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Building components · Drainage Elements

Downpipe

Explains the downpipe as a conveyance whose discharge point matters as much as the pipe itself.

Form:Conveyance elementRoles:Drainage

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 downpipe is

A downpipe takes water from a gutter or roof outlet and carries it down the face of the building to where it discharges — a gully, a drain connection, or a surface at ground level.

Where it discharges is as consequential as the pipe. A downpipe delivering a whole roof's water to the ground beside a wall is concentrating that water exactly where it does most harm, which is why the connection at its base is part of the element rather than an afterthought.

Boundaries

How it differs from nearby elements

The distinctions that keep this entry from being a restatement of its neighbours.

  • It is not a gutter. Gutters collect along a roof edge; downpipes carry vertically.
  • It is not a soil or waste pipe. Those carry foul drainage and are separate systems, though both are vertical pipes on a building.
  • It is not a gully. The gully is what commonly receives the downpipe's discharge.

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.

  • downpipes
  • rainwater pipe
  • downspout
  • leader

Dependencies

What it depends on

What has to be right elsewhere for this element to do its job.

  • Where it discharges, and whether that discharge is connected or simply released at the surface.
  • Its capacity relative to the outlet feeding it and the roof area behind that.
  • Its fixings, since a full downpipe is heavy and the fixings are into the wall face.
  • Being clear, since blockages in a vertical pipe cause the gutter above to overflow.

Considerations

Topics that genuinely apply here

Subjects worth discussing about this element. These are discussion topics, never measured values, ratings or performance claims.

Moisture

A downpipe discharging at the base of a wall concentrates a roof's worth of water there, and that is a common cause of damp and of ground movement near foundations.

Maintenance & access

Blockages within a downpipe are hard to locate and clear, particularly where the pipe is enclosed or built in.

Durability

Leaking joints wet a vertical strip of wall continuously, which shows as staining and localised deterioration.

Buildability

Downpipes built into or concealed within construction are far more difficult to maintain than surface-fixed ones.

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.

Materials LibraryPVC Foam Board →PVC-U downpipes are the most widely encountered domestic form.Materials LibraryAluminium →Aluminium downpipes are used where appearance and durability govern.Materials LibraryZinc sheet →Zinc downpipes are met alongside zinc gutters in traditional work.Materials LibraryCopper sheet →Copper is used where longevity and appearance are both wanted.Materials LibraryGalvanised steel →Coated steel pipes are met in commercial and industrial buildings.

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.

Drainage planeRoof Rainwater Drainage →Carries collected water from the outlet down to the discharge point.Drainage planeSiphonic Roof Drainage →Runs full bore rather than by gravity, which changes how the pipework is arranged.Drainage planeRainwater Harvesting →Conveys collected water toward the storage rather than to a drain.Drainage planeSurface Water Collection →Delivers roof water into the surface water system at ground level.

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.

  • Site Drainage

Related elements

Neighbouring components

Typed relationships to other elements. There is deliberately no generic “related” category: an edge that cannot be classified does not exist.

Clarifications

Commonly misunderstood

  • That where a downpipe discharges is a landscaping matter. It determines whether a roof's water is taken away or delivered to the foundations.
  • That a downpipe blockage shows at the downpipe. It generally shows as the gutter above overflowing.

Conversations

Questions for qualified professionals

Questions worth asking someone with the project in front of them. This page cannot answer them.

  • Where does this downpipe discharge, and is that connected to a drainage system?
  • Is the pipe's capacity matched to the roof area and outlet feeding it?
  • Is the downpipe accessible for clearing along its length?
  • Is there evidence of leaking joints staining the wall behind it?

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 diameter, capacity, fixing or discharge arrangement is stated here.
  • Rainwater drainage design and connection to below-ground drainage are regulated and 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 →