Five fire engines and around 35 firefighters were called to a fire at a building under construction on Blackheath Road in Greenwich.
Part of the wall cavity between the third and fourth floors of the building was damaged by fire. Twelve construction workers left the building before the Brigade arrived. There were no reports of any injuries.
Station Commander Lisa King, who was at the scene said: "Around 28 square metres of the wall cavity was alight.
"Crews used specialist cutting gear to gain access between the brickwork and remove insulation in order to bring the fire under control."
The Brigade was called at 1231 and the fire was under control by 1431. Fire crews from Deptford, Lewisham, Lee Green, East Greenwich and Peckham fire stations attended the scene.
The Brigade's Fire Investigators believe the fire was caused by a gas torch being used for hot works, which ignited insulation within the wall cavity.