Tree roots are often cited as the main cause of broken pipes in Sydney’s waste systems. In this article we explore and dispel some of the myths surrounding the reputation of tree roots causing broken pipes. The information provided in this article originates from a paper written by Hartley M (2013), published by the Arborist Network.

Myth 1 – Tree Roots Go In Search Of Water

Contrary to common belief, tree roots do not actively seek out water. They grow and divide in response to available moisture and optimal soil temperature, rather than searching for water when the soil is dry. In other words, root growth is an opportunistic process. An understanding of the mechanisms that drive root growth, namely soil moisture and temperature within the required range for the plant, and to a lesser extent, available minerals, is vital in understanding that roots seldom break pipes and then enter them. In most circumstances, roots enter through joins, cracks and breaks that pre-exist in the pipe work.

Cracks in pipes and the breaking of cement joins and rubber seals are common over time. When a pipe cracks or a joint fails, it begins to leak nutrient-rich, oxygenated water through the cracks into the surrounding soil. If roots come into contact with this favourable environment, they start to grow and divide rapidly to take advantage of the resources. In such cases, it’s only a matter of time before roots reach the crack in the pipe and enter it, often leading to even faster growth inside the pipe.

Myth 2 – Tree Roots Cause Pipes to Break

Tree Roots Crush Pipes

The perception that tree roots break or move pipes is common, but the likelihood of it happening is low. Physics explains this phenomenon: a pipe supported by soil is stronger than an unsupported pipe, and it requires a significant amount of force to crack. A root would have to push the curved pipe inward to cause damage. This is unlikely to happen unless there is a pre-existing defect in the pipe or the outer portion of the pipe wall is compressed. The high load-bearing capacity of baked clay pipes, combined with their curvature and soil support, makes inward failure due to root growth a rare occurrence. The effect of curvature on wall strength is demonstrated by the classic childhood experiment of trying to crush an egg by pushing from both ends.

Tree Roots Cause The Lateral Movement of Pipes

For a root to move a pipe, it would have to push the pipe into the surrounding soil. In soil that doesn’t easily compact, such as sand, the support for the pipe is so strong that the root would have to be wider in diameter than the pipe. In such scenarios, the forces would be so high that cellular division in the root would be significantly hindered in most of the root’s contact area with the pipe, resulting in only the outer zone of the root being able to apply pressure.

In soil that provides less support, such as clay, where it may be possible to push a pipe into the surrounding material, there’s still an equal and opposite force acting on the tree root, which is usually enough to inhibit root growth where the root contacts the pipe. This results in faster root growth on the side away from the pipe, where the root can expand more easily and push the soil around it away.

When Tree Roots Do Cause Damage

It is incorrect to suggest that tree roots never damage pipes. Where roots have a diameter greater than the outside diameter of the pipe, they may produce sufficient force to dislodge a pipe particularly if the soil is regularly approaching plasticity. In addition, roots that enter through a join between pipes can conceivably develop sufficient surface area to move the pipe a few millimetres until it fully beds in at the next join. In the same situation, the volume of roots in the join could develop sufficient surface area so that the outer collar of the pipe is broken, (the inner pipe being protected against breakage as described above). tree root in collar of terracotta pipe

The final way in which roots may damage pipes is where a root is curved around a pipe and that root is subjected to a tensile force in turn pulling on the pipe. The tensile force that is applied to a root is a product of a number of factors including the force applied to the canopy of the tree above ground and the cohesive strength of the soil, the number of first-order lateral roots, the rate at which root division and root taper have occurred. In most cases, the amount of movement in roots is quite small, and the extent of movement diminishes rapidly as the distance from the tree increases. Mattheck & Breloer (1994)

Myth 3 – Cement Joins in Pipes Are Porous

Some plumbers argue that the porosity of cement used to connect pipes attracts roots by allowing water to seep through the joint. Although it’s true that cement is porous, the flow rate is low and the amount of water that passes through is not enough to significantly affect root growth. Even if the cement was exceptionally porous, the slope of the pipe would limit the amount of fluid present at the joint. Over time, the inside surface of the pipe becomes lined with small particles and fatty compounds, further hindering deposits. Additionally, roots cannot penetrate cement, as evidenced by the lack of root penetration in cement pots.

