As a non-resident landlord, if you let directly to a tenant, the tenant will have to withhold basic rate tax from the rent due to you, and pay this over to the Revenue.
However, if you appoint an agent (could be friend or family), and they register for tax as an agent, they will collect the tax (gross for you) and pay this over to you directly, thus having no withholding tax. However, the Revenue usually reccommend that the agent withhold a certain amount if there is going to be a tax liability, as they will be liable to pay this!!
If you want any more information about this please PM me.