Renovation on London's Olympic stadium is set for a price increase of £50m as the construction company responsible believes the task is much bigger than first thought.

Construction Enquirer magazine revealed that building firm Balfour Beatty, who has been contracted to refurbish the stadium, asked the London Legacy Development Company (LLDC) for the extra funds because of how complex it will be to extend the roof of the stadium to cover retractable seating over the running track.

If the £50m is granted to Balfour Beatty, it will take the total cost of the renovation of the Olympic Stadium, which Premier League team West Ham is set to move into in 2016, to more that £600m – more than double the original £280m budget that it was allocated.

A spokesperson for E20 Stadium, the partnership managing the stadium renovation, told The Guardian: "The project still has close to two years to run and we are in no doubt Balfour Beatty can deliver the programme as planned. This is a complex project and there are always ongoing discussions about specific elements within it."

West Ham however will not have to fork out anymore after they agreed a fixed £15m contribution when the club won the 99 year lease to the stadium after competing against Leyton Orient and Tottenham Hotspur.

Newham Council will pay £40m towards the work, the Department for Culture, Media and Sport and the Department for Communities and Local Government will put in £38.7m, and £25m will come from government money, with LLDC footing the rest of the bill.

The refurbishment will temporarily halt next year when the stadium hosts five Rugby World Cup matches next summer.