Pitched roof coverings 1: Wood shingle, slate & clay tile

Reclaimed slates and tiles
Timber shingles and shakes
Natural slate
Clay tiles

 

Key issues


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

 

Materials

Reclaimed slates and tiles


reclaimed 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.

Pro

Reusable

Pro

Down-cyclable

Pro

Negligible embodied energy if sourced locally

Pro

No toxic emissions from a manufacturing process

Pro

Diverts demolition waste from landfill

Con

Issues concerning quality assurance

Timber shingles and shakes


cedar shingles

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.

Pro

Reusable and recyclable

Pro

Very low embodied energy if sourced in the UK

Pro

Renewable resource but be sure to use FSC sources

Pro

Can be re-used though there are no facilities for recycling

Pro

Sequestered CO2

Pro

Production can make use of otherwise unusable logs and parts of logs

Pro

Light weight reduces roof loading

Con

Cedar shingles are usually treated with preservative

Con

High embodied energy associated with importation

Con

Maintenance issues

Con

Concerns over fire

Thermal conductivity

Western Red Cedar typically 0.11 W/mK

Density

Western Red Cedar typically 352 Kg/m3

Embodied energy

(Currently unavailable)

Life expectancy

30-50 years

 

Natural slate


natural slate

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.

Pro

Reusable and recyclable

Pro

Low embodied energy if sourced in the UK

Pro

Very durable

Con

High embodied energy if imported

Con

Accessible reserves in the UK are relatively low

Con

Slate quarrying can degrade landscapes

Con

High level of waste (around 90%) generated during production

Thermal conductivity

Typically 2.5 W/mK

Density

Typically 2691 Kg/m3

Embodied energy

0.1 - 1.0 MJ/kg (1)

Life expectancy


75 - 100 years - depending on quality

 

Clay tiles


clay tiles

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.

Pro

Reusable

Pro

Durable

Pro

Large reserves

Con

Clay extraction can degrade landscapes

Con

Very high embodied energy

Thermal conductivity

Typically 0.85 W/mK (3)

Density

Typically 1900 Kg/m3 (3)

Embodied energy

6.5 MJ/kg (1)

Life expectancy

50 - 70 years

 


References


1 Inventory of Carbon & Energy (ICE) - Version 1.6a - Hammond & Jones, Univ Bath
3 CIBSE Guide A 1999

Roof tile and slate products on GreenSpec

 

 


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