Underground Drainage FAQs: Your Comprehensive Guide

Underground drainage systems are crucial for maintaining the structural integrity of properties and ensuring efficient water management. Whether you're dealing with blockages, installation, or selecting the right materials, understanding the intricacies of these systems can save time, money and effort. Here are some frequently asked questions about underground drainage.

How Do I Unblock an Underground Drain Pipe?

To unblock an underground drain pipe, start by determining where the water is backing up to, as the blockage will be downstream from that point. If the blockage is not far down the drain, a plunger can increase the air pressure inside the pipe and often force the blockage to break up. Create a tight seal around the drain opening before working the plunger vigorously until the blockage is cleared.

If plunging doesn't work, use a drain snake. Insert the snake into the pipe through the nearest access point and feed it until you encounter resistance, which signals the blockage. Rotate the snake to break up the blockage and push it through the pipe, continuing until the snake moves freely.

Once the blockage is broken up, flush the pipe with water using a garden hose. Insert the hose into the drain and run water at high pressure to clear any remaining debris. For stubborn blockages, a high-pressure water jet can be very effective in blasting away blockages and cleaning the pipe walls.

If the blockage persists, check with a pipe inspection camera to identify the exact location and nature of the blockage and confirm that it has been fully cleared. 

You can also use a commercial drain cleaner or an enzyme-based cleaner to break down organic material, following the manufacturer's instructions carefully. Always wear protective gloves and eyewear when dealing with chemicals or sewage. 

If you cannot clear the blockage yourself or if it is severe, call a professional plumber. Regular maintenance, such as using enzyme-based cleaners monthly, can also help prevent future blockages.

Which Material Pipe is Best for Underground Drainage?

The choice of pipe material used depends on various factors, including durability, cost and application.

Plastic pipes are most commonly used in new underground drainage systems. PVC (Polyvinyl Chloride) is popular for its corrosion resistance, light weight and ease of installation. HDPE (High-Density Polyethylene) is flexible, resistant to corrosion, and suitable for various soils.

However, non-plastic pipes also have their advantages. Clay is traditional and highly durable, though heavier and more difficult to install. Concrete is suitable for heavy-duty applications due to its strength. 

How Should Underground Piping Systems Be Installed?

Proper installation is vital for the effectiveness and longevity of an underground drainage system.

This process begins with thorough planning and design, ensuring proper gradients and appropriate pipe sizes.

Excavation follows, where trenches are dug to the required depth and width. A bedding layer of gravel or sand is then laid to support the pipes.

During pipe laying, it is crucial to position the pipes correctly, ensuring that the joints are secure and watertight.

Finally, backfilling involves covering the pipes with selected backfill material, which is compacted in layers to prevent settlement.

What Are the Key Components of a Well-Designed Underground Drainage System?

A well-designed underground drainage system includes several essential components to ensure efficient and effective water management. 

Pipes, made from suitable materials and sized appropriately for the application, form the backbone of the system. Manholes serve as access points for maintenance and inspection, while gullies collect surface water. 

Channels and gratings facilitate surface water drainage, and inspection chambers, which are smaller access points compared to manholes, provide additional accessibility. 

Soakaways are structures designed to manage surface water runoff, completing the comprehensive drainage system.

What is the Correct Depth to Install an Underground Drainage Pipe?

The correct depth for an underground drainage pipe varies depending on the pipe's purpose and location. Domestic drainage pipes are typically installed at a depth of 600mm to 900mm to prevent damage from freezing and surface loads. Main sewers are often deeper, ranging from 1.2m to 1.5m. Surface water drainage pipes require a minimum depth of 450mm, though local regulations may vary.

What Drainage Pipe Sizes Are Used in the UK?

Different pipe sizes serve various purposes. A 110mm pipe is common for domestic waste pipes, while a 160mm pipe is used for larger domestic systems or small commercial properties. Pipes measuring 225mm and above are used in commercial, industrial, and main sewer lines.

What Size Pipe is Right for Domestic Drainage Systems?

For most domestic systems, a 110mm diameter pipe is standard. This size efficiently handles the typical waste output from residential properties and conforms to UK building regulations.

