Building advice: Taking on a corner site alongside an existing home

What to do when building a new home on the same land of an existing property

Corner sites: Your architect or engineer will need to provide for adequate parking for the new cars for your new home as well as a safe access onto the main road in terms of sightlines. File Picture.

Hi Kieran,

My partner and I have recently moved back to Cork from Dublin. We are both lucky enough to relocate and we are both currently renting. With house prices moving up at the moment we had a bit of a brainwave to get a place of our own. My Mom is a widow and she has a large extended semi-detached house on a corner site in the south side of the city. The house is too big for her and she is happy to look at options so that we all have our own living space. I am wondering what we need to consider in terms of road access. Because there will be two separate houses, is there anything else I need to consider? We believe that if this works well, we will get the house we want in the location we want as well.Regards, Finbar

Hello Finbar, and thank you for your question. 

You are indeed in a fortunate position and it would be wonderful to be able to get this project to work for you, especially considering the huge lack of supply of good quality living accommodation in Cork and indeed throughout the country, not to mention the recent escalation of housing prices. So what items do you need to bear in mind?

Let’s start with planning permission. I am assuming that, given the fact that your mother is living on a corner site that you are considering extending to the side and that you will be providing your own front entrance. In this instance you will need to apply for planning permission.

Here you need to ensure that you retain adequate separation distances from neighbouring properties in terms of boundaries and first-floor window sightlines.

Kieran McCarthy: 'I always recommend a neighbourly discussion whereby you take any of their comments on board to maintain good relations and to help ease your new design through the planning process.'

During this planning process, your architect or engineer will need to provide for adequate parking for the new cars for your new home as well as a safe access onto the main road in terms of sightlines. It is highly likely that the new house will need to be built in the same style format as the existing house as it is an infill type development.

Given that you are likely seeking planning permission in a built up area, perhaps even the area you grew up in and that you propose to carry out a significant building project, once you have plans in place I would begin speaking with your neighbours.

They may be affected by your proposed new house design and that you protect their access to light and privacy in your new design. I always recommend a neighbourly discussion whereby you take any of their comments on board to maintain good relations and to help ease your new design through the planning process.

Given that your mother’s house is too big, it might be worth considering taking possession of this dwelling and building a more modest unit to the side for your mother?

Now that you are renovating a substantial house, the new NZeb building regulations dictate that once you are upgrading more that 25% of the external envelope of this house, you will need to bring the entire house up to a B2 BER Rating. Though this is quite onerous, there is a huge long term value in making your new home more energy efficient.

If your mother’s house is quite old there are considerable deep retrofit grants available nowadays and well worth checking out. If you have the budget I would ideally advise taking it a step further and fitting an air-to-water heating system, demand control ventilation and perhaps external insulation.

These measures, coupled with a good level of Airtightness, A-Rated windows and attic insulation would likely take you into an A Rating. Yes, it’s a significant initial investment but you end up with a very efficient and comfortable home.

I would consider the long term plan here also. As time wears on it is likely that indeed your family may inherit your mum’s new house. In this case, would you sell it or would you seek to amalgamate it into your house by way of a side extension? If this is indeed the case then I would consider how this would work in terms of hallway access etc to ensure it doesn’t cause major disruption later on.

Finally, I would consider what this area would be like to raise a young family. It may be that you and your partner are looking for a roof over your head for now but we all know that circumstances change and that in time you may be rearing children in this house and indeed neighbourhood.

Is there access to good schools and parks? Are there sports clubs or indeed a community hall nearby? Is there a bus route into town? Are there other young couples or families relocating to this area? What is the community like? These are all long-term key factors to consider as you look to a bright future in your new family home.

• Civil engineer Kieran McCarthy is founder, and design and build director with KMC Homes. He is a co-presenter of the RTÉ show Cheap Irish Houses.