Rainwater Systems: Gutters, Downpipes and Drainage

A practical guide to gutter and downpipe sizing, materials, fall and fixing, and where water should go once it leaves the pipe.

A rainwater system is one of the least noticed parts of a house and one of the hardest working. If water running off the roof is not guided away, it soaks the facade, washes out the plinth and pools around the foundations. Gutters and downpipes collect that water and take it to a controlled point, so choosing them properly matters as much as the roof itself.

What the system consists of

A typical system includes gutters along the eaves, brackets holding them, an outlet that passes water down, vertical downpipes, offset bends and a shoe or outlet at the bottom. Corners need angle pieces and gutter ends need stop ends. Every joint is a potential leak, so assembling the system from compatible components by one manufacturer makes installation easier.

How sizing works

The gutter width and the number of downpipes depend on the roof area draining to that side. What counts is not the floor area of the house but the plan area of the roof slope. Manufacturers’ catalogues state how much roof area one downpipe can serve for each gutter size.

On a long slope a single downpipe is not enough, and the flow has to be split in two directions. Where heavy downpours are common, an undersized gutter will overflow. The usual approach is to go one size up or add more downpipes.

Choosing a material

The most common options are:

• PVC — light, rust-free and simple to install; it expands and contracts with temperature, so it needs expansion joints.
• Galvanised steel with a polymer coating — strong and easy to match to the roof colour; scratches in the coating should be touched up promptly.
• Aluminium — light and corrosion-resistant, often roll-formed seamlessly on site.
• Copper and zinc-titanium — long-lasting and decorative, often chosen for classic facades, but they must not be in contact with other metals.

Compatibility with the roof covering matters too: direct contact between different metals can cause galvanic corrosion.

Key installation rules

A gutter is not fitted dead level but with a slight fall towards the outlet so water does not stand in it. Brackets are spaced evenly; if they are too far apart the gutter sags under snow and ice. The outer edge of the gutter is positioned relative to the roof edge so that water and snow sliding off the slope do not tear it away.

Downpipes are fixed to the facade with purpose-made clips and held slightly off the wall so moisture does not collect behind them. Each joint must follow the direction of flow: the upper section sits inside the lower one.

Where the water goes after the downpipe

This is the most overlooked part of the system. If the pipe simply dumps water at the base of the plinth, the problem just moves lower. There are several ways to take water away from the house:

• fit an outlet bend that discharges clear of the foundations, with a concrete or stone splash block beneath;
• connect the downpipe to an underground surface-water drain or soakaway;
• collect the water in a tank for watering the garden.

For underground connections, the gully should have a debris basket; otherwise leaves form blockages inside the pipe.

Connecting rainwater to the foul sewer is generally not considered good practice. The large volume arriving in a downpour can surcharge the sewer and back up, and in many places it is not permitted anyway. If the plan is to let water soak into the ground, the soakaway should sit well clear of the foundations, and the soil’s ability to drain should be checked first. Clay soils absorb water slowly and a soakaway can overflow; in that case it has to be considered together with the overall drainage layout of the plot. Discharging onto a neighbour’s land or the pavement also leads to disputes, so the end point of the flow should be clearly shown in the design.

Maintenance and a checklist

Gutters should be cleaned at least twice a year, especially in autumn after leaf fall. Walking around the house during a heavy shower is the best test:

• does water spill over the gutter edge;
• are any joints dripping;
• does water splash against the wall at the downpipe outlet;
• is there standing water near the plinth?

If you see any of these, the cause is usually a blockage, a lost fall or a system that is too small.

Zaferoğlu İnşaat builds the roof covering and its related details to the project when constructing private houses. Ask us to mark gutters and downpipes on the roof plan together with where the water will be led across the yard.