Aittokoski was designed by architect Aarne Ervi and built soon after Ämmä Hydropower Plant by Oulujoki Power Company and the construction lasted from 1958 to 1960. It is the largest of the three power plants in the River Emäjoki and has a capacity of 45 megawatts.

The construction of the forebay required large scale earth moving works. Because of the composition of the soil, as in Montta, the Icos Veder -method had to be utilized to condense the ground. The construction site also dictated the overall composition of the power house. In Aittokoski the power house is built in a 30 metres deep chasm inside the bedrock, which gives the building its vertical, tower-like, shape and also dictates its program. Aittokoski is the only power plant where the draft tube runs completely underground while the gate room is located up on the same level as the head water. Aittokoski is also the only power plant where the inflow is controlled by a radial gate. Despite the challenging construction site, Ervi was able to bring natural light into the building, using the openness of the interior space and carefully placed windows and reflecting surfaces.

The program of the power house is composed around the machine hall that sits at the bottom floor. The service level is built as a mezzanine that circles the machine hall bay. Spiral staircase leads up to the shallow gate room on the upper floor. The offices and control rooms are located below the service level. Black and white -striped clinker tile on the floor and the dramatic blue and yellow dominate the appearance of the interior, while the generator is painted red. Ervi also refined the interior with structural details like the corbels supporting the beams above.

The building’s on-site casted concrete frame was completely cladded with profiled aluminium sheeting giving it a drastically different appearance from Ervi’s other power houses. An additional concrete framed service space was built on the eastern side of the power house while the concrete structured log crane and the regulating dam are located on the western side of the power house. The combination of aluminium and concrete gives the facility a striking and powerful industrial appearance. The verticality of the building can only be realized by viewing the building from the deep canyon where the tailrace runs. This is a dramatic difference compared to the view from the forebay, where the whole facility is barely visible.

Text: Samuli Paitsola