Yes. The landlord is only allowed to come into the flat without giving written notice of the visit if you agree to let him/her in or if there is an emergency they need to attend to (eg. flooding, broken pipes, gas leak etc.).

If you do not agree to let them in and there is no emergency then they must give you written notice that they want to come over. If the landlord wants to come to inspect repair work you have done or inspect the house they must give 48 hours notice. If they need to come to do repairs they must give you 24 hours notice.

The landlord can only visit between 8 am and 7 pm. All these limits on when and how your landlord can come into the flat are contained in the Residential Tenancies Act. They apply to your landlord even if it is not written in your tenancy agreement and even if you do not have a written agreement.