A fire tore through the iconic medieval building last April, destroying its roof and spire but leaving its structure intact.
President Emmanuel Macron later vowed to restore the building within five years.
The global coronavirus pandemic forced officials to delay the planned start of reconstruction on 23 March.
But on Monday, workers returned to the construction site to make it compliant with new social distancing rules.
Monsignor Patrick Chauvet, the rector at Notre-Dame, says this includes modifying changing rooms and showers for workers.