For the past few years it has been generally accepted that Saudi Arabia’s Jeddah tower will replace Dubai’s Burj Khalifa as the world’s tallest building.

The tower, which is expected to be 1,008 metres tall when completed, has had no real rival scheme, and as the China demand-fuelled global commodity super cycle comes to an end it appeared unlikely that the tower would have any challengers for the foreseeable future.

Dubai seems to have other ideas. On 10 April, Emaar Properties chairman said that Dubai’s new Calatrava-designed tower will be a “notch” taller than the 828 metre-tall Burj Khalifa adding that the height will remain a secret until it completed ahead of the 2020 Expo.

Alabbar’s comment raises several key questions on what will be the world’s tallest building. The first question is what does a notch mean? Did Alabbar mean just a little taller or a lot taller?

If he meant a lot taller, is it going to be the world’s tallest building? If he meant just a little taller, was he deliberately underplaying the height so that extra metres were not added to the rival tower in Jeddah? Having successfully built the world’s tallest tower before, both options are possible.

Then comes the question of scheduling. After securing funding in December last year, Jeddah Economic Company, which is developing Jeddah Tower, expects the project to be completed on time in 2018.

The Dubai tower is due to be completed ahead of the 2020 Expo, which means it could be completed about a year after Jeddah Tower giving it a distinct advantage if it needs to increase its height. This should not be overly difficult to achieve as the tower’s height is achieved with a slip-formed concrete core, which should be relatively easy to extend if some extra metres are needed.

The steel structure sitting on top of the core and the tower’s spire could also be extended.

The advantage Dubai would have in this scenario assumes that the Jeddah Tower will be completed on schedule.

When Jeddah Economic City secured funding in December it said the tower had reached the 26th floor. Based on earlier presentations made by the company on the construction programme for the tower, it should have reached level 85 in December 2015.

Although it is not clear whether this programme has changed, this suggests that in December the project was about nine months off programme, which means the December 2018 completion date could be difficult to achieve.

If the Jeddah Tower is completed about a year late, then both towers could be completed at the same time opening up a tantalising game of cat and mouse played between Jeddah and Dubai as both keep the final height of their towers closely guarded secrets.