From Revenue:
'New large houses/apartments without a floor area compliance certificate
Section 92 of the Stamp Duties Consolidation Act 1999 provides for a relief from stamp duty for owner-occupiers of new houses/apartments. The stamp duty is charged on the site value or one quarter of the total value of the property (less VAT) whichever is the greater.
The relief will only apply where the floor area of the house is greater than 125 sq. m. and is so certified by a qualified architect, engineer or surveyor, as set down in regulations (Housing (Floor Area Compliance Certificate Inspection) Regulations, 2004 (SI 128/04)) made by the Minister for the Environment, Heritage and Local Government. '
If the site value or quarter of the total value, whichever is greater, is less than 125000, no stamp duty applies.