It's not just the Landlord that has a duty, the occupiers have too.
See "Propety Owners/Occupiers" part of the following:
http://www.environ.ie/en/Environment/Waste/LitterPollution/PublicationsDocuments/FileDownLoad,1508,en.pdf
So for that part of the problem you don't have to find the Landlord, they are responsible for it themselves and can be fined.
Likewise, they are not absolved from responsibility of Anti Social behaviour just because they are renting. I'd like to see that defence in any court. "Sorry your Honour but I'm not responsible for blasting music after 11 pm. It's the Landlord's fault, because he rented to us" Uh, I don't think so
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So, personally, whilst it would be great if you could find the Landlord and give him an earful, at the present moment in time, I would concentrate on getting the issues resolved that effect you.
By law you are entitled to the peace and enjoyment of your own home. Whether he thinks its a waste of paper writing to him, is irrelevant and I don't mean that to sound curt. What's important is that you can show you tried to resolve the matter through documentary evidence. Believe me if you start now, you will be so glad you did.
If the local community Garda will not listen to you, you go over his head and ask to speak to the Super. But before you do, as I said, make sure you have your evidence of a registered letter to the Occupier & your photos. They won't be long about taking you seriously when they realise how serious it is to you, to have gone to that amount of trouble.
See also "Criminal Justice (Public Order) Act, 1994" at the following link: