We want to split our house into two units. Can you give us a ballpark cost?

The plan is to split the deeds of our house and develop it into two units, but this has not been done in the area that I'm aware of. It is a 1,700sq ft three-bedroom semi, with a main bathroom and an attic conversion to a fourth bedroom with en suite. The entrance hall has two rooms to the right and the garage to the left, with a toilet under the stairs. The kitchen and a large family living and dining room, 30ft by 15ft, are at the back of the house. Could you give me any advice regarding an architect coming to look with ideas, and a ballpark cost?

The idea of splitting a large house into smaller units is not new thinking. Most of us have lived in a flat at one time or another, usually in an older property subdivided into small basic units.

It has been long recognised that there is great opportunity for providing homes for many in properties that by their nature are oversized to accommodate normal modern family life.

The potential to subdivide property will usually be facilitated and supported by your local authority.

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Two relevant government policy documents are Rebuilding Ireland – Action Plan for Housing and Homelessness and the very useful 2018 publication Bringing Back Homes, which provides a practical manual for the reuse of existing buildings. Through well-worked and illustrated examples the manual shows how buildings can be subdivided and sets out the various stages involved in the process.

The planning system, exempt development, regulations effecting older buildings, the building control system, minimum standards for rented housing, health and safety and the Fire Services Act are all dealt with. The manual is an ideal starting point when planning to reuse a property or increase the number of viable residential units. The manual can be downloaded free from the Department of Housing, Planning and Local Governments’ website.

In your case you describe a very typical three bed semi-detached house with a converted attic. The most obvious solution here is to split the property horizontally. The upper floor and attic forming one unit with the ground floor forming the other. There may also be potential to develop over the garage.

The alterations would be significant and would need planning permission. The works would necessitate both horizontal and vertical separation between the units to provide a separate ground floor entrance for the upper unit. This separation would need to be designed and built to resist the spread of both sound and fire between the units. Splitting of services in terms of supply and also disposal of waste can also present a challenge.

You will need the help of an experienced architect or building surveyor to help you through the design, planning and building control systems, including a fire safety certificate application. With careful thought however two good quality units could be delivered based on the size of the property you describe.

Costs associated with this type of work will be higher than typical building costs. This is partly because of the requirement to meet modern building regulations and partly because refurbishment costs are usually higher than new build. The work needed to split out services installations can be costly. Usually insulation will need to be improved and windows and doors replaced. You should first establish a realistic budget and then tailor your designs accordingly.

Talk to your local chartered building surveyor or architect. A good designer with an eye for cost control will be key in bringing your plans to fruition.

Noel Larkin is a chartered building surveyor and a member of the Society of Chartered Surveyors Ireland; scsi.ie