French Drain vs ACO Drain — What’s the Difference (and When to Use Each)?

When clients ask, “French drain or ACO drain—aren’t they the same thing?”, the simple answer is: they solve the same problem (moving rainwater away safely), but they do it in different ways and are used in different places. In many projects we actually use both together.

The quick verdict

• Both manage rainwater and protect buildings from flooding and damp.
• ACO / linear channel drains collect surface water at finished level (door thresholds, patios, driveways).
• French drains collect and attenuate subsurface water using a perforated pipe in free-draining gravel—great for soggy lawns, garden edges, and along retaining walls.
• Best practice on residential schemes: channel drain at the threshold → piped to a soakaway or SuDS system(often a short run of French drain or a modular crate soakaway).

Can I use both?

Yes—and that’s common. A typical detail at a patio door: ACO linear channel at the threshold → pipe drop → soakaway / SuDS feature. In gardens with persistent saturation: French drain along the wet edge → connect to the same soakaway.

Rules, approvals, and SuDS context (London/UK)

• New or refurbished drainage should comply with SuDS principles (manage water on site, slow the flow).
• Discharge to combined or surface water sewers may need approval from your water company; many boroughs prefer infiltration first (soakaway) where ground allows.
• Works on or affecting the public highway may require Section 278/50 approvals and reinstatement to highway standards.

Authoritative London/UK resources to link in your post

• CIRIA SuDS Manual (C753) – UK’s primary SuDS best-practice reference.
• Greater London Authority – London Sustainable Drainage Guidance / Action Plan – policy context and design direction for London.
• Thames Water – Surface water connections & Build-over guidance – approvals and what’s allowed near public sewers.
• Gov.uk – Rainwater harvesting and permeable paving guidance – overarching planning and drainage principles.