Installing underground ducting might sound like a job reserved for utility companies and contractors, but whether you’re managing a commercial site or planning domestic upgrades, knowing how to do it properly is invaluable. It’s not just about digging a trench and dropping in some pipes – underground ducting in the UK is governed by legal standards, colour codes, material specifications and depth requirements.
Let’s walk through the process step by step, so your installation is both compliant and built to last.
What Is Underground Ducting For?
Before we get into the installation process, it’s worth clarifying the role of ducting. Underground ducting protects services such as electricity, water, telecoms and gas. It also makes maintenance, upgrades or replacements easier and safer.
A properly installed ducting system will also serve as a visual warning to anyone digging in future – potentially preventing serious injury or service outages.
Further information to help you safely plan and carry out this type of work can be obtained from Street Works UK and the Health and Safety Executive (HSE) – we have included some useful links at the end of this article.
Installation: A step-by-step guide
Plan the Route
Identify Existing Utilities
You should never begin any excavation work without first checking what’s already buried. Utility maps from service providers, local authority records, or a cable avoidance tool (CAT scanner) can help locate existing infrastructure.
Choose a Practical Route
The safest ducting runs follow obvious and accessible paths – along boundaries, driveways, or existing pathways. Avoid crossing other utilities or placing ducting where future access would be difficult.
Where the route requires bends, keep them as gradual as possible. Tight turns make it harder to thread cables or pipes later. Where changes in direction are necessary, plan to install access chambers or use pre-formed, long-radius bends.
Choose the Correct Ducting Colour and Material
UK Utility Ducting Colour Codes
In the UK, different services must be enclosed in different coloured ducting. This is a legal requirement under the National Joint Utilities Group (NJUG) guidelines. Here are some common examples:
- Electricity – Red
- Water – Blue
- Gas – Yellow
- Telecoms and Fibre Optics – Grey or Purple
- Street Lighting – Orange
- Motorways communications – Green
Following the correct colour coding helps ensure site safety and compliance with UK regulations. For full details, NJUG’s Volume 1: Guidelines on the Positioning and Colour Coding of Underground Utilities Apparatus is an authoritative source.
Utility Ducting Material
Utility ducting is typically made from high-density polyethylene (HDPE), unplasticised PVC (uPVC), or polyethylene (PE). Your choice should depend on the installation environment and length of run.
For short runs
Rigid 6m lengths of uPVC or smooth-walled HDPE ducting are ideal for short runs. These offer easy handling and straight-line placement for smaller projects, such as connecting a new outbuilding.
For long runs
For longer runs, we recommend using 25m or 50m coils of flexible PE or twinwall HDPE ducting. Twinwall designs have a smooth inner layer and a corrugated outer wall for strength and flexibility, helping them follow terrain variations.
For heavy loading areas
For installations under driveways or roads, ducting must have a high compression strength – look for options rated SN6 or 450kN. Electric cable ducting should comply with BS EN 61386, which covers three classes for different voltage ranges and conditions.
Always check with the relevant utility provider if you’re unsure which type to use.
Confirm your Legal Depth Requirement
Minimum burial depths vary depending on the utility type and its environment. According to Street Works UK, here are standard recommendations:
| Utility type | Minimum depth (footpath) | Minimum depth (carriageway) |
| Low voltage electricity | 450 mm | 600 mm |
| High voltage electricity | 600 mm | 750 mm |
| Water | 750 mm | 900 mm |
| Gas | 600 mm | 750 mm |
| Telecoms | 250 mm | 350 mm |
In agricultural land, these depths may increase further; up to 1200mm in some cases to avoid interference with machinery. Water pipes at shallower depths must be insulated to prevent freezing.
Failing to meet these standards can lead to penalties or dangerous consequences, so when in doubt, consult local building regulations or your utility provider.
Install the Ducting
Safety First
Always Switch Off Utilities. If you’re working near live services, switch them off wherever possible. Contact the providers if you’re uncertain about procedures.
Mark and Excavate the Trench
Once your route is planned and the utilities are confirmed, mark the trench line. Whether you’re digging by hand or with a mini-excavator, proceed with caution – unexpected services can still appear.
Remove rocks and sharp objects from the trench base, then add a 50mm bedding layer of fine sand or pea shingle to protect the ducting from abrasion.
Lay the Ducting
Place the ducting along the trench bed, following your planned route. Make sure joints are secure and watertight.
- Rigid uPVC is usually socketed for push-fit connections
- Flexible coils often include a coupler at one end
- Twinwall ducting requires purpose-made couplers to join lengths.
Avoid forcing bends tighter than the duct’s minimum bend radius — especially important when cables are to be pulled through later.
Add Marker Tape
Before backfilling, lay a coloured marker tape (matching the utility colour and generally printed with the name of the utility) 150mm above the ducting. This provides a warning for future excavations.
Backfill the Trench
Backfill in layers using suitable material:
- 100mm of fine fill (e.g. sand) over the ducting
- compacted soil or appropriate granular fill, ensuring the ducting stays in position
- surface restoration – turf, gravel, concrete or tarmac as needed.
Update Plans and Records
Once the installation is complete, update any property plans with the new utility routes. This will make future work easier and reduce risks for others.
When in Doubt, Seek Advice
Poorly installed ducting can create future hazards, invalidate insurance and lead to fines. If you’re unsure at any point, consult a qualified installer or the relevant utility provider.
Further Reading
Best Practice Guidelines, Street Works UK
Outlines initiatives to improve street works standards across the UK.
HSG47: Avoiding Danger from Underground Services, HSE
Provides advice on how to reduce risks when working near underground services.
Guidelines on the Positioning and Colour Coding of Underground Utilities Apparatus, NJUG
Detailed recommendations on the positioning and colour coding of underground utilities.
https://streetworks.org.uk/wp-content/uploads/V1-Positioning-Colour-Coding-Issue-8.pdf
BS EN 61386, BSI Group
British Standard specifying requirements for conduit systems used in cable management.
https://landingpage.bsigroup.com/LandingPage/Series?UPI=BS+EN+61386
Written by
Bob Stone
Technical Sales
Heading up our Technical Estimating Department, Bob is our in-house quantity surveyor.
