You neighbour may be availing of the exempted development schedule.
This is set out in
S.I. 600 of 2001 http://www.irishstatutebook.ie/2001/en/si/0600.html
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.
Conditions
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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As amended by
S.I. 235 of 2008 http://www.irishstatutebook.ie/2008/en/si/0235.html
CLASS 50(a)
The demolition of a building, or buildings, within the curtilage of— (i) a house, (ii) an industrial building, (iii) a business premises, or (iv) a farmyard complex.(b) The demolition of part of a habitable house in connection with the provision of an extension or porch in accordance with Class 1 or 7, respectively, of this Part of this Schedule or in accordance with a permission for an extension or porch under the Act.
Conditions
1. No such building or buildings shall abut on another building in separate ownership.2.The cumulative floor area of any such building, or buildings, shall not exceed: (a) in the case of a building, or buildings within the curtilage of a house, 40 square metres, and (b) in all other cases, 100 square metres.3. No such demolition shall be carried out to facilitate development of any class prescribed for the purposes of section 176 of the Act.
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There are other parts of the Acts and Regulations which can and do affect and mitigate this, including the Land Conveyancing Law Reform Act, 2009.
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http://www.oireachtas.ie/documents/bills28/acts/2009/a2709.pdf
This Act has not been tested to any great degree in case law yet as far as I know.
Chapter 3, pp 38-43 including Sections 43 to 47 inclusive seem to bring in some revolutionary concepts of how to deal with Party Wall matters.
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In relation to unauthorised use, unless you want to retain an archtiect or planning consultant to do the work for you, you could look up the planning file of the previous application that was refused and find out who the person was at that time.
Then you could write to him or the builder on site to see what's what - failing this you could refer the matter to Planning Enforcement to see if a breach is occurring and to the Health and Safety Authority to see that all matters are being done correctly on site.
Its better in my opinion to retain a professional to advise you in these matters - planners and the HSA don't appreciate time-wasters or cranks and a simply site inspection wil inform a good planning consultantor architect allied to a planning file inspection and a chat to the local planning officer.
A set of photos and a written report/query to the planning officer, plus say two site inspections should set you back no more than say €500.
With regard to your neighbour, assuming he is availing of the Exempted development schedule as amended; -
The 40 sq.m. can be entirely on one level or can hace up to 12 sqm on 1st floor if terraced.
Keeping back from the boundary is good practice in the absence of an agreement.
Ground floor windows must in general be more than 1.0M back from the boundary.
However these two parts of S.I. 235 of 2008 quoted above are intriguing because of the letter and intent of the law, which seems unclear:
"The demolition of part of a habitable house in connection with the provision of an extension or porch in accordance with Class 1 or 7, respectively, of this Part of this Schedule or in accordance with a permission for an extension or porch under the Act."
AND
"1. No such building or buildings shall abut on another building in separate ownership."
Does this mean people cannot demolish part of a terrace to extend it, as your neighbour appears to have done?
A literal interpretation suggests this might be the case.
I cannot comment more on AAM because each development is different and there may be many other factors involved.
Sorry to hear you appear to have grumpy neighbours.
FWIW
ONQ.
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All advice on AAM is remote from the situation and cannot be relied upon as a defence or support - in and of itself - should legal action be taken.
Competent legal and building professionals should be asked to advise in Real Life with rights to inspect and issue reports on the matters at hand.