A teenager has been jailed for more than two years after torching an elderly Auckland woman's home in an effort to "smoke her out", beat her and rob her.

Tristan Taylor, 18, was sentenced today in the Waitakere District Court to two years and four months' imprisonment for an arson he committed, while breaching bail, that caused about $23,000 of damage.

The court heard how at the time of the fire Taylor had been on bail for assaulting a woman and threatening to stab her and a friend in November last year.

On January 7, the day of the fire, Taylor and a group of friends went doorknocking in Ranui hoping to distract the occupants long enough to steal property from homes.

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At the home of a 88-year-old widow's the co-accused, whose case was before the Youth Court, asked for a glass of water but then allegedly kicked a door and broke a window.

Taylor was outside the property but was aware the group had been asked to leave, the court heard.

Later, the teens returned to the woman's house with a plan to start a fire to flush the pensioner out of the house.

Taylor was encouraged to set a fire inside the house through the broken window.

Luckily, the woman, who lives alone, was in another part of the house but she was "hard of hearing".

She was uninjured in the blaze and firefighters were able to contain the fire and save her home. Taylor had also returned to the fire to try and help.

Explaining his actions to police, Taylor claimed he had been threatened with a tyre iron by one of the group who wanted him to set fire to the home.

Judge Kevin Glubb said the level of premeditation shown was an aggravating factor.

"This is in my assessment, was significant ... smoking her out of her house, and beating and robbing her - that was the plan."

It was fortunate that the plan failed, he said.

The elderly woman has been left in shock following the fire and has struggled to sleep, fearing the group would return, the judge added.

"She notes you have been in custody and she is hopeful you will remain there."

Judge Glubb accepted that Taylor, who pleaded guilty at the earliest opportunity, was genuinely remorseful for the offending and the fact he returned to help "shows you have a conscience".

"If you could take it back, you would."

In a letter before the court, Taylor wrote that he wanted to reassure his victim that he posed no threat to her in the future.

However, Crown prosecutor Sam Teppett said Taylor returning to help had limited significance as a mitigating factor, calling the teen the "fire-starter".

"He was the one who gathered the newspapers and lit the fire in the first place.

"He knew that he wasn't supposed to be on the property."

Teppett said the extent of damage to the house was about $23,000, which was covered by insurance.

The damage to personal belongings amounted to about $1000.

Defence lawyer Susan Giles said her client accepted responsibility for lighting the fire.

"The co-offenders are equally responsible, and quite rightly described as the co-offenders," she added.

His actions afterwards were a significant mitigating factor because in that instance Taylor had put the victim's needs above his own, she said.

If he had not returned "he might not have been identified as the offender", she said.

Giles conceded that the starting point would be imprisonment but said it should be short-term so not to be "crushing" for the young man.

Rather, she said, it should be one that "allowed him to see the light at the end of the tunnel".

After the house fire, the victim - a devout Catholic - told the Herald she hoped the accused would be found so they could get much-needed help.

"I'm not long for this world but these kids desperately need help," she said.

At the time police described the arson attack as an "appalling crime".

When sentencing Taylor, Judge Glubb said: "It gives me no pleasure to send you to jail today."

A further two months would be served concurrently for the other charges of assault, possession of a drug utensil and speaking threateningly.

Taylor will serve his time alongside youths.