02 Apr 2020

Drain strain – and how to avoid it

Making mistakes with a drainage system, mistakes that often only become apparent when the building is complete, can be painful and expensive. Richard Leigh, Development Director of drainage specialist Lanes Group, explains the steps that can be taken to avoid them.


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Adrainage system is one of the first elements of a build programme for a new house – and it is one of the last elements you want to mess with once it is installed.

That is why every effort should be made to get things right the first time. Substandard drainage systems can cause additional cost, annoyance and downright misery for property owners, sometimes for years.

Six things to always get right when installing drains

1. Pipework sizing
The architect, civil engineer and surveyor should agree between them the correct type and diameter of pipework to install. But our CCTV drainage surveys often find pipes are not the right size by the time they go into the ground.

Getting the size and capacity of drainage systems right is critical. If you do not, there is a greater risk of persistent blockages, sewer surcharging (which can cause flooding) and structural failure.

2. Pipe gradient
Drainage systems should be self-cleansing. The force of the water through the system should be strong enough to carry waste out into main sewers. For this to happen, without the support of pumping systems, the pipes have to be installed at the right gradient to allow gravity to do its work.

3. Correct backfill
When drains are installed, the trenches are backfilled with material. If the wrong material is used, or it is not properly distributed or compacted, the drainage pipes can settle over time, causing flat spots. These can result in blockages and sewer flooding. The only solution may be to excavate and re-bed pipes, which is very expensive.

4. Avoid cross-connections
A cross-connection in a drainage system occurs when a surface water and foul water drain are wrongly connected together. This can result in sewage being discharged into watercourses, a mistake that is surprisingly common. Another common mistake is to locate washing machines in garages and plumb them into surface water drains which may lead to wastewater flowing directly into watercourses.

The consequence will eventually be a prosecution by the Environment Agency and a lot of expense in fines, court costs and remedial action. Surface water that is wrongly channelled into foul drains can cause them to be overloaded, causing surcharging and sewer floods.

5. Drainage design
Modern living standards and practices put drains under more pressure than ever before, leading to increased blockage risks. Yet, drainage systems are often installed with inadequate access points, via manholes and rodding points, making maintaining them more difficult.

Different types of pipes have different strengths and weaknesses. Plastic pipes need more bedding. Clay pipes are more susceptible to root ingress. Making the wrong initial choices can lead to problems later.

6. Construction quality
This is, perhaps, one of the biggest elements to get right. Badly installed drainage systems will perform badly. Wrongly fitted bends slow water flows, increasing blockage risks. Badly benched manholes create snagging points for waste material.

Poorly fitted pipes and connectors also result in snagging and open joints that allow root ingress. Badly fitted manholes also allow debris to enter the drain lines, increasing the risk of blockages.

Before you start building...
Ensure you opt for a drainage survey before works start on your site to avoid damage to underground utilities. In Lanarkshire, Scotland, part of a foundation pile from a housing development was unintentionally driven through a main sewer. In this case, the house-builder was lucky due to the steel and concrete foundation pile being cut out from 60m away without having to excavate. Then the pipe was lined again remotely to restore its structural integrity. For self-builders; however, this would have involved demolishing the house – and at great cost to them, as they will be charged to put the problem right.

Four ways to make drainage maintenance pain-free

Getting these aspects of drain design and build right will prevent major drainage problems and costs later, whether it be weeks, a year or even 10 years. Other ways to ensure drainage maintenance is as stress-free as possible include:

1. Future-proof your drains
Make sure the drainage system has the correct hydraulic capacity to meet future demands, especially if you are planning further building work on the plot.

2. Make drains accessible
Installing a manhole costs money. When budgets are tight, it might look like a sensible saving. But, installing a manhole or rodding points now for hundreds of pounds could save thousands later.

3. Carry out a post-works drainage survey
Whether you are installing the drainage system yourself or contracting a groundworks specialist to do the work, carrying out a post-works drainage survey is a very sensible move.

A drainage maintenance specialist has the equipment – most importantly, remote access to CCTV cameras – to examine the drainage system before further building makes remedial work difficult and expensive.

It is not uncommon for items like spikes and stakes to be mistakenly driven into newly installed pipes. Concrete is regularly poured into pipes, either accidentally or deliberately.

Joints in a pipe can work loose because of poor bedding, or through the action of plant machinery being driven over it.

A CCTV drainage survey of both below- and above-ground pipes can establish the extent of problems, and the likely cause of them. While the work teams responsible are still on site and can be held to account. It is another cost. But one that pays dividends if it reveals something is wrong.

4. Record what you have installed Sewers associated with any new homes are adopted by water companies in a process known as a Section 104 Agreement. The property owner must demonstrate the pipes are properly installed and are in good working order. This is usually done by carrying out a CCTV drainage survey.

It makes sense to ensure this survey is as thorough as possible and is then kept as a record of the drainage system installed. This allows future maintenance issues to be understood and quickly shared with a drainage maintenance company. Costs and time taken to solve future drainage problems will then be greatly reduced.

Make sure water treatment tanks meet regulations

All this advice applies equally to off-mains sewage treatment systems, such as septic tanks and small sewage treatment plants.

In addition, it is important to ensure these off-mains systems meet the latest regulations.

For example, since 1st January 2020, regulations called ‘General Binding Rules: Small Sewage Discharge to the Ground’ have not allowed wastewater from a standard septic tank to be discharged directly into watercourses.

For new-build projects, this means the most likely option is to install a small sewage treatment plant that meets BS EN 12566. A septic tank can still be installed if wastewater is then fed into a drainage field that meets BS 6297:2007 or through another treatment process, for example, an ultraviolet filter.

Finally, when installing a septic tank or small sewage treatment plant, consider its location. Placing it close to a road where there is good access will make it easier for a drainage specialist to position a tanker to remove sludge waste and carry out tank cleaning.

Further information....

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