If it is habitable then YES, you need permission.....
Making or widening an access onto a public road, the demolition of a structure which was last used as a residence, demolition of a building in a terrace or one which is attached to another building in separate ownership, and other works, do need permission, either separately or with the planning permission for the house.
from http://www.clare.ie/planning/faq_pl4_Building_A_House.html#a10
also see:
http://www.kerrycoco.ie/planning/pl5.pdf see section 14.
14. Can I demolish an old building?
You can demolish without permission a building other than o a habitable house, or o one listed for preservation in the local development plan or draft plan o a building in a terrace, or one which is attached to another building in separate ownership. However, it does not automatically follow that you will get permission to build a replacement. A habitable house includes a structure which was last used as a dwelling even if it is now in an unlivable condition. It also includes a building where the last permitted use was as a house, even if it has been in unauthorised use since.
from:
http://www.galway.ie/en/Services/Planning/MakingaPlanningApplication/Doingworkaroundthehouse/