Police are appealing for information about a suspicious fire which led to up to 12 houses being evacuated.
Firefighters were called to an empty terraced house on Caerau Road, Maesteg, Bridgend, at 0135 BST on Wednesday.
Police believe someone forced open the basement rear door of the three-storey building, started the fire and left.
South Wales Police Det Sgt Paul Mason, of Bridgend CID, said the blaze caused extensive damage to a number of houses in the terrace but no-one was injured.
A joint investigation with South Wales Fire and Rescue Service has begun to find the cause of the blaze.
Anyone with any information about the incident is asked to contact Bridgend CID on 101 or the independent charity Crimestoppers on 0800 555 111.