Buildings Without Rainwater Goods
Some buildings have traditional pitched roofs with deep projecting eaves that allow water to run off and be thrown well away from the property, without the need for downpipes or gutters. Also, some roofs with parapet gutters only have spouts to throw rainwater clear of the walls.
To ensure rain backsplash does not occur at the base of a property, it is important that the surrounding ground is sloping away from the building and does not provide a hard surface to enable water to bounce back. Softer landscaping or gravel will absorb water and prevent splashback and water pooling at the foot of walls. In some circumstances, it may be feasible and beneficial to improve the perimeter drainage.
Perimeter land drains and open drains
Perimeter land drains are perforated pipes laid in below ground trenches which can be installed next to buildings without rainwater goods to catch rainwater and surface water. They should be protected from silting up (for example, by incorporating a catchpit) and designed with accessible rodding points to allow for maintenance. The trench should be backfilled with a compacted layer of earth, preferably with a high clay content. This type of backfill resists water penetrating from above but allows capillary rise of water from below, which will dry through evaporation.
Perimeter land drains encased in gravel, commonly known as French drains, are suited to agricultural use. However, when installed near building foundations, they may concentrate water at the base of the walls. This may increase the risk of water penetration or undermine the stability of shallow foundations.
Open drains may be more suitable if moisture needs to evaporate from the bottom of walls, for example where ground levels have risen around a building. If designed with care and consideration, open drains may, in certain circumstances, be used to redirect surface and subsoil water away from foundations or to disperse liquid moisture in a clay soil that is not free draining.
Thatched buildings
Many thatched buildings don’t have gutters. Instead, the wide eaves of the roof throw rainwater clear of the walls and it is collected at ground level and directed into the drains. However, to avoid water dripping on people, gutters might be needed above a doorway or where a path runs alongside a building.
Where gutters are installed, they need to be able to accommodate a receding drip line as the thatch wears over time. One traditional option is to use tar-lined V-shaped timber gutters which have a wider mouth than conventional cast iron gutters. Alternatively, cast iron gutters can be fixed on steel brackets with an adjustable support that allows them to be realigned as the thatch recedes. Gutters on thatched roofs must be inspected frequently as they can quickly become clogged with debris from the roof.