To Reline, Replace or Maintain Broken Pipes

There are 5 ways to deal with damage to pipes from tree roots:

1. Drain Cleaning

Water jet cleaning is preferred over using an electric eel to remove roots from pipes. This is because high-pressure water typically removes more roots while causing less damage to the pipes or joints. It’s important to note that cut tree roots can regrow from the cut ends, leading to recurring blockage problems in the drains.

2. Foam Treatments

To address the issue of tree roots affecting pipes, the plumbing industry has come up with various techniques to limit or prevent root intrusion. One approach is to fill the pipes with phytotoxic foam, which kills the ends of the roots. This method temporarily stops new roots from entering the pipe as the dead roots act as a barrier, but as they decay they create channels for new roots to penetrate. So this is not a sustainable solution unless used with pipe relining.

3. Pipe Relining

Another solution is pipe relining. This method involves inserting the membrane into the pipe and curing it, sealing the entire pipe and reducing the stimulation of root growth. The cured membrane, bonded with the original earthenware pipe, prevents new roots from entering. Relining not only strengthens the original terracotta pipes, but it also seals them with a membrane that is impermeable to water and impenetrable to pioneer roots. The process requires little to no excavation, making it an ideal solution for root problems in existing pipes without disturbing the surrounding landscape.

When relining in areas with high concentrations of roots, there are several factors to consider, such as:

  1. Root assessment: To determine the extent of the root growth and the potential for new root penetration, it is important to conduct a comprehensive assessment of the area.
  2. Pipe condition: The condition of the pipes, including any cracks, corrosion, or damage, needs to be assessed to ensure that relining is the most appropriate solution.
  3. Accessibility: The location and accessibility of the pipes needs to be considered to ensure that relining can be carried out without disruption to the surrounding area.
  4. Quality of materials: The quality and durability of the materials used for relining should be considered, as well as the installation method used.
  5. Installation procedure: The installation procedure should be carefully planned and carried out to ensure that the liner is properly inserted and cured to provide a long-lasting solution.
  6. Cost: The cost of relining versus other solutions, such as replacing the pipes, should be considered in light of the long-term benefits.
  7. Guarantees: The guarantee offered by the manufacturer or installer should be evaluated to ensure that the relining solution provides adequate protection for the expected lifespan of the pipes.

4. Replacing Broken Pipes

The replacement of old terracotta pipes with PVC pipes may seem like the ideal solution. However replacing terracotta pipes can be a disruptive and time-consuming process that requires excavation and access to the affected area. This can lead to damage to surrounding landscapes, buildings, and infrastructure, and also result in increased costs for the homeowner. Relining the pipes with a resin-impregnated membrane provides a guaranteed period of serviceability and can potentially have a longer lifespan. This option is also less disruptive, as it can be done without excavation, making it a suitable method for addressing root problems.

5. Maintaining the Pipes

Just like any other property, pipes have a limited lifespan and require proper maintenance. Neglecting the maintenance of pipes is the main cause of root intrusion. Many terracotta pipes have reached or exceeded their usable life. However, it takes the presence of tree roots to reveal the breaks and faulty joints that are not visible to us, reminding us that maintenance is long overdue. In many cases, roots in pipes serve as a prompt to upgrade them.

Choose the Right Plumbing or Pipe Relining Contractor to Fix Your Broken Pipes

If pipe choosing replacement in areas with a high concentration of roots, it’s best to replace faulty and leaky drains with a well-engineered and designed drainage system. This system should incorporate necessary expansion joints and pipes with appropriate wall thickness and tightly sealed, glued, or welded joints. Equally, if choosing relining, make sure the solution is the right one taking into account the environment. Sectional pipe repair (as opposed to inversion relining) may not be the best solution as tree roots can grow back either side of the pipe repair. Always look for a relining installer who is licensed, with experience and expertise in relining pipes in areas with a high concentration of roots backed by a guarantee.