Cast Iron Downpipes

Buying a replacement pipe sounds simple until you start looking at the options. Diameter, length, profile, fixing style and finish all matter - and older buildings don't always use exactly the same arrangement as the house next door.

The easiest starting point is to identify what is already on the property. If you're installing a completely new system, work backwards from the gutter outlet and the amount of rainwater the roof needs to handle.

Round Cast Iron Downpipes

Round cast iron rainwater pipes are the traditional choice for everything from Victorian terraces and cottages to churches, schools and larger heritage properties.

They work particularly well alongside cast iron guttering, and you can choose from several pipe lengths rather than cutting every section down on site.

Our 2.5" range includes 2ft, 3ft, 4ft and 6ft lengths, with eared and uneared versions available. If your existing system is larger, browse our dedicated 3 inch cast iron downpipes or the wider Hargreaves round cast iron range.

Rectangular Cast Iron Downpipes

Straight-sided pipes aren't simply a modern alternative. Rectangular cast iron has a long history of use on traditional and heritage buildings too, and is often the correct choice when matching an existing rainwater system.

Our dedicated rectangular iron downpipes use a 4 × 3" profile, approximately 100 × 75mm, with matching bends, offsets, shoes, branches and fixings.

If you're replacing an old rectangular pipe, measure both sides of the pipe body rather than assuming it is a standard square section.

2.5", 3" Or 4" Cast Iron Downpipe?

Cast iron pipe sizes are still commonly described in inches, which is often more useful when you're working on an older property.

A 65mm cast iron downpipe is normally referred to as 2.5". It's a familiar size on smaller and traditional domestic rainwater systems and is the size you'll see most heavily represented in the products above.

The next common step is the 75mm cast iron downpipe, usually called 3". Larger systems may use a 100mm cast iron downpipe, or 4".

Don't choose the pipe diameter in isolation, though. It needs to suit the gutter outlet and the drainage requirements of the roof. Changing to a bigger gutter while leaving a small outlet and pipe beneath it can simply move the restriction further down the system.

If you're planning a full replacement rather than swapping a single damaged section, send your roof dimensions or drawings to the Trade Warehouse team and we can help you work through the main components.

Eared Or Uneared?

This catches plenty of people out. An eared cast iron downpipe has fixing lugs incorporated into the socket. These provide a traditional fixing point and are particularly useful where you want the pipe itself secured back to the wall. An uneared cast iron downpipe has a cleaner plain socket without those projecting fixing ears. Separate earbelts or pipe brackets are then used to support the stack.

Neither version is inherently better. If you're replacing part of an existing installation, matching the fixing style already on the building usually gives the neatest result. Take a photograph of the socket if you're unsure. The difference is much easier to identify from a picture than from a written description.

Painted Black Or Primed Cast Iron?

This decision is mostly about how you want to finish the job.

Pre-Painted Black

A black cast iron downpipe is a straightforward choice when you want the familiar traditional finish without applying the main decorative coating on site.

It works particularly well against red brick, stonework and period façades, and means the visible rainwater system already arrives in the classic colour most people associate with cast iron.

Always touch up any areas damaged during cutting or installation using the appropriate compatible coating.

Primed

A primed cast iron downpipe gives you more freedom over the final appearance.

The primer is a preparation coat rather than the finished decorative surface, so the pipe still needs the appropriate topcoat after installation. This is useful when matching existing heritage paintwork or specifying a particular colour across the building.

If colour matching is important, confirm the required finish before ordering rather than relying on how a shade appears on a screen.

Bends, Offsets And Fixings Explained

A straight vertical wall is the easy part. Roof overhangs, cornices, plinths and architectural details are where the fittings become important.

When Do You Need A Bend?

Bends change the direction of the pipe and are commonly used near the top of the stack to bring the pipe from the gutter outlet back towards the wall.

Different angles are available, including 112.5° and 135° fittings across the current 2.5" range.

The correct angle depends on the layout of the outlet and the position you want the vertical pipe to follow.

What Is A Cast Iron Downpipe Offset?

An offset moves the pipe around an obstruction or bridges the horizontal distance between two vertical sections.

This is especially common on period properties where decorative brickwork, projecting eaves or stone details prevent a simple straight drop.

Our current 2.5" range includes offsets in a wide choice of projections, so don't guess. Measure the horizontal distance you actually need to clear and choose the closest appropriate fitting.

For unusual architecture, custom angles and lengths may also be available on request.

Brackets, Earbelt Fixings And Loose Sockets

The rest of the cast iron downpipe fittings matter just as much as the pipe.

Separate pipe brackets can support uneared sections, while earbelts provide a more traditional fixing detail. Loose sockets are particularly useful where a cut pipe or offcut needs turning back into a usable socketed section rather than being wasted.

At the bottom of the run you'll normally finish with a shoe, anti-splash shoe or suitable connection into the drainage system.

Build The Complete Cast Iron Rainwater System

A downpipe rarely sits on its own.

From the roof down, a complete system might involve cast iron gutters, an outlet, a bend or offset, the vertical pipes and supports, then a shoe or drainage connection at ground level.

Where water from several roof areas needs to meet before entering the pipe, a cast iron hopper can provide a much neater transition. Our hopper range includes 2.5", 3" and 4" round outlets as well as rectangular options, so the hopper can be matched to the pipe below.

Try to keep components within the same compatible system. Old cast iron installations and products from different manufacturers can look extremely similar while still differing slightly at sockets, fittings and dimensions.

Replacing An Existing Cast Iron Pipe?

This is where a few measurements can save a lot of hassle. Before ordering, take a clear photo of the entire downpipe and a closer image of the socket and fixing arrangement. Then measure the outside diameter of the pipe body rather than the enlarged socket, along with the overall length of the section you're replacing.

Also note whether the socket has fixing ears and whether there is an offset at the top.

If it's rectangular, measure both dimensions.

With those details, we can usually narrow the system down much more quickly than working from a description such as “old black drainpipe”.

Why Buy Cast Iron Downpipes From Trade Warehouse?

We don't just stock straight lengths. Trade Warehouse supplies the bends, offsets, brackets, sockets and matching rainwater goods needed to put together a proper system, whether you're repairing one damaged section or replacing an entire elevation.

Pre-painted black and primed options are available, with fast UK delivery across the core ranges. For less straightforward jobs, send us your existing measurements, photographs or drawings before ordering.

That way, you can sort the profile, pipe size and fittings first — rather than discovering the wrong socket or offset once the cast iron is already on site.