The RTB have stated that as long as at least one original tenant remains, the original lease remains in place. I'm assuming this has a legal basis, so in your scenario, the tenant would win hands down.
I would caution using the term "lease".
Legally, the lease is a contract between the landlord and tenant(s). It is not the tenancy.
The lease is binding on tenant and landlord, but any terms that violate the RTA are effectively unenforceable.
The tenancy comes into existence separately from any contract/lease.
When you give the keys to the tenant and they take possession of the house, the tenancy materializes. You might be able to argue that the lease says that happens on a specific date, but it happens due to the operation of law and not due to any signatures.
If you create a landlord/tenant relationship, then the tenancy appears automatically. For absolute safety, the best plan would be to have the lease state the handover date.
"The tenants agree to take possession of the dwelling at XYZ on the xth of month. Failure to take possession on that date shall terminate this agreement.".
Then the landlord meets them on the date in question and goes into the house with them. He then gets them to sign a statement that they accepted the keys on that date.
That way there is no disagreement about when the tenancy starts. The tenancy starts when the keys are handed over. Under no circumstances should the tenant be allowed to do anything tenant-like before that moment.
This may become more important as exact dates start to matter.
Though, if you did have that clause, you need to make sure to get them to sign a statement saying they took possession.
I would think that so long as one original tenant remains, the original lease remains.
I believe that is the case. You can't rent rooms in Ireland. Ironically, the "rent-a-room" scheme is not actually a scheme to rent out rooms (it is for paid lodgers).
Thinking about nightmare interpretations.
A landlord wants to rent a house with 4 rooms for 2000 a month. He decides to rent each room for 500 with shared use of the common areas.
Tenant A agrees and moves in to room 1 and pays 500 per month (lease A).
Tenant B agrees and moves in to room 2 3 months later and also pays 500 per month (lease B).
I think legally, a tenancy for the whole house materializes when tenant A moves in. There is no separate tenancy created for tenant B. Lease B is just an agreement between the landlord and tenant B. It doesn't create a tenancy.
Now, the question is what to do about rent setting.
I think the tenants could argue that the tenancy has an agreed rent of 500 per month. Adding the 2nd tenant doesn't allow any change to the rent. In any case, the landlord didn't go though the formal rent setting process.
Even if he did, an increase from 500 per month to 1000 per month for the whole house is clearly more than 2% per year (not to mind the inflation rate cap). They could demand he reduce the rent to 500 per month and they both pay 250.
The only thing the landlord could do is add more tenants to bring the house to 4, but he would still be capped at 500 per month (+2% per year). He can also block more tenants.
Probably depends, did tenant C sign the lease?
If not, then I expect the original lease is over after the original signees exit.
No, the tenancy and lease are completely separate things. The lease might slightly interact, but mostly the tenancy wins if there is disagreement.
You don't need a lease to be a tenant, it materializes automatically. Once you are given possession of the house in a tenancy-like context, it springs up.
There is a whole part of the RTA that handles adding new tenants.
Anyone who lives in a dwelling for more than 6 months is entitled to be added to the tenancy. The landlord can't block it if that would be "unreasonable". What counts as unreasonable is not defined.
So, C above would be entitled to be a tenant once he was there for 6 months. It is like the 6 months probationary period for tenancies.
Doesn't C acquire tenancy rights after 6 months residence independently of the original lease?
Exactly. Though he does need the landlord to formally add him, but the landlord has to do it (or argue that the refusal wasn't "unreasonable").