Root Barrier Installation
In the UK, root barrier installation is increasingly specified where a physical barrier is needed to block, contain, or direct roots of invasive species, trees and shrubs. The use a ‘Tree Root Barrier’, has become more commonplace, as it has become more widely known the damage that tree roots can cause. The roots of trees, and some invasive plants, can damage structures such as buildings, pathways, and underground utilities.
Root Barrier Applications
Before considering how to install a barrier, the application for root barriers must first be understood:
Using root barrier to block
To physically block roots, it is important to understand the rooting depth of the tree or plant in question. With tree root barrier for subsidence, fibrous roots of tree species are often found 3-4m deep. The process of installing deep root barriers for subsidence will require professional input and will be very different to installing a shallow barrier. For comparison, bamboo, which is shallow rooting, normally with roots present within the first 50cm of soil profile, can be dug by hand without any significant issue.
Using root barrier for containment
Where aggressive or invasive rooting plants need to be prevented from spreading outside their intended growing spaces so they don’t contaminate or damage land. Root barriers can also be used to ensure roots don’t spread outside of someone’s landownership wish is becoming increasingly important in the UK due to litigation against landowners who don’t contain Bamboo, Japanese knotweed and other invasive species concern.
In addition, root barriers are often specified where soils contaminated with invasive plants need to be buried on-site. In this instance, professional advice must be sought on how to install a root barrier, as various forms of legislation and guidance will need to be complied with. The aim of a root barrier cell is to contain soils impacted by invasive species, such as Japanese knotweed, to avoid using landfill sites that are increasingly scarce and costly.
Using barriers to re-direct roots
When planting new trees, it is often desirable to direct roots downward away from foundations, formation layers of pavements, and utilities. A tree root barrier that can direct roots to a soil volume that allows trees to establish and reach their full potential without causing damage to the built environment is generally the objective of a barrier designed as a root director.
Considerations for root barrier installation
The following must be considered when planning a Root Barrier installation:
- Site Assessment: A professional will need to inspect the site to determine the type of root barrier needed based on the soil, slope, and vegetation type.
- Excavation: The area around the structure where the root barrier will be installed must be excavated. This work will involve removing soil and vegetation to create a trench. For deep root barrier installation, temporary ground support may be needed with risk assessment undertaken.
- Installation: The root barrier is installed in the trench, typically dug using an excavator for deep root barrier installation or by hand or using a specialist soil saw for shallow root barrier installation.
- Anchoring: horizontal barriers and root barrier cells may need to be anchored to prevent barrier material from shifting. Consideration must be given to anchoring the barrier without puncturing it.
- Jointing and welding root barrier: For larger installations, the root barrier may be site welded, pre-welded off-site, or joined on-site with adhesive barrier tape or glue. Each manufacturer may have differing requirements.
- Protection: Some manufacturers of root barriers will specify sand bedding of additional fleece, especially if the soil profile contains sharp objects or there is a concern of puncture.
- Incorporation of root barriers into built structures: Specialist guidance on how to install root barrier is important where the barrier is to become an integral part of construction. Root barriers may sometimes be incorporated into foundations, bonded to walls or secured to structures.
- Backfilling: Once the root barrier is installed, the trench is backfilled with soil and compacted to prevent settling. For Deep Root Barrier installation is not uncommon to remove the soil and install an engineering aggregate that can better resist settlement and compaction.
- Monitoring/maintenance: Some plant species will send out roots along the soil surface, so leaving a root barrier protruding above ground or incorporated into finished surfacing is important. Bamboo is known to do this. In this scenario, where a specie can grow on the surface monitoring the root barrier after installation to ensure it remains effective must be undertaken as a post-installation maintenance task.
Types of root barrier
Selecting the right barrier is important it involves considering the material, its durability, permeability, and warranty.
In summary, root barriers are generally made from polyethylene due to its durability and low cost of manufacture.
Barriers will be of different thicknesses, and some will be woven which will have an effect on durability.
Root directors may be permeable or feature nibs to stop root spiralling and better direct roots downward. In addition, composite root barriers which can be permeable will use a copper layer proven to deter root growth.
For weed control and suppression, a lower-grade permeable sheet is often specified, which will only resist annual weeds and less aggressive species.
Cost of root barrier installation
The first cost to consider is that of the root barrier itself. Quality root barrier will cost from £6/M2 for normal low-volume applications.
If a specialist composite root barrier, root director’s roots or permeable root barrier is required, then the cost of the barrier can double or triple. Conversely, weed suppression barriers are more economical, costing £1-£3 M2, subject to quality and volume.
Where additional protection is needed, this can also add to the cost, with sand blinding costing as much as the barrier to supply and install. Protective fleece will cost £1-£3/M2.
The labour and machinery cost for installing a root barrier is generally the biggest cost. As a rough guide, hand digging a root barrier 50cm-60cm will cost £60-£80 per meter of trench. However, if a specialist soil saw or excavator can be used, this cost can potentially halve.
For deep root barrier installation where trenches are greater than 2 metres and where there is a need for temporary works to shore up the trench walls, the cost can easily exceed £1000/metre.
The cost of root barrier installation can vary depending on factors such as the size of the project, the type of barrier used, and the location. Therefore, it is best to gain specialist advice from professionals to understand how to install root barriers while getting an accurate cost estimate.
PBA Solutions are experts at installing root barrier, having put in place solutions for trees and the most publicised invasive species, including Japanese knotweed and bamboo. However, root barrier systems can also provide a solution to regain land taken over by less publicised plants that can also be invasive, such as Staghorn Sumac.
We listen to your circumstances, assess the location, then specify and design route barrier solutions tailored to meet your needs. This service is offered throughout the UK and is backed by, PBA Solutions, accredited invasive weed specialists and professional arboriculturists. Call 0203 174 2187 or 01202 816134 to talk to one of our consultants today.