Cast iron – Expensive or the lowest lifecycle cost of all rainwater goods?
Rainwater systems provide a vital function in the preservation of a building, extending its longevity and structural integrity. The effect of missing, fractured or faulty guttering is to allow rainwater to attack the wall structure, potentially washing out mortar joints, allowing rainwater ingress and increasing the potential for frost damage. Many common maintenance issues, e.g. internal damp, dry rot, re-pointing, can be traced back to faulty rainwater goods.
Historically wood, lead, cast iron and to some extent copper, were the materials commonly used. Since 1950 plastics, and in particular PVC, have come to dominate the market. On the face of it, plastics appear to offer many advantages over metals, in that they are comparatively light weight, easy to install, apparently maintenance free, and have a lower capital cost. However, when considering what to choose for your own rainwater system you might be surprised to know that the old product is still the best, particularly when you look past the upfront costs.
In recent years cast iron has come back into fashion as doubts emerge over the efficacy of PVC and people look for more sustainable solutions. There are real benefits of cast iron rainwater goods when looked at from ecological and sustainability aspect. In addition to the environmental benefits of cast iron gutters, pipes and soil goods you can also take the following into consideration when making your choice about which system to use:
Cast iron provides:
- Excellent strength and durability – Cast iron gutters and pipes are highly resistant to distortion caused by accident or vandalism. Cast iron gutters are able to withstand the weight of ladders for roof maintenance and cast iron gutters will not bend and sag when subjected to snow or storms.
- Long life – Correctly installed and maintained, cast iron rainwater goods should be expected to last in excess of 100 years. The long life makes cast iron a cost effective choice for rainwater goods.
- Quiet in operation – Cast iron benefits from low noise levels due to the sound deadening properties the material offers. There is very little expansion and contraction, therefore no noisy clicking and creaking. The weight of the castings also help the gutters to sit correctly in their brackets so you don’t get the rattle in high winds that you do with other materials.
- Appearance – Cast iron offers a unique appearance and provides an aesthetic that is the envy of other materials. Whether you choose a common half round profile or a detailed bespoke hopper head, each piece is unique and contributes to the appearance of your home. Cast iron is often copied but never bettered and you may ask why plastic guttering suppliers are trying to replicate cast iron with their cast iron effect guttering, yet you will never see cast iron foundries trying to get their rainwater and soil goods to look like plastic. No other material offers the aesthetic appeal of cast iron, one which can satisfy all the requirements of traditional architecture, making it the logical choice for listed properties, conservation areas and heritage work.
Cast iron rainwater goods
Iron, as a building material, has a long and proud history. Mass produced rainwater goods were first used in the UK in the late 18th century as a cheaper alternative to lead. As such cast iron manufacture has been subject to regulatory control for many years and whilst it cannot be said to be a clean industry practice, experience and regulation serve to ensure that it has become increasingly cleaner year after year.
The vast majority of cast iron rainwater goods produced in the UK are manufactured in small foundries producing less than 5000 tonnes of goods per year. Figures from USA Department of Energy, The Institute of Cast Metals Engineers and UK Iron Foundries are largely in accord as to the energy consumed in the manufacturing process. The technology used, and consequently the energy consumed, can vary across the industry, but a benchmark value for the production of 1 tonne of finished goods of 2200kWh electricity is taken. In addition is the energy (and CO2 content) of the coke used as part of production.
Embodied energy is the energy needed for procuring raw materials, manufacture and transport of the finished products. The total amount of energy needed can be high, considering a compete building if construction, maintenance and repair are included it can account for 20% of the building’s energy use during a 50-year life cycle. Reducing embodied energy in the component parts of a building can reduce its overall environmental burden, and provide pointers to reducing capital cost.
Generally, the more highly processed a material is the higher its embodied energy. Materials of high monetary and high embodied energy value, such as cast iron, are almost certain to have been recycled many times, reducing their life cycle impact.
Materials with the lowest embodied energy, such as concrete, bricks and timber, are usually consumed in large quantities. Materials with high energy content such as stainless steel and cast iron are often used in much smaller amounts. As a result, the greatest amount of embodied energy in a building can be from either low embodied energy materials such as concrete or high embodied energy materials such as steel.
Reuse of building materials commonly saves about 95% of embodied energy that would otherwise be wasted. However, some materials such as bricks and roof tiles may be damaged when reused and it is also important to consider that savings from recycling of materials for reprocessing varies considerably.
Considered over a normal weekly production cycle, where coke is the main fuel source, and including overhead energy consumption, the embodied energy, based on the figures available, is 24.12MJ/kg of finished casting. For the standard house the embodied energy will be 3859 MJ, with embodied CO2 of 275kg CO2.
Cast iron rainwater goods offer unrivalled strength and durability
Cast iron is available in two quality types, grey cast iron and white cast iron. The addition of silicon to the molten iron causes carbon to rapidly come out of solution as graphite. This graphite content offers good corrosion resistance and acts as a lubricant, improving wear resistance. As a result, cast iron rainwater goods have a known life of in excess of 100 years.
Maintenance is deemed to be annual painting, and while this provides added corrosion protection its principal function is aesthetic.
Post-consumer recycling in the iron and steel industries is a well-established practice. Back in 2005 the USA automotive industry recycled 100% of its iron and steel usage, due mainly to the reduction in the amount of steel used in manufacture. Iron foundries typically use 70% to 80% recycled material. This is made up of primary scrap – off-cuts, rejects, etc. from the casting process and bought in scrap. A proportion of new material, pig iron, is necessary to the manufacturing process but the proportion of scrap used at any one time is largely dependent on the state of the scrap market.
The use of this high level of recycled material is a function of the recyclability of iron. It can be melted and re-cast an almost infinite number of times with no degradation and benefits from the well-established nature of the scrap metal industry.
It is clear that the performance of the traditional material, cast iron, outstrips the more modern materials, in the long term. Whilst the initial capital cost is higher cast iron rainwater gutters and pipes are considerably cheaper over the life of the building. Cast iron rainwater goods also have a significantly lower impact in terms of energy consumption and CO2 emissions. There is a good deal of controversy over the emissions and waste from PVC manufacture.
The notion that cast iron guttering and soil products are the more sustainable option is borne out by empirical evidence. High grade buildings of over 100 years old tend to use these materials for rainwater goods and those systems are still in place and functional. Cast iron rainwater and soil products are 100% recyclable and have well established post-consumer recycling facilities.
Aluminium is catching up in this respect but the coatings used on aluminium rainwater goods tend to mitigate against 100% recycling. There is little evidence of any movement towards post-consumer recycling of PVC, and the leaching of toxic waste from landfill PVC is considered a long term problem.
In terms of maintaining the structural integrity of the building cast iron is less prone to failure. PVC is adversely affected by lateral expansion and contraction, and tends to crack or distort joints. It is this effect that has the major impact on its longevity and aluminium systems tend to fail with oxidisation build up in the joints, causing them to leak.
It is therefore sensible to conclude that cast iron rainwater goods not only perform better over the life of a building and offer the greatest potential to extend that life span whilst offering the benefit that they also cost considerably less over the full life cycle.