Is my neighbours’ big extension exempt from planning permission?

Property Clinic: After they drilled along the internal dividing wall, we’ve also been able to hear far more noise from their house, including their conversations

My next-door neighbours have built a rather large extension to the rear of their semidetached house. They say it is exempt from planning permission, but I’m not so sure.

After they moved in, about 15 years ago, they replaced the previous owners’ wooden shed with a brick-built utility room, complete with pitched roof. They then converted their attic into a living space with a bathroom. After that they built the extension, which is joined to the party wall and is much higher than the wall and our conservatory, which was built long before they moved in. Next they erected a lean-to with decking at the end of the garden (which is not especially big) and finished up by covering over the side passageway to their house.

I’d like to know how much of this counts when calculating the 40sq m (430sq ft) allowed without planning permission. Also, how is the 25sq m (269sq ft) that should be left open calculated? Is the lean-to regarded as a structure or “open” ground?

The extension and passage covering may give rise to health-and-safety issues, as exiting the building in the event of fire would prove difficult.


After all this, they then spent about a week drilling all along the internal dividing wall. Since then the noise we can hear from their house has increased exponentially. They were never particularly quiet (but that was understandable, as they have children), but since the work we can hear conversations, not just noises.

I’m fairly sure they have contravened the planning rules, but I’d appreciate clarification regarding exempted work and the limits on same.

By all accounts your adjoining neighbours have been busy extending and renovating their home over the years, writes Andrew O’Gorman.

Your query is quite complex with a number of site-specific questions raised. Without having the opportunity to carry out a physical site inspection, I will endeavour to answer your queries which relate to planning and development.

The planning process in Ireland is governed by the Planning and Development Acts (and associated regulations). Each local authority is designated as the statutory planning authority for their functional area with responsibility for the operation of the planning process.

The majority of development works require planning permission, however, there are certain exemptions when it comes to works at a private dwelling. These are known as “exempted development”, but particular requirements must be complied with.


A property owner may construct an extension to the rear of their home without having to apply for planning permission.

There are specific parameters one should follow when designing a rear extension for their home:

  • The total floor area of the extension and any previous extensions should not exceed 40sq m (430sq ft).
  • Two square metres of the 40sq m exemption can be incorporated as a first-floor extension (however, the total floor area should still remain below the 40sq m).
  • The design of the extension should not extend forward of the rear line of the existing dwelling.
  • The overall height of any such extension should not exceed the ridge height of the existing dwelling (however, there are some further rules which apply here).
  • Windows can be incorporated in the extension with ground-floor windows having to be at least 1m from a boundary line which they face. Windows at first-floor level should be positioned so they are not less than 11m from the boundary line they face.

Garden shed

Under the planning and development regulations, your neighbours may construct a garden shed in their rear garden without having to apply for planning permission.

The criteria that should be followed to ensure the works are exempt from the requirements of planning permission are as follows:

  • The floor area of any such shed should not exceed 25sq m.
  • The shed should not be positioned forward of the front wall of the existing dwelling.
  • The overall height of the shed should not exceed 4m for a pitched roof and 3m for a flat roofed structure.
  • The shed should not be lived in, and it should not be used for the keeping of animals.

Attic conversion

I am unsure from your query whether your neighbours have provided a habitable room in their attic. From my experience of semidetached attic conversions, the majority of such conversions are not habitable due to the restrictive height of the roof. For this reason, I am basing my comments on a non-habitable attic space.

An attic can be converted for non-habitable purposes without having to apply for planning permission. However, if the works involve the incorporation of dormer roof windows on any elevation, then you are required to apply for planning permission for such a conversion.

Decking area

I am unsure as to the type of structure that comprises the decking area at the end of your neighbours’ garden. However, it is my opinion this structure did not require planning permission provided it is being used for a purpose incidental to the enjoyment of the house and not used for the parking of cars.

Private open space

With regard to your “private open space” query, the presence of the various extensions and garden shed on your neighbours’ property should not reduce their private open space by less than 25sq m (269sq ft). It is my opinion the decking area would be classed as being part of this private open space.

While it would appear your neighbours have undertaken quite an amount of work on their home, it is likely the completed works are in substantial compliance with the requirements of the planning and development regulations.

However, to satisfy your concerns, I recommend you consult your local chartered building surveyor to complete a site-specific survey and assessment.


I note that you now hear your neighbours’ conversations following recent works in their home. It might be helpful to firstly make contact with your neighbour to ascertain if there is a particular issue that has led to such noise transference becoming more pronounced.

There are particular building interventions to assist here and it may be possible to install these on either side of the party wall that separates your homes. The free legal advice service (Flac) has a helpful information leaflet on neighbour disputes (July 2015), which can be accessed online at

Andrew O’Gorman is a chartered building surveyor and member of the Society of Chartered Surveyors Ireland