The London flats being built above train tracks
London architects say research suggests up to 250,000 homes could be built over the capital's train tracks.
Network Rail, the body in charge of maintaining the country's rail infrastructure, says homes built in this way could help to solve the housing crisis.
But the lives of builders are not made easy by trains roaring along beneath them as they work.
They have had to come up with some plucky tactics to make sure their working environment - however bizarre - is not dangerous.