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.
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.
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
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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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