Vancouver's One Wall Centre is having its windows replaced at a cost of $7 million, in one of the most complicated construction projects currently underway in the city.

The clear glass on the top 17 residential floors of the building on Burrard Street will be replaced with darker glass to match the 31 hotel floors below.

The work requires the building of a unique "ring" platform around the 48-storey tower, which is the third tallest building in Vancouver.

The custom-made platform weighs more than 8,000 kilograms and will move down the tower as the windows are replaced, powered by 18 motors.

The method has never been used before, as most window replacements require scaffolding and netting around the entire building. The new system means businesses on the ground floor at the Sheraton Hotel will not be disrupted.

The windows will be brought up individually in a residential elevator, then taken through the suites, before being passed through to the platform and attached to the building.

Around 1,500 glass units are due to be installed, the largest weighing more than 200 kilograms.

Tenants' dispute

The building had to be constructed with two types of glass after the city stopped work on the project while it was being built in 2000 because of a dispute over what type of glass was approved for the project.

The city maintained it had an agreement with the developer that it would be glazed with translucent glass, not black. Eventually a compromise was reached and a translucent glass was used to finish the upper floors of the building.

But in 2011, the residents' strata corporation filed a lawsuit claiming the translucent windows were leaking air, causing them to fog up.

Residents also complained the coating on the windows did not reduce the heat inside the suites as effectively as dark glass, some measuring temperatures of 42 C at their windows, even with air conditioning.

The cost of the window replacement is being shared by the developers and owners.

With files from the CBC's Kirk Williams.