+1 Bren88's comments.
I would add that once you are aware of tj existence of and Area of Special Amenity you would beunwise to assume that you can extend using the exempted development provisions.
In such a landscape, there may also be other restrictions, such as protected views and there is also the possibility of restrictive conditions in the original permission or restrictive covenants in any purchase contract.
Narrowing the focus and centering on the "Area of Special Amenity", you may be overlooking other restrictions which could equally mean than an extension undertaken without permission is unauthorised.
Here are some random and unchecked links which may better inform you:http://buckplanning.blogspot.com/2006/11/development-control-and-exempted.htmlhttp://buckplanning.blogspot.com/2006/11/areas-of-special-amenity-and-irish.htmlhttp://buckplanning.blogspot.com/search?q=Area+of+Special+Amenity+http://www.donegalcoco.ie/NR/rdonlyres/A26D5D06-AD30-43B5-8B6F-D73D0C97E5AC/0/exempteddevelopemtpreconditions.pdfhttp://www.wicklow.ie/apps/wicklowbeta/Publications/Planning/GreyDelganyLAP/Adopted%20Plan/GDLAP_8.pdf
The difficulty with living in a scenic area is that your wishes to develop your property may be restricted.
One resolution would be to seek a Section 5 Declaration costing €80 and taking 4 weeks or so.
This may help avoid any error arising from some local authority planning officer making an off-the-cuff comment over the phone which may prove invalid.
You may be asked to produce drawings showing the proposed development - if so, consider appointing a competent architect to prepare drawings based on your instruction.
If a permission is required, you would be well advised to ask an archtiect to design what you really want to add on or transform the dwelling - done well, it will improve amenity short term and increase eventual sale value.