Square gutters create a clear eaves line and can work well with a metal roof. However, choosing them is not just a matter of shape. The cross-section, outlets, and the method of joining and fixing all need to be checked. A square gutter can be left visible or concealed behind a fascia cover. Each system has its own details. Installation rules for a round system should not be carried over on the basis of a similar size alone. Above all, it is about a defined appearance at the eaves. A flat front face can emphasise the horizontal line of the roof and echo the rectangular layout of the windows. It suits both tile-effect metal roofing and trapezoidal steel sheet, provided the overall design is well thought out. The shape alone, however, does not automatically mean greater capacity than any half-round gutter.

Concealed gutters can suit a house with a metal roof well, especially with a simple building form and restrained eaves detail. Their selection, however, requires the drainage to be designed in advance. The masking fascia must not restrict access for cleaning, and the outlet must be matched to the roof surface area. First, the route of water, ventilation and insulation must be established. Only then is the colour of the visible elements chosen. Various solutions appear under the name concealed gutters. Sometimes only the gutter behind the masking fascia is concealed, while the downpipe remains on the façade. In another arrangement, the outlet is also concealed within a suitably prepared wall zone. These variants should not be treated identically.

Gutters for a roof covered with sheet metal are selected primarily according to the volume of water to be drained and the layout of the roof slopes. Colour and shape come next. You need the dimensions of the catchment areas, the length of the runs and a plan for the arrangement of the outlets. The gutter and the downpipe must form a compatible set. Even a large cross-section will not help if the water does not reach the gutter or if the rest of the system is blocked. It is worth planning the entire rainwater path through to the receiver. First mark on the plan which eaves the water flows to from the individual roof slopes. A simple gable roof usually divides the runoff between two sides. With dormers and roof valleys the layout can be more complex.