Defra FDA1 • Septic Tanks & Package Treatment • General Binding Rules

Foul Drainage Assessment FDA1 for Non-Mains Drainage

No mains sewer to connect to? We prepare the Foul Drainage Assessment (FDA1) that planning needs — justifying the drainage hierarchy and specifying a compliant septic tank or package treatment plant under the General Binding Rules — plus full foul drainage design where a scheme requires it.

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Defra FDA1 form
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Drainage hierarchy justified
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Septic & package treatment
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General Binding Rules
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Percolation testing

Foul Drainage Assessments for Planning

Where a development cannot connect to the public foul sewer, the LPA will usually require a Foul Drainage Assessment on the Government’s standard FDA1 form. It demonstrates that the proposed means of foul disposal has been chosen correctly against the drainage hierarchy — mains connection first, then a package treatment plant, and only then a septic tank — and that the discharge will comply with the Environment Agency’s General Binding Rules or, where needed, a permit.

We complete the FDA1, justify the chosen solution, specify a suitable septic tank or package treatment plant, and where discharge is to ground we arrange the percolation testing needed to size the drainage field to Building Regulations Part H and BS 6297. The result is a submission-ready assessment that satisfies both planning and Building Control.

What’s Included

  • ✓ FDA1 form completed — the Defra Foul Drainage Assessment form filled in and justified
  • ✓ Drainage hierarchy evidenced — mains connection properly investigated and discounted before off-mains options
  • ✓ System specification — package treatment plant or septic tank sized for the development
  • ✓ Percolation / porosity testing — arranged where discharge is to a drainage field, to size it correctly
  • ✓ General Binding Rules check — confirmation the discharge complies, or identification of where an EA permit is required
  • ✓ Watercourse discharge — treatment and consenting requirements where discharge is to a watercourse rather than ground

Foul Drainage Design

Beyond the FDA1, many sites need the foul system fully designed — to connect to the public sewer, discharge a planning condition, or build from.

Sewer connection & capacity

Where a public foul or combined sewer is available, we establish the connection point, available capacity and the agreement needed to connect.

Detailed network design

Foul network layout, pipe sizing, gradients and falls, with full calculations to support technical approval and construction.

Pumped systems

Foul pumping station and rising main design where a site can’t drain to sewer by gravity.

Condition discharge

Discharging pre-commencement or pre-occupation foul drainage conditions, co-ordinated with surface water where required.

Discharging a foul drainage condition? Send your decision notice and the condition wording and we’ll confirm what the design needs to demonstrate. Foul design is often co-ordinated with surface water under a SuDS drainage strategy and detailed drainage design.

Foul drainage pipework Drainage and sewer pipes Rural property off the mains sewer

When Do You Need a Foul Drainage Assessment?

Rural site with no mains drainage? Tell us the location and we’ll advise.

No Mains Sewer Available

Where the nearest public foul sewer is too far or too costly to connect to, an FDA1 justifies an off-mains solution.

Conditioned Foul Drainage

Conditions requiring foul drainage details to be approved before commencement or occupation — we discharge these too.

New Rural Dwellings

New homes in the countryside almost always rely on a package treatment plant or septic tank, which the FDA1 must support.

Conversions & Barn Developments

Change of use and barn conversions frequently need a fresh foul drainage assessment even where one existed before.

Replacing a Failing System

Upgrading an old septic tank to a compliant package treatment plant, including bringing discharges within the General Binding Rules.

Discharge to Ground or Watercourse

Either route has specific compliance requirements; we identify whether the General Binding Rules suffice or an EA permit is needed.

Frequently Asked Questions

What is the FDA1 form?
FDA1 is the Government’s standard Foul Drainage Assessment form. It records the proposed method of foul drainage and the justification for it against the drainage hierarchy, and is the document LPAs expect for off-mains schemes.
Septic tank or package treatment plant?
Septic tanks sit below package treatment plants in the hierarchy and are only acceptable where a treatment plant isn’t reasonable. Most new schemes now use a package treatment plant, which produces a cleaner effluent and is easier to consent.
Do you design the full foul drainage system, not just the FDA1?
Yes. Alongside the FDA1 we provide detailed foul drainage design — connection to the public sewer, network layout and pipe sizing, foul pumping stations and rising mains where gravity won’t reach, and off-mains package treatment. See detailed drainage design →
Do I need an Environment Agency permit?
Many small domestic discharges are covered by the EA’s General Binding Rules and don’t need a permit, provided the rules are met. Larger or more sensitive discharges do. We tell you which applies and arrange a permit if needed.
What is a percolation test?
Where treated effluent discharges to a drainage field, a percolation (porosity) test measures how quickly the soil absorbs water, so the drainage field can be sized correctly to Building Regulations Part H. We arrange and interpret it.
How much does it cost?
A fixed fee depending on whether percolation testing and permit support are required. We’ll quote within 24 hours of seeing your site.

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Free, no-obligation fixed-fee quote within 24 hours. Off-mains foul drainage assessments and full foul drainage design, across England and Wales.

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