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Architect's clinic: Should I convert my garage into a flat for my son?


Making a whole new apartment within the limitations of an existing garage will be challenging. Photo: Getty Images

Making a whole new apartment within the limitations of an existing garage will be challenging. Photo: Getty Images

Getty Images

Making a whole new apartment within the limitations of an existing garage will be challenging. Photo: Getty Images

Q I'm living in a semi-detached house with a garage under the roof of the house. I'm considering converting the entire garage, which runs the depth of the house, into an apartment for my son. The question is: after my death, could the house be sold separately to the apartment? The rest of the house would certainly be big enough. There are four bedrooms, sitting and living rooms and a kitchen, but there would be no side entrance. The new owners would also have a small back garden. What do you think?

AMany homeowners in Ireland consider splitting the plot of an existing property to create two dwellings, one old and one new. Numerous factors influence this kind of development, so for the successful extension and conversion of your garage into a new apartment you might need the stars to align.

Where to start

Perhaps, the best starting point when contemplating this kind of project would be to take a critical look at the architectural design of the garage you would like to convert. A garage is typically '… a building for housing a motor vehicle', so those attached to semi-detached houses have often been designed with internal dimensions to suit cars and built with thin concrete floors at the same level as drives in front of them.

Garages, compared to other rooms in semi-detached houses, are usually narrow, long and unsuitable for human habitation without significant modification. Having said that, there are countless garage conversions attached to houses around Ireland; but while such conversions may add welcome space for the likes of playrooms, utility rooms or WCs, making a whole new apartment within the limitations of an existing garage will be far more challenging, even if it is extended to the rear as you mention. For this reason, it would be prudent to invite a registered architect to visit, look at the garage and advise about its potential to deliver the kind of outcome you desire.

The planning process

Planning regulations allow an existing garage attached to the side of a house to be converted as exempted development to extend the house - subject to relevant limitations such as the permitted total cumulative floor area of extensions and conversions. But the same exemption does not hold true for the creation of a new apartment that you intend to be sold separately from the main house at a future date.

Planning permission will be required for the creation of a new dwelling and, before deciding about an application for development like this, the local planning authority will weigh up a range of factors, starting with relevant policies and objectives in its development plan. These policies will probably seek to balance demand for housing with quality of accommodation and, when evaluating the latter, the planning authority will take into account the likes of local context and precedent; the proposed sizes of the two sites and their respective amenity; vehicle access to the two dwellings; and public services like water supply, drainage and utilities, amongst others.

If you proceed and make a planning application, then you should bear in mind that neighbouring householders may choose to submit observations to the planning authority about the proposal when the planning process is underway. Furthermore, you should bear in mind that if permission is granted it could - potentially - be accompanied by conditions limiting the occupancy of the new dwelling to family members such as your son.

Building Regs and Commencement Notice

When planning permission is granted, then a Commencement Notice must be submitted before any building work can start, the purpose of which is to notify the local building control authority of your intention to carry out building work.

All building work associated with both the creation of the new apartment and the material alteration of your main house will be needed to satisfy the Building Regulations; and while you may have the choice to opt out of full BC(A)R requirements, some obligations in this respect will still apply. Aside from these, BER assessments will also be required.

Site safety

Depending on the design of the new apartment and its interface with the main house, you will be faced with deciding whether you will continue living in the house while building work is being carried out. Builders generally prefer to carry out work on vacant, rather than occupied properties, for several reasons including efficiency, site security and safety. You should consider the latter, in particular, when making a decision to stay or go, and your architect will be able to advise you.


Another aspect deserving careful consideration is cost. If planning permission for a new dwelling is granted, you can expect to pay a development contribution calculated on a square metre rate and payable to the local planning authority.

The building work to extend and convert the old garage into an apartment will entail its own costs. On top of that, there will be fees for building design professionals like an architect, a BER assessor and also a solicitor when the new property is registered with the Property Registration Authority.

If you intend to sell the apartment separately from the house at a later date, then it would be worth checking with an experienced auctioneer how the expected future sale value of the two properties might compare to your initial investment and, furthermore, if any tax liability could arise at the time of sale.


It would be prudent to take all these factors into account when deciding if converting your garage into an apartment is going to deliver the outcome you desire.

You might wish to explore the alternative of sub-dividing the whole four-bedroom house in other ways to create an apartment for your son and a second property with the potential to be sold separately. If such alternatives are of interest to you, then a good point of reference would be the Abhaile project (avahousing.ie), winner of the 'Rebuilding Ireland: Homes for Smart Ageing' in 2017.

If you are considering changes to your home, work with a registered architect. Find one on riai.ie, the registration body for architects in Ireland.

Architect Mark Costello is a member of RIAI, and can be found at strandarchitects.eu

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