Rainwater goods

Cast Iron & Steel
Glass Reinforced Polyester (GRP)


Selecting the rainwater goods material with the least environmental impact is fraught with 'ifs and buts':

• In light of production processes which use large amounts of energy, metals look a doubtful prospect. But on closer examination of output, it is possible to see an industry that makes increasingly best use of recycled content - so possibly mitigating the impact of producing virgin (or 'primary') iron, steel, aluminium and copper. In considering the specification of metal rainwater goods, we would urge designers to examine the product manufacturer's material sourcing policy: 'Where does the metal come from? ' 'What kind of energy is used in the production process?' and 'How much of the product consists of recycled material?'

• Of the plastics alternatives, both GRP and PVC, are materials that depend on petrochemicals. GRP is probably the better choice because of its lesser dependence on oil; whilst PVC is a hard call for the many who believe that its production and disposal processes are potentially dangerous. Because both sides of the PVC debate are vociferous and prone to mis-lead, we would recommend designers review the evidence with a critical eye.

• Our own favourite is wood, the oldest form of guttering - common use of which, sadly, is fading from memory. Sourcing timber guttering has become notoriously difficult, but we would encourage specifiers to make the extra effort where possible and help in restouring this once traditional material to the designer's palette of materials. (A short list of suppliers / installers is provided at the foot of the page)


Embodied energy

• Of all the common metals used in construction, aluminium is noted for its very high level of embodied energy resulting from the smelting of its raw material, bauxite.
• There is an exception: though most bauxite is smelted using electricity generated by fossil fuels, a significant quantity of aluminium is produced using hydro-electricity. This is particularly true of aluminium produced in Norway, where nearly all electricity is derived from hydro.
• Though the use of hydro-electricity significantly reduces the amount of embodied energy, it does not eliminate it – this is because virgin aluminium uses coke as a raw material in the production of carbon anodes.
• The specifier should check with the manufacturer the nature of the energy used in production.

• Cast virgin: 222.5 MJ/kg (1)
• Cast recycled: 24.5 MJ/kg (1)

Recycled content

• Aluminium products contain, on average, 33% recycled aluminium. Quantities vary however and some products might be distinguished by their higher-than-average recycled content. When specifying, it is safe to assume that the product will contain an element of recycled aluminium - but the percentage should be checked with the manufacturer.

Design Life

40 - 60 years (2)

Pro Recyclable
Pro Durable
Pro Material efficiency realised through thin sections
Pro Lightweight
Pro Products can include high levels of recycled material
Con High embodied energy (but see above)
Con Painted and powder-coated aluminium is difficult to recycle

• See also 'Aluminium production & environmental impact'


Cast iron & steel


• Coke production, an essential element of most iron and steel production, is a major source of VOCs and carbon monoxide emissions. Waste water from coke making has high contaminant levels, requiring extensive removal and treatment before disposal. Though emissions from iron and steel production have been much reduced through controls and technology, the environmental impact is still significant.
• Blast furnace iron making generates large quantities of sulphur and nitrogen oxides and carbon monoxide.
• Compared with the West, the environmental impact of steel and iron produced in China is relatively un-regulated. Though the situation is improving, the world’s largest producer remains a subject of concern.

• 95% of the cast iron manufactured is used in the production of steel. Steel is formed by treating molten iron with intense heat and alloying with carbon. The extra process increases embodied energy and releases further CO2 as well as dust, cadmium and fluorine compounds

Recycled content

• Much of the environmental impact of iron and steel production can be mitigated by the use of recycled material.
• Typically, cast iron rainwater goods can include around 70 – 75% recycled content.

• Worldwide, around 42% of the annual steel production is made of scrap. Using recycled steel uses approximately 30% of the energy associated with producing virgin steel. Steel rainwater goods can be expected to have a recycled content of about 70%.

Embodied energy

• Cast iron: 25 MJ/kg (including and unknown % of recycled content) (1)
• Steel pipe: 34.4 MJ/kg
• Stainless steel: 56.7 MJ/kg
• Galvanised steel: 39.0 7 MJ/kg
(figures assume 42.7% recycled content) (1)

Design Life

60 + years (2)

Pro Recyclable
Pro Durable
Pro Products can include high levels of recycled material
Pro Iron is particularly resistant to damage
Con Extraction can lead to considerable landscape degradation
Con High levels of waste are associated with iron & steel production
Con High embodied energy involved in production
Con High embodied energy associated with import transportation
Con Iron needs regular painting
Con Steel needs painting, galvanising or other coatings
Con High levels of pollution including dioxins

• See also 'Steel production & environmental impact'


• Copper is a popular choice for rainwater goods in Europe. Its main attraction is its resistance to corrosion. Copper naturally oxidizes to a verdigris patina over a period of time (though this process can be artificially stimulated).
• Copper is a very limited resource. Optimists expect 60 years but some think it more like 25 years before supplies are exhausted.
• Historically copper was smelted, but modern production involves dissolving ore in sulphuric acid, then extracting pure copper through electrolysis.
• Copper can be toxic in sufficient concentrations. Combining copper rainwater goods with harvested drinking water is not advised.

