Plastic pipes are better for the climate than metal pipes

An EPD in itself does not cut emissions

Since 2021, the research project Green Plumbing has looked at the greenhouse gas load associated with plumbing installations and possible solutions to reduce the footprint. In 2021, there were very few environmental declarations (EPDs) for plumbing products, which are necessary to assess the environmental impact of products and solutions. However, in recent years, development has been rapid and the fact that a product has an EPD has become a competitive advantage.

However, an EPD in itself does not result in any environmental savings. It only tells us the size of a product's footprint for various environmental indicators. In theory, an EPD can be created even for the most environmentally unfriendly product.

An EPD in itself is therefore not proof that a product is environmentally friendly, but only documentation of the environmental impact. It is only when the EPDs are used to compare and optimize products and solutions that they provide an environmental effect. The industry has the purchasing power to choose the products that have the lowest environmental impact, and can thus shift the competition to environmental performance.

Environmental organizations work for less use of plastic

The use of plastic in the construction industry is increasing and we surround ourselves with plastic in the built environment every day. For Norway, it is estimated that about 180,000 tons of plastic are placed on the market annually, excluding packaging (from the report Plastic Recycling in Construction and Infrastructure in a Circular Perspective, 2023).

In 2022, FutureBuilt launched a separate set of criteria for plastic use in construction, for projects that want to drastically reduce plastic use. Some of the biggest challenges with plastic are stated to be the use of fossil resources, pollution, waste production and the production of chemicals that are hazardous to health and the environment. For projects that follow the set of criteria, all plastic used must have a technical or functional purpose, and should only be used where there are no alternatives with a lower environmental impact.

Pipe production accounts for the largest greenhouse gas emissions

When comparing pipe qualities, it is important to distinguish which areas of use they are relevant for. Furthermore, all significant properties and intended functions should be highlighted and taken into account as far as possible. Examples of this are liquid volume, insulation, sound insulation and clamping. All studies that Multiconsult (formerly Erichsen & Horgen) has conducted show that it is the actual production of the pipes that accounts for the largest emissions. Other technical details such as suspension type, clamp spacing, and the use of fire collars (plastic pipes) or fire sealing (metal pipes) for penetrations are of less importance.

In a master's thesis associated with Grønn VVS (Stenberg, 2023), emissions for different combinations of plastic and metal drain pipes were compared for a case building. Here, emissions related to the pipes themselves, sound insulation and suspension were compared. Plaster casing for sound reduction accounted for only 0.5 to 5 percent of the total for the different scenarios, while clamping accounted for 5 to 18 percent. The paper indicates that clamping in particular may be of importance in terms of greenhouse gas emissions, but more research is needed to confirm the findings.

Large differences in greenhouse gas emissions

In the diagrams in this article, greenhouse gas emissions related to the production of different pipe grades are compared, for four different applications. In each case, a widely used dimension has been chosen. The relationships between the bars are somewhat different for other dimensions, but the ranking is the same. In general, there is a clear relationship between emissions and weight, with metal pipes being heavier and accounting for greater greenhouse gas emissions than the lighter plastic pipes.

For polypropylene (PP) drainage pipes, EPDs exist for several products with varying greenhouse gas loads, which are illustrated with bars for the lowest (min) and highest (max) emission levels. For the other material grades, there are few EPDs and each bar represents a single EPD. Product-specific EPDs have been used, with two exceptions. For galvanized steel pipes and copper pipes, generic EPDs have been used in the absence of these. The focus of the article is on material grades and manufacturer names have therefore been omitted.

The diagrams only show greenhouse gas emissions related to the production of pipes, with one exception for cast iron drain pipes (better known as MA, sleeveless drain pipes). The EPD for MA pipes also includes pipe fittings and suspensions, which to some extent contribute to higher emissions in the comparison. In particular, for plastic drain pipes, additional sound insulation may be needed. This is not taken into account in the comparison and constitutes some uncertainty, but preliminary calculations indicate that it does not make a major difference.

Thermal insulation and condensation insulation are not included and must be assessed project-specifically. Insulation has a low specific weight and typically amounts to little compared to the pipes themselves. Clamping can affect the total emissions when choosing pipe quality somewhat, but preliminary calculations indicate that it would not change the size ratio and ranking significantly if it had been included.

* EPDs are prepared in accordance with standard EN 15804. In 2019, significant changes were made that came into force in July 2022. It is most correct to compare only EPDs prepared according to the same version, but since there is a limited selection of EPDs, EPDs according to both versions are included. Those according to the old standard (EN 15804+A1) are marked with an asterisk.

For heating and cooling systems, plastic pipes have significantly lower greenhouse gas emissions than Alupex and steel pipes. For drinking water and sewage pipes, the trend is also that plastic grades have lower greenhouse gas emissions than Alupex and metal pipes, but for drinking water, copper pipes are the most emission-intensive alternative. For sewage pipes, cast iron comes out worst, but there are also large differences between different plastic materials and between different PP products. Note that the EPD for cast iron, unlike the others, also includes pipe fittings and suspensions, which contribute somewhat to the difference. The plastic pipes may also entail additional costs for sound insulation. Current research suggests that both factors are not enough to change the fact that cast iron comes out significantly worse than the plastic alternatives.

