It is possible for a landlord and tenant to agree on a temporary rent reduction for a specific period or event. For example, if the tenant has an accident and is on reduced income, or because the landlord is doing building work that disturbs the tenant. The rent automatically goes back to its original level when the agreed period ends and is not considered to be a rent increase (s 24A RTA).
A rent reduction doesn’t require a notice period before it takes effect. The details of it will be according to what is decided between the landlord and tenant.
Some landlords may offer a reduction in rent instead of doing repairs that are their responsibility - for example, fixing a leaky pipe or a broken stove. Tenants should be advised not to accept a rent reduction in these situations. Generally the savings are not worth the lower quality housing that the tenant is getting.
Tenancy Services provides some tips on negotiating rent.