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 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.
A septic tank that discharges to a watercourse — a ditch, stream, river or surface water drain — is no longer allowed. It must be replaced with a sewage treatment plant or redirected to a proper drainage field. A septic tank discharging to a drainage field is generally still fine, provided it is in good order and properly maintained.
England’s small sewage discharges are governed by what the Environment Agency calls the General Binding Rules. They are not a licence you apply for — they are a set of conditions. Meet them and you can discharge without a permit. Fail them and you need to fix the system or apply for a permit, which for a domestic property is rarely the easier route.
Most of the rules are common sense: the system must be properly installed, it must be maintained in line with the manufacturer’s instructions, it must not cause pollution, and it must be emptied by a registered waste carrier. The one that catches people out is the rule about where the treated liquid goes.
A septic tank may discharge to ground, through a drainage field. It may not discharge to a watercourse. That includes a ditch, a stream, a river, a pond, a land drain or a surface water sewer — whether or not that ditch has water in it most of the year.
The reason is simply that a septic tank does not treat sewage to anything like the standard needed to put it into open water. It separates solids and lets the ground finish the job. Take the ground out of the equation and you are discharging barely treated sewage into a watercourse.
If your tank discharges to a watercourse, there are two legitimate fixes:
Which one makes sense depends on your ground, your space and your budget. Heavy clay with no room for a field points towards a treatment plant. Free-draining ground with a suitable area available often makes a drainage field the cheaper answer.
In theory the requirement has been in force for years. In practice, most households discover it at one of three moments.
When you sell. This is by far the most common. The buyer’s solicitor asks about the drainage, the seller has to disclose that the property is off mains and describe the system, and a discharge to a ditch comes straight out in the answers. Sales get held up at exactly the point where nobody has time to be held up, and the cost usually ends up being negotiated out of the price.
When something goes wrong. A failed system that is visibly polluting attracts attention from neighbours, landowners downstream and ultimately the Environment Agency.
When you build or extend. Adding bedrooms adds load, and building control and planning will both want to know where the sewage is going.
When you sell a property with a septic tank or treatment plant, you have to give the buyer a description of the system, its location, and the maintenance it needs. In practice that means the make and type if you know it, where the tank and drainage field are, when it was last emptied and serviced, and any records you have. Being able to hand over a folder of emptying invoices is worth more at that point than any amount of reassurance.
There is a lot of unnecessary worry about this, usually generated by people selling replacement systems. To be clear:
If somebody has told you that your tank is illegal, the first question is always the same: where does the outfall actually go? Until that is established, nobody can tell you what you need.
Plenty of owners genuinely do not know. Old systems were installed before anybody kept records, outfalls get buried, and a pipe that was obvious in 1975 is under a lawn now. We trace the run with drain tracing equipment and a camera, and tell you plainly what you have and where it ends up — which is the only sensible basis for deciding whether you need to spend anything at all.
If the answer is that you do need to change something, here is what a replacement or upgrade involves. If the answer is that your system is fine, we will tell you that instead.
Only if it discharges to a watercourse. If it discharges to a properly working drainage field, it does not. There is no general requirement to replace all septic tanks.
You can sell, but it has to be disclosed, and in practice either the seller fixes it before completion or the cost is taken off the price. Buyers’ solicitors ask directly, and lenders increasingly take an interest.
A treatment plant has a power supply — a blower humming, or something rotating inside. A septic tank has no electricity. If there is a cable running to it, it is a plant.
A network of perforated pipes in trenches of gravel, sized to the ground’s percolation rate, that lets the liquid from the tank soak away and be treated by the soil. It is not the same as a single soakaway crate, and it has to be sized from a percolation test rather than guessed.
The Environment Agency. In practice enforcement usually follows a complaint or a pollution incident rather than routine inspection — but the obligation applies whether or not anyone has knocked on the door.
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 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.
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 guide