At KAITEK ARCHITECTURE we believe that building well is a virtue that we must cultivate in our works.

One of the most common pathologies that we find in all the technical inspections that we have carried out over the years is the poor constructive resolution of the flashing element. This generates deficiencies in the form of stains and drips on the facade that over the years can end up with a complete deterioration of the finishing mortar of the facade, allowing the entry of water.

The rain gutter has, briefly, three fundamental characteristic elements:

• The “board”
• The dripper
• Overlaps or resolutions

What is a rain gutter for?

A gutter is a constructive element located at the bottom of a hole or at the top of a crown (on the railing of a roof) that conducts the water out and expels it so that no runoff occurs from the plane of the facade, both on the sides and on the bottom.

In this example of the image we see how the lower part of the opening has been tiled with a waterproof material, this prevents it from staining. We see that it is a rain gutter built with some prefabricated element (we suppose it will have a gutter even though we cannot see it), which has a projection on the sides to prevent water from sliding to the sides with the wind.

The elements of a rain gutter

The dripper

The gutter is the key element of a gutter since it prevents that once the waters reach the end of the gutter they return from the bottom to the façade plane.

The board

The “board” is the largest element of the gutter, it has a slight slope to evacuate the water and can be made of different types of materials (ceramic, reinforced concrete, zinc, copper, stainless steel, marble …)

The qualities that are essential are its low porosity and impermeability since water will circulate through its surface and this will facilitate its cleaning and that it does not retain water that could affect other elements with which it is in contact.

It can be built in a single piece (precast reinforced concrete pieces, for example, or folded galvanized steel sheets manufactured in a workshop, etc.) or built in pieces, this would be in the case of ceramic cladding, natural stone pieces. In the latter case, the joints between the pieces must be treated well, since they are a weak point with regard to the impermeability of the element.

Overlaps or resolutions

The overlaps with the jambs (in the openings the vertical parts of the hole), the meeting with the carpentry and the sub-frame, the lower and jamb waterproofing.

The lower waterproofing is a sheet that will protect the rest of the elements from the intrusion of water. It is appropriate that “rises” are made on the perimeters (about 15 cm on the jambs, the entire sub-frame in the meeting with the carpentry, for example) that is, that the horizontal sheet when we reach the edges is extended vertically.

What the regulations say in Spain

In Spain, a very exhaustive building regulation was approved in 2006, which refers specifically to rain gutters. It refers to the 2 cm separation from the façade plane to drive the water well, the existence of a lower waterproof barrier and the existence of the dripper element.

Also to the 2 cm lateral overlap with the jamb, in other words, the regulations suggest that the flashing be embedded 2 cm laterally into the wall.

The image that we put below is extracted from the CTE (Technical Building Code) version of 2016.

Constructed examples

Where best they build this type of element, it is better for them due to how much it rains throughout the year, it is in the Nordic and Central European countries. The photos that we put below are from Munich and Helsinki and have been taken by us during the trips we have made.

Example 1. Munich (Germany)

This photo below represents a perfect flashing design, it must be built about a century ago. Although it is aged by time, it has all the elements well executed: the overlap with the jamb, the length of the flight, the drip (although it is not appreciated it is a fold that makes the sheet return up) the board is a single piece of copper treated with what the impermeability is total.

Example 2. Porvoo (Finland)

This flashing is located in a Church church in the municipality of Porvoo in Finland. The building began to be built in the thirteenth century and as we see the design of its gutters (probably the pieces have been changed at some point) it continues to work perfectly.

Example 3. Helsinki (Finland)

The exception to the rule, don’t try it at home. In the image below you can see the facade designed by Alvar Aalto (the best Finnish architect of all time) for the Enso-Gutzeit headquarters building. Here the gutter becomes part of the façade itself (capialzado, jambs and gutter become equal pieces) and a waterproof material (polished marble) is used. Even so, to avoid runoff along the façade plane, some horizontal joints appear that act as drippings. Guess where they are!