- Project plans
- Project activities
- Legislation and standards
- Industry context
Last edited 03 Jan 2018
A rainwater downpipe is a pipe that is used to direct rainwater away from a building, typically from roof guttering to a drainage system. It is sometimes also referred to as a downspout, drain spout, roof drain pipe or leader.
The Building Regulation’s part H, Drainage and water disposal, requires that adequate provision is made for rainwater to be carried from the roof of buildings. Approved document H suggests that to achieve this, roofs should be designed with a suitable fall towards either a surface water collection channel or gutter that surface water to vertical rainwater downpipes, which in turn connect the discharge to the drainage system.
A downpipe is typically vertical and extends to ground level. They are most commonly found attached to the corners of a building. The discharge from a downpipe can be:
- Directly connected to a drain discharging into a soakaway.
- Directly connected to a drain discharging into a surface water sewer.
- Indirectly connected to a drain via a trapped gully if the drain discharges into a combined sewer.
Traditionally, rainwater downpipes were made using cast iron, although uPVC systems are increasingly common due to ease of installation and low maintenance requirements. As long as adequate size, strength and durability can be assured, they can also be made of aluminium alloy, galvanised steel, stainless steel, and so on.
Downpipes have a tendency to become blocked when debris such as leaves and twigs accumulate. To prevent this, they should be properly maintained, and are usually attached to a building using brackets which can be easily removed for cleaning if necessary.
The size and number of rainwater downpipes required will depend on the intensity of rainfall that is likely and the area of the surface to be drained. A number of online calculators are available to help determine the required size and number of rainwater downpipes.
Rainwater downpipes are most commonly round in section, but may be any shape. They typically have a diameter ranging from 50 - 150 mm, but any size can be used. They may include access panels for inspection or rodding, branch connectors, bends, hoppers and leaf guards at the top, diverters, rainwater harvesting systems, angled shoes at the bottom, and so on.
 Related articles on Designing Buildings Wiki
Featured articles and news
Which room is the most fun to design? Find out the 'Grand Designs' presenter's unusual choice in our interview.
Full suite of speakers are announced for this year's BSRIA Briefing event.
Book your place for the Architectural Technology Awards 2018.
There are many ways of classifying types of building. Have a look at our range of building articles.
BSRIA have launched the 'major update' of the go-to design framework guide for building services.
How to get results with building life cycle assessment.
Government publishes a prospectus inviting proposals for new 'garden communities'.
The Morandi motorway bridge in Genoa collapses during rainstorm while undergoing maintenance works.
'Developed design' is a phrase coined by the RIBA for their 2013 Plan of Work. But what does it actually mean?
New green paper published aiming to rebalance the relationship between landlords and residents and tackle stigma.
RIBA calls for a comprehensive ban on combustible materials.