Do you need planning permission for a septic tank?

Three separate approval regimes apply to septic tanks in England, and people routinely satisfy one while breaching another:

1. Planning permission — may you build it?
2. Building regulations — is it built correctly?
3. Environment Agency rules — is the discharge lawful?

They are administered by different bodies, and passing one says nothing about the others.

Planning permission: usually not needed

For an existing house, installing or replacing a septic tank normally falls under permitted development. The reasoning is straightforward — the tank is below ground and has no visual impact.

Planning permission becomes more likely where:

• The property is listed, or in a conservation area or National Landscape (Cornwall has substantial designated areas, so this catches more properties here than in many counties)
• The installation involves visible above-ground structures — a pumping station housing, a treatment plant kiosk
• It serves a new dwelling, in which case drainage forms part of that application anyway
• It serves a new annexe or holiday let that itself needs permission

If in doubt, ask. A pre-application enquiry to Cornwall Council costs little and settles it. Permitted development is a general rule with real exceptions, and “I assumed it was permitted development” is not a defence.

Building regulations: yes, and this is the one people miss

Part H of the Building Regulations covers drainage and waste disposal, and it applies to a new or replacement septic system regardless of whether planning permission was needed.

That means Building Control notification and sign-off. It covers how the system is installed — siting, depth, distances from buildings and boundaries, the drainage field design and construction.

This is the approval most often skipped, usually because the homeowner reasonably concluded that “no planning permission needed” meant “no approval needed”. It does not.

It also matters later. When you sell, a buyer’s solicitor may ask for the Building Control completion certificate for a system installed during your ownership. Not having it is the kind of thing that produces an indemnity policy and an awkward conversation — see buying or selling a house with a septic tank.

Environment Agency: a different regime entirely

The Environment Agency does not care whether you had planning permission. It governs the discharge.

Under the General Binding Rules, a domestic discharge is allowed without a permit provided it meets the conditions — including that a septic tank discharges to a drainage field and not directly to a watercourse, and that volumes stay within the thresholds.

Where those conditions are not met — a large discharge, a Source Protection Zone, a discharge to surface water — you need a permit instead. See do I need to register my septic tank?.

You can have full planning permission, full building regulations sign-off, and still be in breach here. They are independent.

How they interact in practice

For a typical Cornwall replacement on an existing house:

Regime	Usually needed?	Who
Planning permission	No — permitted development	Cornwall Council (check if listed/designated)
Building regulations	Yes	Building Control
Environment Agency	General Binding Rules apply; permit only if they are not met	Environment Agency

The sequence that works: establish the discharge position first (it determines what system is viable), then the percolation test (it determines the drainage field), then Building Control — and planning only if a designation or an above-ground structure brings it in.

Where this most often goes wrong

• A system installed years ago with no Building Control record, discovered at sale.
• An annexe or holiday let added to an existing system without anyone checking the tank’s capacity — which is both a building regulations and a General Binding Rules problem.
• A replacement that quietly changes where the discharge goes, without rechecking the Environment Agency position.

The short version

• Planning: usually not needed for a below-ground tank at an existing house — but check if listed or in a designated area.
• Building regulations: yes, always. Part H, via Building Control. This is the commonly missed one.
• Environment Agency: separate again. General Binding Rules, or a permit.
• Satisfying one regime says nothing about the others.

Start with where your discharge stands — the free compliance checker covers that in a couple of minutes.

Sources: Planning Portal — planning permission · GOV.UK — Approved Document H: drainage and waste disposal · GOV.UK — Permits you need for septic tanks