• Embodied energy - there's a wide scale of embodied energy from wood shingles at the low end of the range to aluminium at the high. The main energy components are those derived from manufacture and transport. As with other materials, sourcing a product in the UK (and close to site if possible) can dramatically reduce its embodied energy.
• Material efficiency - Selecting a material can be made more complicated once its efficiency is considered. For example in some circumstances it can be argued that a strong, lightweight material used over a large span can have a lower environmental impact than a heavier, more sustainable material once the degree of structural support is introduced into the equation.
• Durability - The longer lasting roofing material has a lower environmental impact
Reclaimed slates and tiles
Assuming that there is a quality-assured source of sufficient quantity available for the job, there are few excuses not to use reclaimed slates and tiles.
Negligible embodied energy if sourced locally
No toxic emissions from a manufacturing process
Diverts demolition waste from landfill
Issues concerning quality assurance
Timber shingles and shakes
As a sustainable roofing material, the timber shingle can only be matched in its low environmental impact by thatch. If sourced in the UK it has the lowest embodied energy of all roof coverings. Western Red Cedar is commonly imported from the west coast of Canada where transport adds considerably to the embodied energy figure. Care should also be taken in specifying FSC sources as a number of imported timbers are unsustainably harvested.
Shingles have relatively smooth faces and backs, while shakes have a highly textured, natural grain face and either a sawn or split back.
Cedar shingles used in the UK are usually treated with preservative to meet with the higher risk of decay in this country. A small number of projects have been completed using larch and oak, but feedback is as yet inconclusive.
Reusable and recyclable
Very low embodied energy if sourced in the UK
Renewable resource but be sure to use FSC sources
Can be re-used though there are no facilities for recycling
Production can make use of otherwise unusable logs and parts of logs
Light weight reduces roof loading
Cedar shingles are usually treated with preservative
High embodied energy associated with importation
Concerns over fire
Western Red Cedar typically 0.11 W/mK
Western Red Cedar typically 352 Kg/m3
If sourced in the UK, natural slate has a very low embodied energy. Imported slate often comes with quality issues along with added embodied energy from transportation. Slate is very durable and can be reused with relative ease.
Reusable and recyclable
Low embodied energy if sourced in the UK
High embodied energy if imported
Accessible reserves in the UK are relatively low
Slate quarrying can degrade landscapes
High level of waste (around 90%) generated during production
Typically 2.5 W/mK
Typically 2691 Kg/m3
0.1 - 1.0 MJ/kg (1)
75 - 100 years - depending on quality
Clay roof tiles are made from similar clays to bricks and come in either plain or profiled formats. Like bricks, tiles can be hand-made or machine-made. Machine-made tiles come with either a sand or smooth-faced finish whilst hand made tiles will be sand-faced from the material used to line the mould.
Like bricks, clay tiles are a feature of this country's vernacular landscape with both tiles and bricks often owing their origins to often long defunct local clay pits. Tiles also share with bricks a similar method of production which can involve landscape-degrading clay extraction and high levels of energy used in the firing of clay.
Manufacturers claim to be making progress in reducing their environmental impact through investment in modern plant to improve firing efficiency and reduce flue gas emissions.
Clay extraction can degrade landscapes
Very high embodied energy
Typically 0.85 W/mK (3)
Typically 1900 Kg/m3(3)
6.5 MJ/kg (1)
50 - 70 years
1 Inventory of Carbon & Energy (ICE) - Version 1.6a - Hammond & Jones, Univ Bath
3 CIBSE Guide A 1999
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