Should an Underground Drainage Pipe be Flat or Sloped?

An underground drainage pipe should always be sloped. A gradient of 1 in 40 (2.5%) is standard for wastewater, ensuring gravity assists in efficient water flow and preventing stagnation and blockages.

Why Are Drains Normally Installed Underground?

Installing drains underground hides them from view, maintaining the property's appearance, while protecting them from physical damage and weather conditions. 

Underground installation also allows for natural gravity flow from all floors of a property except a basement, reducing the need for mechanical pumping. 

What Are the Signs of a Blocked Underground Drain?

Signs that you might have a blocked underground drain include several key indicators. 

Water draining slowly from sinks, showers or bathtubs is a common symptom, as is hearing unusual gurgling noises from your drains. 

Persistent foul smells near drains or outside may also suggest a blockage. 

Water backing up or overflowing from gullies or inspection chambers is a clear sign of trouble. Unexplained damp or waterlogged areas in your garden or around your property can further indicate a blocked drain.

Can Tree Roots Damage Underground Drain Pipes?

Yes, tree roots can penetrate and damage underground drain pipes. They seek out moisture and can enter through small cracks or joints, causing blockages and structural damage over time. Regular maintenance and root barriers can help prevent this issue.

How Often Should Underground Drains Be Inspected?

It's recommended to have underground drains inspected every 2-3 years to ensure they are functioning correctly and to catch any potential issues early. However, if you notice any signs of blockages or drainage problems, an immediate inspection is advised.

What Are Soakaways, and When Are They Used?

Soakaways are underground structures designed to manage surface water runoff by allowing it to slowly soak into the ground. They are commonly used in areas with poor drainage to prevent flooding and standing water. Soakaways are essential for properties without access to a suitable surface water sewer.

What Regulations Govern Underground Drainage Systems in the UK?

Underground drainage systems in the UK are governed by several regulations and standards, including:

• Building Regulations (Part H): Covering drainage and waste disposal.
• Water Industry Act 1991: Relating to public sewers and water authorities.
• BS EN 752: The European standard for drainage systems outside buildings.
• Local Authority Requirements: Additional requirements may be imposed by local councils.

Can I Connect Rainwater and Foul Water Drains?

No, rainwater (surface water) and foul water (wastewater from toilets, sinks, etc.) should be kept separate. Mixing these can lead to environmental pollution and is against UK building regulations. Separate systems ensure efficient treatment and disposal of both types of water.

What Is the Lifespan of Underground Drainage Pipes?

The lifespan of underground drainage pipes varies depending on the material used. PVC, HDPE and clay pipes typically last between 50 to 100 years, while concrete pipes have a slightly longer lifespan, ranging from 70 to 100 years. 

Regular maintenance can help extend the lifespan of these pipes, ensuring their continued effectiveness and durability.

What is the Role of a Gully in a Drainage System?

A gully is a component of a drainage system designed to collect and transport surface water. It typically has a grate on top to catch debris while allowing water to enter the drain. Gullies are commonly used around buildings, driveways, and roads to prevent flooding.

How Do I Prevent Blockages in Underground Drains?

Preventing blockages in underground drains involves a combination of regular maintenance and good practices. 

To avoid issues, refrain from disposing of grease, fats, or oils down the drain, as these can cause significant build-ups. Installing drain guards in sinks and showers can help catch hair and debris, preventing clogs. 

It is also important to use safe drain cleaning products periodically to keep drains clear. Regular inspection and maintenance of both drains and gutters are crucial for early detection of potential problems. 

Managing tree roots by keeping trees and shrubs well away from drain pipes can prevent root intrusion and subsequent blockages.

What Happens If Underground Drains Are Not Properly Maintained?

Neglecting underground drain maintenance can lead to a range of serious issues. Blockages may cause water to back up into your home, leading to potential water damage. It can erode foundations and other structures, resulting in significant structural damage. 

Stagnant water from poorly maintained drains can attract pests and harbour harmful bacteria, creating health hazards. 

Failing to maintain underground drains also increases the risk of severe flooding during heavy rainfall, as the system may fail to effectively manage the water flow.