Building Advice: Extending a terrace home

What you need to consider when building to the rear and staying on good terms with your neighbours

From a building perspective, the most difficult aspects are drainage, building/weathering to neighbouring properties, and of course access. File Picture

Hi Kieran, I own a small terraced home in Cork City that I would love to completely overhaul and extend out into the back. From a builder’s perspective, what are the challenges that I will face when it comes to extending out the back and avoiding any impact to my neighbours on either side? There is no access to the rear. I want to extend the kitchen into the garden just leaving a small patio at the rear? Any advice is appreciated.

Peter, Cork

Hello Peter and thank you for your question.

Yours is undoubtedly a predicament in which many people find themselves. I too have lived in a mid-terraced house and needed to extend into the rear garden, so I am acutely aware of what you need to consider.

First of all is of course the design. It appears that you are looking to extend your kitchen.

I would advise you to also consider a space for a laundry area (ours ended up in the centre of the house as it was low-profile space). What you are weighing up here is how to create a practical utility space while saving as much light-filled space connecting to your new patio as possible for your new kitchen/living space. It is a delicate but important consideration.

From a planning perspective, you can build up to 40m2 on to the rear of your house, but you need to ensure you leave over 25m2 remaining in your garden. The 40m2 is quite a generous extension allowance and will likely be more than sufficient for your requirements.

Kieran McCarthy: 'Your neighbours are key to the success of your home extension and renovation project.'

From a building perspective, the most difficult aspects are drainage, building/weathering to neighbouring properties, and of course access. Let’s discuss these in turn.

Drainage broadly consists of two elements, storm and foul. Storm drainage is rainwater run-off from your roofs and paving. In most cases, the rainwater is discharged to a soakaway (a large trench in your garden filled with drainage stone and geotextile lining). Cork City Council will likely have a preference for you to deal with your own stormwater in this capacity.

Foul drainage consists of the effluent from your toilets and the greywater from your sinks and washing machines if you don’t separate these. This effluent will need to discharge to the main public sewer.

In most cases (but check before you begin building) this sewer will be out the front of your house, so you will likely need to route your new sewer through your hallway and out the front door. This is a big, disruptive job, but it means that in your finished home you have a new PVC sewer (not clay), which will help avoid any foundation structural problems down the road.

Your new extension is likely to have an interface with either neighbouring boundary walls or neighbouring properties. How your new build finishes meet these existing structures is crucial.

How are they weathered, how are they insulated, and how are they maintained?

Much of this needs to be considered in discussion with your neighbours. Without doubt, this is a joint discussion and agreement. If they were considering an extension, you would hope that they would discuss their plans with you — it’s what good neighbours do.

Another key consideration is how your foundations would work.

In traditional footing-type foundations, the footing protrudes underground beyond the lines of your new walls, although this may not be practical in a confined garden space.

You could speak to your engineer about using a raft foundation which, although a little more expensive, allows you to build on the edge of the raft.

Finally, we come to access. I fondly remember the daily grind of bringing materials through my house as we built the extension. In the beginning, as you dig your foundations and knock walls, you are bringing out soil and debris through the house in a wheelbarrow, then you are barrowing back in cubic metres of concrete through the house.

Next, of course, you need to consider the new walls.

When I was in your situation, we decided to use a timber frame construction to make it easier to bring in the materials needed instead of having to bring in a few thousand concrete blocks by hand.

In timber frame building, you can apply lightweight material to clad the timber frame, both internally and externally, and it could very well make things simpler and quicker.

The downside of timber frame building is that, when you begin to fix the frame back to the old house, you may very well discover, to your surprise, how out of plumb your existing rear walls actually are. This is where good tradesmen come in.

All in all, the biggest consideration is your neighbours. Whether discussing access, planning permission (if required) or boundary/weather/drainage elements, clear and regular communication is key.

Your neighbours are key to the success of your home extension and renovation project — and, ultimately, to your enjoyment of your new home and neighbourhood thereafter.

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.