He and fellow neighbours called the fire service and used a garden hose to douse the blaze before help arrived.
Senior station officer Doug Bennett said the fire within a double garage alongside the house had started in two distinct locations.
The home's occupant, Di Uden, left for work at 10.45am, only to be called less than an hour later by a neighbour, who told her: "Your shed's on fire."
Ms Uden said she was grateful for her neighbours' quick responses, which helped stop the fire from spreading into the house.
Mr Rush said he has been surprised by the number of house fires in Wanganui since taking up his post in October.
He said the most common cause of those fires was cooking, followed by electrical equipment, and he urged people to be more careful.
"We have had a high number of house fires and 99 per cent have been preventable, which is quite disappointing," Mr Rush said. "It's a real concern that we are getting so many cooking fires. Stay with your cooking - if you leave it for a minute, you've got a disaster. Please - take care."
In the past fortnight there have been at least three serious house fires.
On February 11, a house on the corner of Keith and Dublin streets was extensively damaged by a fire that was believed to be started by children playing with matches, and four people were taken to hospital for treatment.
On Saturday, a woman was lucky to escape unhurt after the house she was renovating on Anzac Parade exploded in a fireball. Investigations into whether the fire was caused by vapours igniting or was deliberately lit are ongoing.
And a Peat St home was gutted by fire about 3am on Tuesday. Firefighters said the blaze was started by an unattended pot on the stove.
