In general, no, but this is a heavily qualified "no", and is subject to the conditions and limitations in the planning and development legislation, some of which are noted below:
From:
http://www.irishstatutebook.ie/2001/en/si/0600.html
STATUTORY INSTRUMENTS.
S.I. No. 600 of 2001.
PLANNING AND DEVELOPMENT REGULATIONS, 2001
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SCHEDULE 2
Article 6
Part 1
Exempted Development — General
Column 1
Description of Development
Class 1
The
extension of a house, by the construction or erection of an extension (including a conservatory) to the rear of the house or
by the conversion for use as part of the house of any garage, store, shed or other similar structure attached to the rear or to the side of the house
Column 2
Conditions and Limitations
1. (a)
Where the house has not been extended previously, the floor area of any such extension shall not exceed 40 square metres.
(b) Subject to paragraph (a), where the house is terraced or semi-detached, the floor area of any extension above ground level shall not exceed 12 square metres.
(c) Subject to paragraph (a), where the house is detached, the floor area of any extension above ground level shall not exceed 20 square metres.
2. (a)
Where the house has been extended previously, the floor area of any such extension, taken together with the floor area of any previous extension or extensions constructed or erected after 1 October 1964, including those for which planning permission has been obtained, shall not exceed 40 square metres.
(b) Subject to paragraph (a), where the house is terraced or semi-detached and has been extended previously, the floor area of any extension above ground level taken together with the floor area of any previous extension or extensions above ground level constructed or erected after 1 October 1964, including those for which planning permission has been obtained, shall not exceed 12 square metres.
(c) Subject to paragraph (a), where the house is detached and has been extended previously, the floor area of any extension above ground level, taken together with the floor area of any previous extension or extensions above ground level constructed or erected after 1 October 1964, including those for which planning permission has been obtained, shall not exceed 20 square metres.
3. Any above ground floor extension shall be a distance of not less than 2 metres from any party boundary.
4. (a) Where the rear wall of the house does not include a gable, the height of the walls of any such extension shall not exceed the height of the rear wall of the house.
(b) Where the rear wall of the house includes a gable, the height of the walls of any such extension shall not exceed the height of the side walls of the house.
(c) The height of the highest part of the roof of any such extension shall not exceed, in the case of a flat roofed extension, the height of the eaves or parapet, as may be appropriate, or, in any other case, shall not exceed the height of the highest part of the roof of the dwelling.
5. The construction or erection of any such extension to the rear of the house shall not reduce the area of private open space, reserved exclusively for the use of the occupants of the house, to the rear of the house to less than 25 square metres.
6. (a) Any window proposed at ground level in any such extension shall not be less than 1 metre from the boundary it faces.
(b) Any window proposed above ground level in any such extension shall not be less than 11 metres from the boundary it faces.
(c) Where the house is detached and the floor area of the extension above ground level exceeds 12 square metres, any window proposed at above ground level shall not be less than 11 metres from the boundary it faces.
7. The roof of any extension shall not be used as a balcony or roof garden.
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Restrictions on exemption.
9. (1) Development to which article 6 relates shall not be exempted development for the purposes of the Act—
(a) if the carrying out of such development would—
(i) contravene a condition attached to a permission under the Act or be inconsistent with any use specified in a permission under the Act.
(ii) consist of or comprise the formation, laying out or material widening of a means of access to a public road the surfaced carriageway of which exceeds 4 metres in width,
(iii) endanger public safety by reason of traffic hazard or obstruction of road users,
(iv) except in the case of a porch to which class 7 specified in column 1 of Part 1 of Schedule 2 applies and which complies with the conditions and limitations specified in column 2 of the said Part 1 opposite the mention of that class in the said column 1, comprise the construction, erection, extension or renewal of a building on any street so as to bring forward the building, or any part of the building, beyond the front wall of the building on either side thereof or beyond a line determined as the building line in a development plan for the area or, pending the variation of a development plan or the making of a new development plan, in the draft variation of the development plan or the draft development plan,
(v) consist of or comprise the carrying out under a public road of works other than a connection to a wired broadcast relay service, sewer, water main, gas main or electricity supply line or cable, or any works to which class 25, 26 or 31 (a) specified in column 1 of Part 1 of Schedule 2 applies,
(vi) interfere with the character of a landscape, or a view or prospect of special amenity value or special interest, the preservation of which is an objective of a development plan for the area in which the development is proposed or, pending the variation of a development plan or the making of a new development plan, in the draft variation of the development plan or the draft development plan,
(vii) consist of or comprise the excavation, alteration or demolition (other than peat extraction) of places, caves, sites, features or other objects of archaeological, geological, historical, scientific or ecological interest, the preservation of which is an objective of a development plan for the area in which the development is proposed or, pending the variation of a development plan or the making of a new development plan, in the draft variation of the development plan or the draft development plan, save any excavation, pursuant to and in accordance with a licence granted under
section 26 of the National Monuments Act, 1930 (
No. 2 of 1930 ),
(viii) consist of or comprise the extension, alteration, repair or renewal of an unauthorised structure or a structure the use of which is an unauthorised use,
(ix) consist of the demolition or such alteration of a building or other structure as would preclude or restrict the continuance of an existing use of a building or other structure where it is an objective of the planning authority to ensure that the building or other structure would remain available for such use and such objective has been specified in a development plan for the area or, pending the variation of a development plan or the making of a new development plan, in the draft variation of the development plan or the draft development plan,
(x) consist of the fencing or enclosure of any land habitually open to or used by the public during the 10 years preceding such fencing or enclosure for recreational purposes or as a means of access to any seashore, mountain, lakeshore, riverbank or other place of natural beauty or recreational utility,
(xi) obstruct any public right of way,
(xii) further to the provisions of section 82 of the Act, consist of or comprise the carrying out of works to the exterior of a structure, where the structure concerned is located within an architectural conservation area or an area specified as an architectural conservation area in a development plan for the area or, pending the variation of a development plan or the making of a new development plan, in the draft variation of the development plan or the draft development plan and the development would materially affect the character of the area,
(b) in an area to which a special amenity area order relates, if such development would be development:—
(i) of class 1, 3, 11, 16, 21, 22, 27, 28, 29, 31, (other than paragraph (a) thereof), 33 (c) (including the laying out and use of land for golf or pitch and putt or sports involving the use of motor vehicles, aircraft or firearms), 39, 44 or 50(a) specified in column 1 of Part 1 of Schedule 2, or
(ii) consisting of the use of a structure or other land for the exhibition of advertisements of class 1, 4, 6, 11, 16 or 17 specified in column 1 of Part 2 of the said Schedule or the erection of an advertisement structure for the exhibition of any advertisement of any of the said classes, or
(iii) of class 3, 5, 6, 7, 8, 9, 10, 11, 12 or 13 specified in column 1 of Part 3 of the said Schedule, or
(iv) of any class of Parts 1, 2 or 3 of Schedule 2 not referred to in subparagraphs (i), (ii) and (iii) where it is stated in the order made under section 202 of the Act that such development shall be prevented or limited,
(c) if it is development to which Part 10 applies, unless the development is required by or under any statutory provision (other than the Act or these Regulations) to comply with procedures for the purpose of giving effect to the Council Directive,
(d) if it consists of the provision of, or modifications to, an establishment, and could have significant repercussions on major accident hazards.
(2) Sub-article (1)(a)(vi) shall not apply where the development consists of the construction by any electricity undertaking of an overhead line or cable not exceeding 100 metres in length for the purpose of conducting electricity from a distribution or transmission line to any premises.