The sentence has outraged victim advocates and those who know the teen, saying it sends a dangerous and "awful" message to other young men.
The youth was charged with two counts of sexual violation by rape and another of sexual conduct with a person under 16.
Two of the charges were representative meaning police believe the youth committed multiple offences of the same type in similar circumstances.
He was 17 when he was arrested but the first two assaults happened when he was aged between 15 and 16.
A teenager who knows the rapist was appalled at the sentence.
He said it was the talk of the school and students could not believe a repeat sex offender was not jailed.
"What kind of message does that send to girls," he said.
White Ribbon ambassador Mark Longley said the sentence was "shocking" and "not a punishment at all".
And victim advocate Ruth Money said the case would prevent other people disclosing abuse, fearing a lack of justice.
The Crown has not referred the matter to the Solicitor-General for appeal.
Until recently the youth had been attending a North Shore high school where he was a rising sports star.
He was charged last year and after a lengthy legal process - some of which cannot be reported - the youth was sentenced earlier this month in the North Shore District Court by Judge Pippa Sinclair.
She explained that the victims were all "present or past associates" of the youth.
In 2016 the youth raped a 14-year-old girl at a party after he encouraged her "to drink copious quantities of vodka".
Judge Sinclair said when the girl became "extremely intoxicated" the youth helped her to a bedroom where she fell asleep.
She woke up several times to find the youth touching her and then raping her.
"[She] had not consented to any of this sexual activity, but was too intoxicated to struggle," the judge said.
"You later sent her a text apologising."
The second victim was 15 when she was raped, and was also encouraged to drink alcohol by the youth before the assault.
The pair were at a public event and he took her into a bathroom where, despite her protesting "multiple times" he forced himself on her.
On multiple other occasions the youth and the girl were having consensual sex and he refused to stop when she told him to.
The third victim was 14 and was staying with a group of girlfriends when she was assaulted.
The youth admitted all of the offending.
But the sentencing notes do not offer any explanation or apology from him for the assaults on the girls.
Judge Sinclair said the victims had suffered significant emotional and psychological harm.
"[The victims] describe feeling happy and confident prior to your offending… Since your offending their lives have changed," she said.
"Your offending and the court process has left them scarred and distressed."
Judge Sinclair said in all cases the youth exerted control over vulnerable victims - particularly as they were intoxicated - and breached their trust.
She said his punishment had to balance the purposes and principles of sentencing alongside the youth's rehabilitation and future needs.
"I need to hold you accountable for the harm you have done and the effect your offending has had on all three victims; denounce your conduct and deter you and anyone else from offending in this way again," she said.
"I am required to consider the gravity of your offending and your particular culpability, so I am consistent with other sentencing decisions.
"I also need to be mindful of your rehabilitative and reintegrative needs, particularly given your age.
"Ultimately, I must impose the least restrictive outcome in these circumstances. "
Judge Sinclair said there was a presumption sex offenders like the youth would be sentenced to prison.
But it was up to her to consider the facts of the case and the offender's personal circumstances and determine whether jail was appropriate.
Judge Sinclair set a starting point of eight years' jail - but sliced 50 percent of that off on the basis of the rapist's age.
She gave him further discount for his early guilty plea and personal circumstances including previous good character and unblemished record, family support and willingness to engage in rehabilitation.
She said a punitive approach had to be "outweighed by the wellbeing of a young person in securing his or her future".
After Judge Sinclair applied the discounts the sentence fell to two years in total, meaning she could consider home detention.
Longley, whose daughter Emily was murdered in 2011 by her boyfriend after being in a toxic relationship, could not believe the sentence when approached by the Herald.
"Twelve months home detention is not a punishment... it sends an awful message," he said.
"To admit rape and be given 12 months at home sends the message that you can do that and the repercussions won't be very strong.
"What is the deterrence? Has he learned a lesson? Is this enough to stop this guy? It's unbelievable."
Longley said the justice system needed to change and put victims first.
Sexual harm - do you need help?
If it's an emergency and you feel that you or someone else is at risk, call 111.
If you've ever experienced sexual assault or abuse and need to talk to someone contact the Safe to Talk confidential crisis helpline on:
• Text 4334 and they will respond
• Email support@safetotalk.nz
• Visit https://safetotalk.nz/contact-us/ for an online chat
Alternatively contact your local police station - click here for a list.
If you have been abused, remember it's not your fault.
