A museum extension nearly 15 years in the making will finally be completed when the Swiss National Museum in Zurich opens its new wing to the public on 1 August 2016.

The new wing is formed by a modern and minimalist geometric volume designed by Basel practice Christ & Gantenbein. It was commissioned following an international design competition in 2002, but a period of consultation and political negotiation followed and full construction work did not begin until a decade later.

The new wing is directly coupled with the original U-shaped building – designed by architect Gustav Gull and opened in 1898 adjacent to the city’s Platzspitz Park – to create a single loop and form “an architectural ensemble of urban space.”

The towers and spires on the roof of the old building set the theme of the new structure, which features expressive folds in its rooftop, and its strong stone walls are echoed in the new wing’s 80cm thick walls. The similarities continue with the use of tuff concrete in the extension to reflect the facade of the old building, and polished concrete floors which provide a modern interpretation of the original’s decorative terrazzo floors.

“As different as the new and old buildings are, their similarities and shared architectural attributes are abundantly apparent and serve to create a unity of old and new,” said the architects in a statement.

Facilities housed in the 7,400sq m (79,600sq ft) extension include a library, an auditorium for public events, a bridge spanning across a new garden and inner courtyard, and exhibition space housed in concrete halls inspired by the city’s factories.

An official opening celebration will take place in July 2016, coinciding with the completion of remodelling to the original building – which will see the museum’s foyer, shop and restaurant renovated and a new public plaza added near the entrance.

The total cost of new wing and renovations is CHF111m (US$109m, €100m, £76m).

The client was the Federal Office for Buildings and Logistics, the general contractor was ARGE Generalplaner SLM Proplaning and the landscape designer was Vogt Landschaftsarchitekten.

The first events hosted in the new halls will be Europe in the Renaissance, exploring “new horizons in thinking, transformations and cultural interaction over great distances and time”, and an exhibition exploring Switzerland’s archaeological heritage.

Despite the ongoing renovation and construction work, the Swiss National Museum received 230,527 visitors in 2015, a record for admissions.

After the new wing is opened, renovation work will begin on the historic west wing and tower. The museum will finally open in its entirety in 2020.