The Judge, Mr Philip Richards, said the fire was a "very irresponsible act" with "consequences that were devastating". He acknowledged that Mr Goulding has considerable learning difficulties which is why he took so long to accept responsibility.
Mr Goulding has been remanded in custody and will be sentenced tomorrow at 2pm at Newport Crown Court.
More top news
A man from Cardiff, killed in a drone strike after travelling to fight for IS, has been described as a "prolific recruiter" in a new report.
Leeds forward Stevie Ward says he could play for Wales in the World Cup - but insists he wants to force his way into the England set-up.
Two hundred officers were involved in a raid this morning, which saw 20 people arrested.