Do I need to register with PRTB ?
Yes you do.
"every dwelling, the subject of a tenancy".
And "tenancy is defined as
‘‘tenancy’’ includes a periodic tenancy and a tenancy for a fixed term,
whether oral or in writing or implied, and, where the context so
admits, includesa sub-tenancy and a tenancy or sub-tenancy that has
been terminated;"
What happens if I do not register ?
As far as my memory goes, I think a fine of up to 2,500 euro (might be 5,000) and or imprisonment.
Also, if you are not registered, you are unable to make a claim or counterclaim against a tenant who makes a claim against you.
If there are 3 or 4 tenancies in a year do you pay 90 euro each time?
Yes.
The tenancy registration includes the duration of the tenancy so the PRTB knows how long. However, a fixed term tenancy is usually of 12 months and, if the tenants remain and do not sign a further fixed term agreement, the tenancy becomes a Part 4 tenancy and the tenant may remain for a total of 4 years without signing a new agreement.
You could quite simply have a 12 month Part 4 (or a fixed term tenancy with an "out" clause so the tenants may leave)tenancy which allows the tenans to vacate at any time by giving the correct amount of notice. Going this route, you could have an assignment so that the tenant leaving passes or assigns his rights to someone who takes over that part of the tenancy. This way, you only have to notify the PRTB of a change of tenant/s and no fee is incurred.
However, IMHO, you would have less hassle using a Part 4 tenancy.