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The roof is a very important contributor to the environmentally friendliness of a building. Heat rises through a building and without a properly constructed and insulated roof, as much as 15% of a building's heat can go straight out.
The most common way to prevent heat from escaping is to insulate the roof. This involves putting either mineral or natural wool in rolls or boards. Natural wool is more sustainable but mineral wool can contain recycled materials.
Using 270 mm of insulation in a roof will allow heating bills to come down by as much as £110 and save around 1 tonne of CO2 per year. The DIY cost to insulate an average roof is around 250GBP, paying back within 3 years.
Flat-topped structures are ideal for green roofs. These roofs have a layer of soil on top, which can support vegetation and even wildlife in the form of insects, birds etc. Developed in Germany during the 1960s it is estimated that green roofs can be found on 10% of the nation's buildings.
The use of green roofs increases a building's thermal mass both taking in more heat from external sources (sunlight) and preventing heat from within the building from escaping. Green roofs can also impact a wider area then just the building they are fitted to. Using green roofs reduces the water run off during rain, Allows local wildlife and vegetation to flourish in an urban environment and reducing the CO2 of the atmosphere with the vegetation converting it back to oxygen.
A study by Environment Canada found that green roofs reduced the need for heating by 26% in the winter and cooling by the same amount in the summer.
A green roof will weigh significantly more then tiling and so careful inspection of the existing roof will be needed to make sure they can take the weight. When planning a new build, a green roof considered from the start will be easy to install and low maintenance throughout its life.
Where a conventional design is in use (such as an existing build) there are a few options available to improve the green credentials of a roof.
Many roofs in the UK use grey slate tiles, these come from non renewable or sustainable sources often from mines located in Cornwall or Wales and are also prone to cracking and shattering in extreme weather conditions allowing water in and heat out.
AthyEcoSlate is manufactured from recycled plastic saving on the need to use new material. The tiles are generally far lighter then the equivalent slate counterpart allowing lighter roof structures to be used and, unlike slate tiles, they do not crack and are virtually unbreakable. They are easier to install often able to be screwed down instead of using heat and water-intensive lime mortar. Due to their plastic construction many suppliers will also buy back unused tiles and offcuts at a similar rate to the one they were sold at, reducing site waste and allowing the tiles to be recycled.
Instead of using non-sustainable mined slate tiles, a visually similar and far better insulation cover can be gained using composite roof tiles, which are actually thick slabs made of crushed recycled materials. These slot together easily and are also cheap and far more environmentally friendly.
Scantile slating is a method of roofing found mostly in the far South West UK. It involves laying different size slates on a bed of lime mortar in even and diminishing courses. Hand made hardwood pegs are used to secure the slates to 'hand cleaved' riven lathes. The underside of the slate is then finished with a lime plaster. The slate arrives on site in large blocks and is cut on site into the sizes required. Whilst this method is traditional, durable, and can take advantage of local slate, it requires a lot of skill and uses energy intensive lime mortar.
Other materials can be used to create roofing tiles/shingles. Wood used to be a popular material and has the advantage of being able to be sourced from renewable forests, it does however lack the flame protection most people now require.
Building-integrated photovoltaics (BIPV) are roof tiles which have a photovoltaic membrane allowing them to generate electricity whilst providing the weather protection of a normal roof tile without looking out of place compared to a solar panel.
Cement-Fibreglass shingling is very strong, durable, flame resistant and can be made to feature a high percentage of recycled material. It also helps increase a building's thermal mass compared to lighter plastic/rubber tiles.
Thatch Thatch roofs made from reeds or wheat were a traditional method of roofing found in the UK. However the roofs carry high maintenance regimes often requiring a rebuild after a few years as well as carrying a high fire risk. This has led to them falling out of favour and in some places they are banned on new builds and getting insurance on existing builds is hard and expensive.
Three main thatching materials are Combed Wheat Reed, Long Straw and Norfolk Reed. These use different techniques and are used in different parts of the country. Skilled local thatchers are best employed.
For lots more thatch information see www.thatch.org
Artificial thatch in the form of matting to be rolled onto the roof has been created out of plastic, which can be from recycled sources, and provides better insulation than its natural counterpart.
Heat protection and retention
Roof design is also important to maintaining heat in a structure. Where passive solar design is to be used it may be worth considering the sun's height in the different seasons and adjusting the roof accordingly.
A practical example of this is to build an overhang into the roof so that when the higher summer sun beats down it is partially blocked by the roof to prevent overheating. In the winter when the sun is lower in the sky it will have a clear path warming the room to its full potential.
Roof design can play a major part in green building. The strength of a roof determines what technologies can be added to it (i.e. solar panels, turbines, green roof etc.) and the materials used can all play a part in keeping carbon emissions down by optimising heat retention in the building.