Embodied energy

• General copper: 40 - 55 MJ/kg (assumes a recycled content of 46%)
• Recycled copper from high-grade scrap: 17.5 MJ/kg (1)

Design Life

60 + years (2)

Pro Recyclable
Pro Durable
Pro Products can include high levels of recycled material
Pro Corrosion resistant
Con Very limited natural resource
Con High embodied energy
Con Toxic in high concentrations
Con Expensive

• See also 'Copper production & environmental impact'


• Zinc reserves are extremely restricted. Zinc should be specified only where substitutes are not possible.

• See also 'Zinc production & environmental impact'


PVC (Poly Vinyl Chloride)

• PVC is manufactured as follows:
1 Chlorine is extracted from sea salt via electrolysis, and ethylene is derived from hydrocarbon raw materials. These are reacted to produce ethylene dichloride
2 Ethylene is combined with chlorine and oxygen to produce vinyl chloride monomer and water.
3 PVC is made by ' addition polymerisation.' This reaction opens the double bonds in the vinyl chloride monomer (VCM) allowing neighbouring molecules to join together creating long chain molecules.

• There continues debate about the safety of PVC.

Embodied energy

PVC pipe: 67.5 MJ/kg (1)

Design Life

20 - 30 years (2)

Pro Low maintenance
Pro Cheap
Pro Easy to install
Pro Lightweight
Pro Corrosion resistant
Pro Recyclable
Con Concerns over the safety of PVC manufacture and disposal
Con High embodied energy
Con Petrochemical content - non-renewable resource, emissions associated with extraction & refining
Con Vulnerable to damage
Con Colour fading
Con Prone to leak at joints
Con Short life expectancy
Con Very little PVC is recycled

GRP (Glass Reinforced Polyester)

• GRP is a ‘Thermoset Composite’ composed of polyester as the thermosetting polymeric matrix reinforced by fine fibres made from glass.
• The glass fibres, which account for 30% of the content of GRP, are made from sand, soda ash and limestone melted at high temperatures.
• Polyester is a petrochemical product

Embodied energy

100 MJ/kg (1)

Design Life

30 + years (2)


• Wood is the oldest form of guttering. Popular until the 20th century, wood was replaced by cheaper plastic and metal alternatives.
• Wood guttering has the lowest environmental impact.
• To ensure durability, correct choice of wood is vital. Suitable species include Scots pine, Pitch pine, Sweet chestnut and Elm.
• Maintenance includes repainting of the outside and re-oiling of the inside (if no lining) on a regular basis.
• Wood performs best when un-painted. Painting increases drying time after rain.
• Durability can be increased by lining the gutter with single-ply roof covering, bitumen or specialist wood oil.

Embodied energy

General timber: 8.5 MJ/kg (1)

Design Life

70 + years if maintained correctly (2)

Pro Durable if maintained correctly
Pro Negligible environmental impact + timber sequestered carbon dioxide
Con Without maintenance, wood gutters can rot, split and crack
Con Requires expert installation
Con Relatively expensive
Con Very few manufacturing sources (though some branches of Jewsons hold stocks)


1 Inventory of Carbon & Energy (ICE) - Version 1.6a - Hammond & Jones, Univ Bath
2 Building Life Plans

Suppliers of wooden guttering

• Kinsley Timber, Pontefract, W. Yorks, 01977 611369
• Bennetts Timber, Grimsby, Lincs., 01472 350151, sales@bennettstimber.co.uk
• High Tech Roofing N/W, Salford, Lancs., 07729 811594, hightechroofing2004@hotmail.co.uk
• ST Building and Roofing, Sheffield, 0114 265 2055, stbuilders@btinternet.com
• A1 Gutterclean, Sheffield, 0114 268 2894, enquiries@a1gutterclean.co.uk
• Lancaster Woodcraft, Lancaster, 01524 771700, info@lancasterwoodcraft.co.uk
• Sheffield Roofline, 0114 230 3177, www.sheffield-roofline.com


Further information

• Copper Development Association (www.copperalliance.org.uk/)
• UK Steel (www.eef.org.uk/uksteel/default.htm)
• British Stainless Steel Association (www.bssa.org.uk)
• International Aluminium Institute (www.world-aluminium.org)


Rainwater drainage products on GreenSpec



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