No matter the climate, there are sustainable, recycled roofing materials that can be installed to meet household needs.

High-quality roofing materials can be made from recycled plastic jugs and bottles in the place of wood or metal shingles. The plastic shingles are resistant to moisture, chemicals and harmful bacteria; and can be formed into any shape that a homeowner desires. Although it may seem an unusual choice, milk jug roof shingles reduce the need for new materials to be created while reducing plastic waste.

For homeowners seeking a roofing material that is sustainable and efficient, shingles made from recycled tyres are ideal. These lightweight shingles can withstand harsh winds and better insulate a home. Aesthetically, recycled tyre shingles may seem unusual, but they look like the typical shingles used to roof every other house on the block. Rustic-modern homeowners love wood as an unusual roofing material. Reclaimed wood shingles provide an earthy, grounded appearance to a home.

One of the biggest complaints about roofing materials is how heavy they are. Shingles made from recycled carpeting are extremely lightweight and carry the good looks of wood shingles as an additional benefit. Instead of sending scrap aluminium and steel to the junkyard, the creation of metal shingles should be considered. These shingles are very durable and will last much longer than the average shingle. Metal roofing materials can be recycled again and again, making them one of the most sustainable, unusual options.

The ability to endure and to keep on going is at the heart of sustainable design. When applied to buildings, sustainable design refers to product solutions that can conserve, recycle and even help to renew natural resources over time. Many products that accomplish this goal exist already, and new ones are being introduced every day.

For a design community faced with the rapid proliferation of new products and evolving performance standards, today’s challenge is maintaining the momentum for design solutions enriched by sustainable design concepts.

In efforts to promote sustainable design, the government and industry groups are rapidly evolving methods of applying uniform standards of measurement to certify performance.

Roof reflectivity can be achieved in a variety of ways. One of the most lasting methods is the application of a highly reflective topcoat or mineral surfacing. Although solutions are available for all types of roofing, their energy payback benefits are particularly significant when they are installed on single-storey, air-conditioned buildings with large roof surfaces and older buildings with insufficient insulation.

Metal roofing solutions are perhaps the fastest growing segment of the sustainable roofing market. Their sustainability derives from the fact that typically as much as 100% of their material components are recyclable. In other words — when the day comes that your client has to tear off the old roof and put up a new one — virtually the entire roof can be reused to create new metal products. In addition, many of today’s metal systems have long track-records for lasting performance. A copper roof that has protected a cathedral for over a century is sustainable — not only by virtue of its recyclability. It is sustainable because it keeps on going year after year.

Metal roofs also eliminate the fume and kettle concerns associated with some types of roofing, for easy and eco-friendly installation. And, with so many manufacturers introducing new products, finishes, colours, profiles and textures — today’s recyclable metal roofing is offering architects and designers a diversity of aesthetic features to support a wide spectrum of design concepts.

In the roofing industry, innovative manufacturers are also helping to reduce landfill problems by using recycled plastics or rubbers to create roofing that simulates the look and feel of natural slate. Manufacturing new products out of recycled materials is becoming increasingly common with other building components, such as carpeting.

Building-integrated photovoltaic (BIPV) materials integrate photovoltaic panels into a building to create power from the sun. The power is generated in the form of DC current that can be used directly or converted into AC current for future use. Many photovoltaic building solutions are available, offering architects and designers a wide variety of distinctive design solutions. Some solutions enable architects to make BIPV part of a building’s original design. Retrofit BIPV materials are also available.

Roof-mounted systems have the distinctive advantage of using the expansive and frequently under-utilised roof surface for placement. Whether integrated into the original building design or added later as an accessory, roof-mounted photovoltaic systems should be looked at as an integral part of a roofing solution.

BIPV solutions increase building sustainability in at least two ways. Firstly, by creating new power from a renewable energy source, thereby reducing peak energy loads and reducing energy costs. Secondly, they are likely to last 25 years or even longer. Recognising the community value of such solutions, many green pricing programmes are available to help offset the costs of investing in BIPV solutions.

Arguably the most exciting development in sustainable building design is green roofing. Although new green roofing products are being introduced more frequently than ever before, the best designs are integrated solutions that combine a:
• High-performance waterproofing layer.
• Root-resistant compounds.
• Drainage system that draws away excess moisture.
• Filter that prevents drain-system clogging.
• Specially formulated lightweight soil.
•  A surface layer of plant life.

Reflective surfaces can be artificially-altered surfaces that can deliver high solar reflectance (the ability to reflect the visible, infrared and ultraviolet wavelengths of the sun, reducing heat transfer to the surface) and high thermal emittance. The most well-known type of reflective surface is the cool roof. While it is true that cool roofs are mostly associated with white roofs, they come in a variety of colours and materials and are available for both commercial and residential buildings.

Cool roofs, in hotter climates, can offer both immediate and long-term benefits.

Cool roofs achieve cooling energy savings in hot summers, but can increase heating energy load during cold winters. Therefore the net energy saving of cool roofs varies, depending on climate.

If all urban, flat roofs in warm climates were whitened, the resulting 10% increase in global reflectivity would offset the warming effect of 24 giga-tons of greenhouse gas emissions, or equivalent to taking 300-million cars off the road for 20 years.

When sunlight strikes a dark rooftop, about 15% of it gets reflected back into the sky, but most of its energy is absorbed into the roof system in the form of heat. Cool roofs reflect significantly more sunlight and absorb less heat than traditional dark-coloured roofs.

The idea of painting our roofs and roads white to offset global warming is not new, but a recent study has calculated just how significantly white surfaces could impact greenhouse gas emissions.

If the 100 largest cities in the world replaced their dark roofs with white shingles and their asphalt-based roads with concrete or other light-coloured material, it could offset 44 metric giga-tons (billion tons) of greenhouse gases. That amounts to more greenhouse gas than the entire human population emits in one year.

Globally roofs account for about 25% of the surface of most cities. Even without cutting industrial pollution from its current levels, installing white roofs and pavements could offset more than ten years of emissions growth.

Full thanks and acknowledgement are given to James Hoff (Centre for Environmental Innovation in Roofing), Peter Wendt (writer and researcher), Brian Lambert (The Garland Company) and http://phys.org/news140875649.html for the information given to write this article.