Skipping over other environmental indicators in the EPDs

Greenhouse gas emissions are only one of 13 mandatory environmental indicators that are often stated in EPDs. These include eutrophication (regrowth), resource depletion, acidification, water consumption and ozone impact. In addition, there are six optional indicators that can be included, which deal with particle emissions, radiation, toxins and soil quality.

To understand the overall environmental impact of pipes, it is obviously not enough to look only at greenhouse gases. However, current practice for LCA analysis of buildings is usually limited to this. In R&D Green Plumbing, the focus is on greenhouse gas emissions, but we clearly see that more research is needed on other environmental impacts as well. The plumbing industry can lead the way in the construction industry by focusing on this.

Plastic (pipes) going astray?

One of the biggest problems with the use of plastic in society in general is when it goes astray as microplastics. Unfortunately, much of this ends up in nature and causes problems for the organisms that live there. Traces of plastic are constantly appearing in unexpected places, where it should not be. Plastic in the ocean and in marine animals is perhaps the most well-known problem, but plastic has also been found on mountaintops, at the poles, and in us humans. The question is whether the increased use of plastic pipes also contributes to the problem?

On construction sites, plastic is used within limited areas with strict requirements for waste management. But what happens to the chips from sawing pipes, when wind or rain carries small parts out of the construction site, or when pieces of plastic get stuck under the shoes of the craftsmen?

The extent to which the use of plastic pipes contributes to the spread of plastic in nature is not known, but there may be mitigating measures such as better vacuuming and more use of prefabrication. The plumbing industry must acknowledge that we do not know enough about how our use of materials contributes to the spread of plastic. There is clearly a need for more knowledge and preventive strategies should be implemented to minimize plastic waste.

A challenge for suppliers

The plastic challenge requires our focus and that all plumbing players take responsibility for their contributions. For example, suppliers should ensure increased knowledge about their products, optimize production and provide information on solutions for reducing the environmental footprint. One of the challenges that must be addressed is the use of chemicals in production. It has been documented that plastic can leak additive chemicals into the environment throughout its lifespan, and that this can negatively affect the environment. Initially, this is regulated by the substitution obligation, which states that companies that use hazardous chemicals are obliged to consider whether alternative substances are available.

Another major challenge with plastic is waste management. There are many technologies for recycling and chemical recycling of plastic, but a recent report published by the Center for Climate Integrity (The Fraud of Plastic Recycling, 2024) states that these do not work sufficiently, are not scalable enough, or are too energy-intensive. And in order for plastic pipes to be recycled, it must be possible to separate the pipes from the rest of the construction waste.

Multiconsult largely recommends the use of plastic pipes in buildings, but this assumes that they can be separated at the end of their service life. When it comes to embedded plastic pipes, it can be argued that there are not good enough solutions for waste management today. This is a cross-section of thoughts that should be explored further and can influence our choices for new buildings. Nevertheless, solutions must be found for when all the embedded pipes in the existing building stock will one day be demolished.

In addition to emission-reducing measures in product design and in factories, long service lives and reuse are effective means of reducing the footprint, and for more indicators than greenhouse gases. There are bio-based plastic products, but for now on a small scale and this only solves part of the plastic challenge.

Other measures can be fossil-free production, an increased proportion of recycled material, better utilization of the technical service life and lower specific weight for the products. Emission-reducing measures can also be taken for metal pipes, which reduce the difference to plastic pipes. The research community wants more product-specific EPDs for metal pipes.

The best option today, but we are not there

Overall, we should use fewer and smaller pipes where possible. But the need for new pipes will still be there, both in necessary new buildings and for replacing pipes that have reached the end of their service life in the existing building stock. There will therefore also be a great need for new pipes in the future. But the need can be reduced, among other things through optimal design of routing paths, prefabrication, good system solutions, and by careful and correct dimensioning for each individual project. A technical and professional overall assessment should always be made of which pipe qualities are suitable for each individual installation and not all pipe qualities are always relevant.

Plastic pipes account for lower greenhouse gas emissions than metal alternatives, but are not problem-free. They also have greenhouse gas emissions and we know too little about other environmental impacts. Therefore, the use of plastic pipes is not sustainable in itself. But the trend is still clear - if you want to reduce greenhouse gas emissions for pipes, you should choose plastic over metal.

The goal is sustainability in the true sense of the word, climate neutrality, and that we can produce the pipes we need without negative environmental impact. The road to get there is still a long one and will present many twists and turns. A knowledge boost is necessary, and we only have time and the road. Until better research is available, our conclusion is as follows:

We should limit the use of materials as far as possible, and when pipes are needed in buildings, they should be made of a material with the lowest possible negative environmental impact over their lifespan. Based on what we know today, this pipe material is made of plastic.

Further information about Green HVAC

Green Plumbing is an Innovation Project in the business sector, supported by the Research Council of Norway. The project was carried out in the period September 2021 to March 2025.

Project objectives: Building competence, developing new services and sharing knowledge. Showing the way to a 50% reduction in greenhouse gas emissions from HVAC installations in model projects

The project manager is Multiconsult. Partners in the project are Höegh Eiendom, GK, Armaturjonsson, Swegon, KLP Eiendom and Pipelife. R&D supplier is OsloMet. The reference group consists of VKE and FutureBuilt.