Where Should a Downpipe Drain?

A roof collects a lot of water in a short time, and every drop reaches the ground through a downpipe. If the bottom of that pipe empties onto a path or a flower bed beside the wall, the water soaks the ground against your foundations, splashes the brickwork and, in a hard downpour, can run back towards the house. That is why the place where a downpipe ends is as important as the gutter above it.

The usual answer is a rainwater gully. This is a small trapped inlet at ground level, often a grey or brown grate with a square or round hopper, that connects to an underground drain. The downpipe sits over it or is bent in at the foot, so the water goes straight below ground.

Look at where your downpipes finish. A pipe that stops short of the grate, a broken shoe at the bottom or a gully clogged with leaves will each send water the wrong way. If the water is going somewhere you cannot see, a drain survey may be needed to find out, which falls to a drainage firm, not a roofer. Our answer on a blocked downpipe covers clearing the pipe itself.

There are three common destinations for roof water, and a house may use more than one.

Into a drain through a gully

On most streets built up as estates, rainwater goes to a drain beneath the property. Some drains take only rain and carry it away separately; others are combined with the foul sewer. Your water company can tell you which applies to your address.

Into a soakaway

A soakaway is a buried pit, filled with rubble or fitted with a crate system, that lets the water seep into the ground. It only works where the soil drains freely and the site is well away from buildings. Clay soil, which holds water, can make a soakaway fail slowly, so it needs proper design rather than guesswork.

Into a water butt

A water butt collects rain for the garden. It must have an overflow connected back to the drain or soakaway, because a butt fills fast and a full one with no outlet sends the water straight back onto the ground. A diverter kit fitted to the downpipe does this neatly.

Whichever you choose, the water should flow away from the house, not towards the doors or the neighbour's boundary.

Rainwater drainage is covered by the Building Regulations in England, which is why a new or altered drain is normally something to raise with your building control body before any digging starts. We do not give legal advice and this is not a list of the rules; it is a pointer to the right person. In Crawley the local authority service is Crawley Building Control, elsewhere it is your own council's team, and anywhere a registered building control approver can act.

Simple like-for-like work, such as replacing a cracked shoe or fitting a new section of pipe onto an existing gully, is the sort of repair that usually leaves the drainage unchanged. Changing where a downpipe discharges, building a new soakaway, or connecting to a sewer is different, and it can need approval or the water company's consent. Ask before you start.

Guttering also has to be sized for the rain that lands on the roof, and BS EN 12056-3 is the standard behind the layout and sizing of roof drainage. On an ordinary house the roofer matches pipe and gutter to the roof area.

If you are unsure, a call to building control costs nothing and saves a wasted job.

Water pooling at the foot of a downpipe has a short list of causes. The gully may be blocked with silt or moss. The pipe may have come loose from its shoe and be spilling above the grate. A cracked underground run can leak, and then the gully fills and overflows. Or the soakaway may be saturated, so it is full before the storm has finished.

Start with what you can see. Pour a bucket of water down the downpipe in dry weather and watch where it goes. If it backs up in the pipe, the blockage is above ground. If it appears at the base or drains slowly, the trouble lies in the gully or the pipe run underneath.

The roofer's part is the pipe, the brackets and the shoe, and we also look at whether the pipe is connected squarely to the gutter outlet. Anything below ground belongs to a drainage specialist. When your gutters overflow in heavy rain and the downpipe is clear, our answer on why gutters overflow goes through the other causes, and the gutters, soffits and fascias page sets out the wider work. Email a photo of the base of the downpipe and the nearest gully, and we will name the first thing we would check.