Rainwater Disposal: Gutters and Downpipes

The rainwater collection and disposal system consists of gutters and downspouts. Without the presence of such a system, the rain would wash away freely along the perimeter walls of a building, dragging dirt and aggressive chemical agents with it which could cause deterioration of the walls and the formation of spots and streaks with consequent aesthetic damage.

However, beyond the external deterioration, the rainwater could also penetrate inside the wall structure, causing infiltrations and, in the long run, structural damage. To pursue this aim it is important that gutters and downspouts are not damaged and are always kept in good condition.

How to Design a Rainwater Disposal System

The shape and pattern of the gutters depend on the type of roofing. Thus, in a roof with different pitches or with a roof at different heights, the rain drainage system will also be very complex, sometimes even to the detriment of the aesthetics of the building.

Gutters are rainwater collection channels that convey them into vertical pipes called downspouts. The rainwater itself is collected by the gutters, flowing from the tiles, in the case of a pitched roof, or from the attic itself, which is given a suitable slope, in the case of flat roofs.

The gutters are fixed along the perimeter of the roof, a few centimeters apart, using dowels or storks. The fixing must be rather firm, to make the channels able to support loads consisting of atmospheric agents such as wind and snow, but also concentrated loads, such as the support of a ladder.

In order for the water to flow correctly towards the downspouts, the gutters must have a slight slope of at least 1%, i.e. one centimeter per meter of length. Downspouts used for homes have a diameter of between 60 and 120 mm. In particular, the greater the distance between the pipes, the greater their diameter. Their fastening system consists of a collar that rotates around the pipe and is fixed to the masonry with a dowel.

To avoid blockages, various types of filters are used, internal or external. The leaf stoppers, for example, are external filters consisting of a sort of metal cage to be positioned at the mouth of the pipes. The internal filters are instead placed inside the pipes, to collect and filter the debris.

Materials for Gutters and Downspouts

The piping system formed by gutters and downspouts can be made with various types of materials:

• Galvanized steel
• Stainless steel
• Aluminum and its alloys
• Rigid PVC
• Copper
• Titanium zinc.

The choice of one or the other material depends on some factors such as the type of roof and the place where the building is located. In fact, it will be necessary to evaluate the local meteorological conditions and estimate the amount of rain that will have to be disposed of.  More than considering the average rainfall of the place, however, it will be useful to inquire about the maximum recorded in recent years, in order to size the channels for the worst-case scenario.

PVC is a light and easy-to-install material, very resistant to bad weather, and cheap. Its flaw, however, is the aesthetic aspect.

Copper is very resistant, in particular, it is not afraid of oxidation. It is quite expensive, but on the other hand, it is able to last a very long time, at least 30 years and even 50, if you are careful to carry out good periodic maintenance.  Aluminum represents a good solution because it is very light, resistant, and aesthetically pleasing. It is especially suited to large lengths and allows numerous profiles and a wide choice of colors. Zinc is very resistant to corrosion and cold and can last more than 50 years. However, it is very expensive and difficult to implement, so it is not used frequently.

Types of Gutters

Also from the point of view of shape, various types of gutters can be found on the market. The most common because they are also simple to hook up is the semi-round ones, with an arched profile. Then there are the square profile gutters, used above all in cottages. On the other hand, corrugated gutters are straight at the base and wavy in the exposed part, so they are very useful for obtaining particular profiles suitable for classic buildings.