Do you need planning permission for a sewage treatment plant?
Replacing a septic tank is usually permitted development, but building regulations still apply and some sites need consent. Here is what applies when.
Read the guideTwo or three houses on one septic tank is common off the mains. Here is who the rules hold responsible, who pays for emptying, and what to agree in writing.
Everyone whose foul water goes into a shared septic tank is an operator of it, and the General Binding Rules hold operators jointly responsible for the discharge. Unless the deeds say otherwise, costs are normally split between the households using it. Get the split, the emptying interval and who calls whom agreed in writing before anything goes wrong.
Off the mains, a septic tank serving more than one house is an ordinary arrangement. A farmhouse was split into two cottages; a row of three estate properties was built around one tank; a barn was converted and plumbed into whatever the main house already had. None of that is irregular, and plenty of these systems have run quietly for forty years. The trouble starts when something fails, or when someone sells, and nobody can produce a piece of paper saying who is responsible for what.
That is worth sorting out while everything is working. The households are usually on good terms, the cost of agreeing something is nothing, and the alternative is having the conversation while effluent is standing in somebody's garden.
The General Binding Rules for small sewage discharges in England are written around the operator of the discharge. The important point for a shared system is that the term is not limited to one person. If your foul water goes into that tank, you are an operator of it, and so is every other household connected to it. Responsibility is joint rather than divided into shares.
In practice that means the Environment Agency is not going to work out which household caused a problem. If a shared tank is discharging where it should not, or has not been maintained, that is everyone's problem at once. It also means you cannot opt out by pointing at the neighbour whose land the tank sits in. There is more on what the rules actually require in our guide to what the General Binding Rules actually mean for you.
The same logic applies to the upgrade trigger. A septic tank that discharges to a ditch, stream or any other watercourse has to be replaced or upgraded to a treatment plant, and it must be resolved when a property is sold. A shared tank is not exempt. It simply makes the job a conversation between households rather than a decision one owner takes alone.
Before anyone discusses money, somebody should read the deeds. Properties that share drainage very often already carry the answer, in one of three forms:
The first two settle the argument. The third is the one that needs work, and it is more common than people expect. Where there is nothing, the households are free to agree whatever is sensible between them, and the sensible thing is to write it down.
It does not need a solicitor to start with, though it is worth having one tidy it up if the properties are likely to change hands. What matters is that four things are settled before they are tested:
We will invoice each household separately for its share of a visit if that helps, which takes away the most common source of friction - one neighbour permanently out of pocket and chasing the others.
A tank sized for one house that now takes three is doing three times the work. Solids accumulate at the rate they arrive, not at the rate the tank was designed for, and a shared system emptied on the interval it had as a single dwelling will be chronically overdue. If the sludge is reaching the outlet, solids are carrying over into the drainage field, and that is how a cheap job becomes an expensive one.
Signs are the same as on any tank, just earlier and more often - slow drains across more than one property, smell near the tank, grass greening over the drainage field. Those are covered in six signs your septic tank needs emptying, and the interval question in how often should a septic tank be emptied.
One practical point on access: a shared tank is often in the least convenient place of the three properties, behind a gate belonging to a household that is out at work. Our tanker needs to get within hose reach, and the arrangement should say who makes sure the gate is open on the day. Our septic tank emptying page covers what we need to get to a tank.
With one household the cause of a problem is usually obvious. With three, the first job is to stop guessing. A blockage between one house and the tank is that household's pipework; a blocked tank outlet or a failed drainage field is everyone's. The distinction matters because it decides who pays, and it is not something to settle by argument when a camera will answer it in an hour.
That is what drain tracing and CCTV is for on these systems. Unrecorded runs are the norm on properties that were split decades ago, and plenty of shared tanks turn out to have a fourth connection nobody knew about - an outbuilding, a converted stable, or a neighbour further along who has been discharging into it for years. That changes both the loading and the list of operators, so it is worth knowing.
Drainage is now a standard enquiry in every sale, and shared drainage attracts more questions than a private tank, not fewer. A buyer's solicitor will want to know what the system is, where it is, who maintains it, what it costs, and whether there is any written agreement. If the honest answer to the last one is "no", that is usually the point at which forty years of goodwill has to be turned into a document at short notice.
It is also the point at which the upgrade trigger bites, if the tank discharges to a watercourse. Our guide to what the solicitor will ask goes through the paperwork to have ready, and septic tank or sewage treatment plant explains which one you actually have, which is the first thing you will be asked.
If you have just realised you are on a shared system and nothing is written down, the order that saves the most money is: read the deeds, find out what the system actually is and where everything runs, agree the interval and the split, and put the next empty in the diary. None of that is expensive. All of it is far cheaper than the version where the first conversation happens with a tanker on the drive and a neighbour disputing the bill.
If you are not sure what you have or how many properties are really connected to it, call 07884 111 641. We cover Chesterfield, Derbyshire, Sheffield, north Nottinghamshire and Yorkshire, and we would rather look at it on a Tuesday than at midnight.
Ownership and responsibility are two different things, and they often sit with different people. The tank itself usually belongs to whoever owns the land it is buried in, which may be one household, a shared strip, or occasionally neither of the houses using it. Responsibility for the discharge is wider: under the General Binding Rules anyone whose foul water enters the tank is an operator of it. So you can be responsible for a tank you do not own, and your deeds are the only place that settles who maintains it.
It is a civil matter between you, not something the Environment Agency will arbitrate - and the rules will still treat you both as responsible for the discharge in the meantime. In practice the deeds are the starting point, because a maintenance covenant or a shared drainage easement is common on properties like these and it says how costs are apportioned. If there is nothing, a written agreement between the households now is far cheaper than the alternative later. We are happy to invoice each household separately for its share of a visit, which removes one of the usual arguments.
Almost always, yes. A tank sized for one house and later connected to two or three is doing two or three times the work, and the solids build up accordingly. The interval is set by how much the tank actually receives, not by how many years it has been since the last visit. If a shared tank is being emptied on the same schedule it had as a single-house tank, it is overdue.
Sometimes, and it is worth asking the question if the relationship has broken down or one household is about to sell. It depends on whether there is ground for a second tank and drainage field, what the percolation test says, and whether the pipework can reasonably be separated. It is a proper installation job rather than a modification, so it needs looking at on site before anyone promises it is possible.
The seller. The rules require a septic tank discharging to a watercourse to be replaced or upgraded when a property is sold, and a shared system does not escape that - it simply means the households have to agree who arranges and funds the work. Buyers' solicitors now ask about shared drainage as standard, so an undocumented arrangement tends to surface at the worst possible moment.
Septic tank emptying, installations, servicing and drainage across Derbyshire, Sheffield and Yorkshire — 24/7.
Replacing a septic tank is usually permitted development, but building regulations still apply and some sites need consent. Here is what applies when.
Read the guideOff-mains drainage now comes up in every sale. The questions the buyer’s solicitor asks, and the paperwork to have ready before you list.
Read the guideIf your septic tank discharges to a ditch or stream it must be replaced or redirected. What the General Binding Rules require and when they bite.
Read the guide