A rain gutter, eavestrough, eaves-shoot or surface water collection channel is a component of a water discharge system for a building. It is necessary to prevent water dripping or flowing off roofs in an uncontrolled manner for several reasons: to prevent it damaging the walls, drenching persons standing below or entering the building, and to direct the water to a suitable disposal site where it will not damage the foundations of the building. In the case of a flat roof, removal of water is essential to prevent water ingress and to prevent a build-up of excessive weight. Water from a pitched roof flows down into a valley gutter, a parapet gutter or an eaves gutter. An eaves gutter is also known as an eavestrough (especially in Canada), spouting (in New Zealand), rhone or rone (Scotland), eaves-shoot (Ireland), eaves channel, dripster, guttering, rainspouting or simply as a gutter. The word gutter derives from Latin gutta (noun), meaning "a droplet". Guttering in its earliest form consisted of lined wooden or stone troughs. Lead was a popular liner and is still used in pitched valley gutters. Many materials have been used to make guttering: cast iron, asbestos cement, UPVC (PVCu), cast and extruded aluminium, galvanized steel, wood, copper, zinc, and bamboo.
Description Gutters prevent water ingress into the fabric of the building by channelling the rainwater away from the exterior of the walls and their foundations. Water running down the walls causes dampness in the affected rooms and provides a favourable environment for growth of mould, and wet rot in timber. A rain gutter may be a:
Roof integral trough along the lower edge of the roof slope which is fashioned from the roof covering and flashing materials. Discrete trough of metal, or other material that is suspended beyond the roof edge and below the projected slope of the roof. Wall integral structure beneath the roof edge, traditionally constructed of masonry, fashioned as the crowning element of a wall. A roof must be designed with a suitable fall to allow the rainwater to discharge. The water drains into a gutter that is fed into a downpipe. A flat roof should have a watertight surface with a minimum finished fall of 1 in 80. They can drain internally or to an eaves gutter, which has a minimum 1 in 360 fall towards the downpipe. The pitch of a pitched roof is determined by the construction material of the covering. For slate this will be at 25%, for machine made tiles it will be 35%. Water falls towards a parapet gutter, a valley gutter or an eaves gutter. When two pitched roofs meet at an angle, they also form a pitched valley gutter: the join is sealed with valley flashing. Parapet gutters and valley gutters discharge into internal rainwater pipes or directly into external down pipes at the end of the run.
The capacity of the gutter is a significant design consideration. The area of the roof is calculated (metres) and this is multiplied by rainfall (litres/sec/metres²) which is assumed to be 0.0208. This gives a required discharge outfall capacity. (litres/sec) . Rainfall intensity, the amount of water likely to generated in a two-minute rainstorm is more important than average rainfall, the British Standards Institute notes that an indicative storm in Essex, (annual rainfall 500 mm per annum) delivers 0.022 L/s/m²- while one in Cumbria (annual rainfall 1800 mm per annum) delivers 0.014 L/s/m². Eaves gutters can be made from a variety of materials such as cast iron, lead, zinc, galvanised steel, painted steel, copper, painted aluminium, PVC (and other plastics) and occasionally from concrete, stone, and wood.
Water collected by a rain gutter is fed, usually via a downpipe (also called a leader or conductor), from the roof edge to the base of the building where it is either discharged or collected. The down pipe can terminate in a shoe and discharge directly onto the surface, but using modern construction techniques would be connected through an inspection chamber to a drain that led to a surface water drain or soakaway. Alternatively it would connect via a storm drain (u-bend) with 50 mm water seal to a combined drain. Water from rain gutters may be harvested in a rain barrel or a cistern. Rain gutters can be equipped with gutter screens, micro mesh screens, louvers or solid hoods to allow water from the roof to flow through, while reducing passage of roof debris into the gutter. Clogged gutters can also cause water ingress into the building as the water backs up. Clogged gutters can also lead to stagnant water build up which in some climates allows mosquitoes to breed.
History The Romans brought rainwater systems to Britain. The technology was subsequently lost, but was re-introduced by the Normans. The White Tower, at the Tower of London had external gutters. In March 1240 the Keeper of the Works at the Tower of London was ordered by King Henry "to have the Great Tower whitened both inside and out". This was according to the fashion at the time. Later that year the king wrote to the Keeper, commanding that the White Tower's lead guttering should be extended with the effect that "the wall of the tower ... newly whitened, may be in no danger of perishing or falling outwards through the trickling of the rain". In Saxon times, the thanes erected buildings with large overhanging roofs to throw the water clear of the walls in the same way that occurs in thatched cottages. The cathedral builder used lead parapet gutters, with elaborate gargoyles for the same purpose. With the dissolution of the monasteries- those buildings were recycled and there was plenty of lead that could be used for secular building. The yeoman would use wooden gutters or lead lined wooden gutters.
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