from revenue website
Over Floor Area of 125 sq. m
New houses or apartments which are purchased by an owner occupier (including a first time buyer) where the total floor area exceeds 125 square metres are charged with duty, at the appropriate residential property rate as per the table above, on the site value (excluding VAT) or one quarter of the total value of the house including the site (excluding VAT), whichever is the greater, subject to clawback.The size of the floor area must be certified by a qualified architect, engineer or surveyor