The Fire Service was called at 12.45am to Highbridge Road where an outbuilding attached to a domestic property was alight.
Crews worked to extinguish the blaze using breathing apparatus and hose reel jets. At 1am, the fire crews said all persons had not yet been accounted for.
The Incident Commander requested further appliances, taking the total of pumps to four, and all occupants were accounted for shortly after. Crews continued to tackle the fire inside and out of the property.
By 1.40am, the gas and electrics were isolated and the crew worked to strip back the roof. By 2.15am, crews began dampening down and a risk assessment was carried out. The Police were also requested to attend.
Firefighters used four breathing apparatus and two hose reel jets to extinguish the blaze.
A lean-to building sustained 85% fire damage, a kitchen 5% fire damage and a section of roof 5% fire damage. The rest of the property was slightly smoke damaged.
The cause was undeterminable, said a fire service spokesman, who added that four people had been taken to hospital for precautionary checks after being evacuated by crews.