Buying a house with a private drainage system
Buying a new house is likely to be the largest purchase you will ever make, and it can get very confusing when you start weighing up advantages and disadvantages between your shortlist of properties!
Most properties in the UK are connected to a public mains sewer which collects effluent from the foul drains and conveys it to a central sewage treatment works for processing. However, particularly in rural areas, some properties have private drainage installations because the public main sewer is not available nearby. There are two main types of private drainage, which may be shared with adjacent properties, and may sometimes be located on an adjoining site. These are septic tanks and cesspools, the latter often being referred to as cesspits. Much less common, but becoming increasingly more so, are self-contained treatment plants. Each of these installations must be located such that there is no risk of contamination of watercourses or wells nearby.
Private drainage systems are necessary for any property that is unable to connect to a main drain. Connections to a main drain depends on the location of the drain, and how far you would need to excavate within a highway to get to that drain. You will also need permission from your local water authority to connect, and from your local council to excavate on their land.
Having your own private drainage system means that you are responsible for maintaining it. If you neglect to keep it serviced and emptied (de-sludged), which could result in discharging untreated effluent into the ground or a watercourse, you will be liable for a fine from the Environment Agency. Don’t be put off, however, if you do fall in love with a house that has its own sewage treatment system, septic tank or cesspool. With the correct maintenance, these systems should work for many years without any problems.
As the name suggests, a sewage treatment system is a system to provide full treatment of incoming sewage to a level that the treated effluent discharged is suitable to go directly into a watercourse such as a ditch, stream, culvert, etc. The process of treating the sewage differs slightly between the various types of treatment system, but essentially the sewage enters the system and is treated by bacteria inside the tank, with the solids that cannot break down settling into a sludge at the bottom. The resulting treated liquid waste is then discharged out of the system. This sludge builds up over time and requires periodic emptying by a licensed waste removal contractor. Most sewage treatment systems require some form of power, either for a motor that rotates media discs inside the system, or an air blower that aerates the sewage. Many systems also come with a control panel and alarm, which means that there are moving and working parts that need to be checked annually by a qualified engineer.
A septic tank is designed to connect to a soakaway/drainage field, which is a connected series of slotted pipework constructed underground. The sewage enters the tank - which is usually a classic 'onion' shape or a more cylindrical shallow-dig style - and the solids settle to the bottom. The liquid rises to the top, making contact with oxygen which starts to break down the organic matter biologically. The liquid still contains sewage, but in small enough particles to be carried through the discharge outlet and into the soakaway. The liquid travels along the soakaway and drains into the soil for further anaerobic treatment. Although a septic tank contains no moving parts, and therefore does not require servicing, you will still need to organise to have it emptied (de-sludged) by a licensed waste disposal contractor. You will also need to conduct a percolation (porosity) test to check that your soil conditions are suitable for the liquid to soak into. Failure to do this could mean that your soakaway fails and backs up into the tank, which will mean having to replace it entirely.
A cesspool is simply a storage tank for all sewage, including both solid and liquid waste. There is no discharge outlet and no treatment - you simply have to organise a licensed waste disposal contractor to empty the cesspool on a regular basis. As there is no discharge, cesspools can fill very quickly and need careful monitoring to ensure they do not overflow. Regardless of the system that is already in place, it is important that you ensure that the vendor(s) have kept records of maintenance carried out over the months or even years that it has been installed. Your solicitor is likely to request this information from them - aside from having the correct documentation so you can be confident the system has received the appropriate maintenance, the Environment Agency ask that records are kept for reference if there were ever a discharge issue in the future.
You should also consider that the treatment system currently in place is highly likely to have been sized for the number of bedrooms that the property had at the time. If you plan to extend the property in the future, it is therefore very important that you check that the system will be able to cope with the extra sewage. For this, you will need to ascertain the make and model of the system. This should be on any documentation from when the vendor(s) purchased the system, or on any maintenance sheets from when it has been serviced or emptied.
Finally, if you get the opportunity to take a look at the system and it appears neglected, the covers looks damaged or there is an unpleasant smell, this could point to problems. It is always worth getting the system assessed to ensure that it is in good repair, because the cost of replacing a sewage treatment system can run to several thousands of pounds when you factor in supply, installation and commissioning.
Anglian Home Surveyors are leading building surveyors in Cambridge and Haverhill, and assessing drainage systems is included within our building surveys. If you’re considering buying a property with a private drainage system and you’re at all concerned about any aspect, why not call us on 01223 661439 to commission a building survey?
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