It’s “market rent”
Not
“Fair market level” which does not exist
In fact the legislation does not use either of these terms as far as I can see.
I refer to
https://data.oireachtas.ie/ie/oireachtas/act/2026/3/eng/enacted/a0326.pdf
It's very complicated to follow because it amends previous legislation. But what I pasted below are what appear to be the relevant sections.
These state that a registration of a new tenancy has to (a) explain the rent level and (b) refer to 3 comparable properties from the rent register.
So far as I can tell, it does not state what is the legal obligation of the new rent level
regarding these 3 comparable properties. For example, what happens if a new rent level is above these comparables - whether or not that "disallowed" in any sense. However one can think that the clause 6.(iii) implies you have to justify the new rent level with references to these 3 comparable properties. You could presumably offer a justification of a new rent level also with regard to other evidence, e.g. daft.ie printouts, other rents you have evidence of (such as commercial data), but this could easily become a topic of push-back by the RTB.
Note there is no reference to "permitted limits" or anything of the sort.
I fully expect that once the RTB starts to flag rents which are in their view, as they say, "out of kilter with permitted levels", there will be cases that will establish some precedents, but currently we are in unknown territory. I also expect that if the RTB are heavy-handed about this, sooner or later there will be a legal action on the topic. My instinct is that the RTB will take a interpretation of the legislation that
might not stand up to a legal challenge, for many reasons which are documented in this forum, such as the fact that the rent register is by definition "lagging the market", contains many RPZ properties, and so on. But the RTB will fight it hard, that's for sure.
Another observation. This legislation does not define how the rent register query should work, as far as I can see. That is entirely the creation of the RTB. The filtering criteria, sorting criteria, cut-off limit of 10, etc - theese are all inventions of the RTB. I see no legal barrier to making a large number of searches on the RTB rent register, varying areas, BER levels, etc, and cherry-picking your favourites, so long as you can make a justification why they are "similar" to your own property. "Similar" is the term used in the legislation. (The RTB register query tool I made is useful in this regard to gather large number of data from the register rather than make many manual queries.)