Building components · Drainage Elements
Channel Drain
Explains linear interception as a different mechanism from point drainage, and where that difference matters.
Educational reference entry. What this element has to do, and whether any particular arrangement of it is adequate, depends on the whole assembly, the loading, the exposure, local requirements, the manufacturer's instructions and qualified professional design.
Overview
What a channel drain is
A channel drain runs as a line across a surface, intercepting water flowing over it. Unlike a gully, which needs water to be directed toward one point, a channel catches everything crossing its length.
That makes it the usual answer where water must be stopped from reaching something: across a driveway before a garage, or immediately outside a level threshold where there is no step to keep water out.
Boundaries
How it differs from nearby elements
The distinctions that keep this entry from being a restatement of its neighbours.
- It is not a gully. A gully collects at a point and needs falls directing water to it; a channel intercepts along a line.
- It is not a gutter. A gutter is at a roof edge; a channel is set into a trafficked surface.
- It is not a French drain or land drain. Those collect water from within the ground; a channel intercepts surface flow.
Terminology
Common names and aliases
These names describe the same element. The library keeps one entry per component so that a trade term or a regional name never becomes a second, thinner page.
- linear drain
- slot drain
- ACO channel
- threshold drain
Dependencies
What it depends on
What has to be right elsewhere for this element to do its job.
- Being at or below the level of the surface draining into it, since a channel proud of the surface is bypassed.
- Its outlet, since the channel collects but must discharge somewhere.
- Its ability to carry traffic, where it crosses a driveway or a loading area.
- Being accessible for clearing, since a linear channel collects debris along its whole length.
Considerations
Topics that genuinely apply here
Subjects worth discussing about this element. These are discussion topics, never measured values, ratings or performance claims.
Linear interception catches sheet flow across a surface, which point drainage can only do if the surface falls precisely toward it.
At a level threshold, the channel immediately outside is commonly the only thing preventing water entering the building.
A channel crossing a driveway is loaded by every vehicle, and both the channel and its surround have to be built for that.
Channels silt along their length, and a grating that cannot be lifted means they are never cleared.
Materials
Commonly formed from
Material families this element is commonly realised in. This states common practice only — it is not a statement that any of these materials suits this component in a particular building, which depends on the whole assembly and on qualified review.
Assemblies
Building systems this element is met in
The role this component fills inside each assembly. A role describes what the element does there — it is not a statement that this component suits that system in any particular building.
Junctions
Interfaces this element takes part in
Junctions where the condition between this element and another governs how the construction behaves. These name the junction and the subjects it raises; they are not details, arrangements or approved ways of building.
Threshold to External Ground
Where a door opening meets the ground outside, and where keeping water out and letting people in are in direct conflict.
Raises: Moisture · Drainage · Thermal continuity · Buildability
Where it is met
Application contexts
Building contexts where this element is commonly encountered. Association is not recommendation: appearing here does not mean the component suits every instance of that context, or any particular one.
- Hardstanding
- Site Drainage
Clarifications
Commonly misunderstood
- That a channel drain and a gully are interchangeable. They intercept water by different mechanisms and suit different situations.
- That a channel outside a level threshold is a refinement. It is commonly what makes level access viable at all.
Conversations
Questions for qualified professionals
Questions worth asking someone with the project in front of them. This page cannot answer them.
- Is the channel set at or below the surface draining into it?
- Where does the channel discharge, and does that route have capacity?
- What loading will cross the channel, and are the channel and its surround built for it?
- How is the channel cleared, and can the grating be lifted?
Go deeper
Related Build Design Hub guides
Planning guidance behind the decisions this element involves.
Preparation
Related planning checklists
Owner-side preparation before the conversation where this element comes up.
What this entry does not do
- No size, capacity, loading class or outlet arrangement is stated here.
- Surface water drainage design and load classification of drainage components are professional matters.
Drainage & Rainwater Elements
The gutters, outlets, downpipes, channels, chambers and traps that collect water, carry it and let it be inspected.
Browse all drainage elements entries →