If you only need housing for a few months, for example due to plumbing renovation, you can apply for short-term housing.

Apply for short-term housing
We offer short-term rental housing for temporary housing needs. You may receive short-term rental housing if you need to live away from your home for a few months due to, for example, a plumbing renovation, work assignment or practical training.
Short-term rental housing are non-subsidized rental apartments owned by the city of Helsinki. There are no income or wealth limits in the selection of tenants. You can also continue your rental agreement after the short-term stay if you wish to stay in the apartment.
Apply for a short-term apartment through Oikotie.fi (in Finnish)(Link leads to external service)
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Heka rental apartments are specifically intended for people with low income and a need for housing.
Tenant selection for non-subsidised rental apartments does not consider income or wealth limits. You may get an apartment quickly.