Build a new home or renovate an old property? 

Kieran McCarthy offers his expert view on what to consider when deciding to either build or renovate 

A renovated bungalow will have some connection to the original house, though with the caveat that you will be a little restricted in your new design by the original structure. This was a new/replacement build and a Home of the Year finalist in 2018

Hi Kieran, 

My wife and I have recently inherited one and one-third properties: an old farmhouse we fully own, and a 1970s bungalow, approximately 1,300 sq ft, which my two sisters and I now own between us. 

My wife and I are exploring the possibility of purchasing the bungalow outright and renovating the bungalow instead of going ahead with a new 2,500 sq ft build on the site of the farmhouse. Our initial idea is to renovate and convert the bungalow into a 1.5-storey house, aligning it with the architectural style of newer houses in the area. 

The main advantage of the bungalow is its proximity to Nenagh (2km) compared to the farmhouse (10km). How financially feasible would the renovation be compared to the 2,500 ft new build? Your insights would be greatly appreciated as we navigate this decision-making process.

Best regards, 

David and Aine, Nenagh. 

Hello David and Aine, 

Thank you for your question. What a very fortunate position you find yourself in.

So you essentially have a choice of two very different projects to carry out which will result in two very different ‘new’ homes in two different parts of the county, and for two different building costs but which one is right for you?

To be honest, I don’t know because I don’t know you well enough to advise you but I can outline what I do know, which is what the two projects would broadly entail and hopefully that will help you with your final choice so let’s compare.

Regarding the 1970s bungalow, these bungalows are generally quite simple to renovate if you are maintaining the current footprint (as they normally have a 100mm cavity between the two leaves of blockwork making it quite simple and cost-effective to insulate).

Top to bottom

However, in your case, you are looking to add a first-floor dormer roof to this bungalow to make it 1.5 storeys. I feel that if you are doing this you will need a full new render system externally to ensure a consistent finish from top to bottom.

Because of the size of your renovation project, I feel you will need to bring your whole house up to the new NZeb (Nearly Zero-Emission) building regulations, which broadly means your finished house needs to reach a B2 BER or better. With this in mind, I would probably externally insulate the entire house giving you a new and very well-insulated external facade.

Finished homes need to reach B2 Ber or better to bring it to the new NZeb (Nearly Zero-Emission) building regulations

The next big ticket item to be considered is the ground floor slab. This will currently have a minimal amount of insulation underneath so I would look to remove this and replace it with a new slab with 150mm rigid insulation and a radon membrane and sumps underneath. At this level of retrofit, it would well be worth considering a new efficient heating system such as an air-to-water system which could contain an underfloor heating element in your new slab build-up.

So, now you have designed the new ground floor slab and the external frame, the next element to consider is your dormer roof. In this structure, you will likely have sloped and flat ceilings. The sloped ceilings will need to be insulated with rigid insulation between the rafters (leaving a gap for ventilation under the roofing felt) and an insulated plasterboard slab underneath (to guard against cold bridging). The other key element required here would be an air-tightness membrane (as I am assuming you will be likely to install a ventilation system).

The factors involved

Now that we have the entire frame designed, let’s look at what other elements need to be considered. Firstly, there is a lot of labour-intensive demolition (walls in the existing ground floor to suit new layouts, existing roof in entirety, existing ground floor slab, existing ground floor finishes, existing drains if clay). There will be structural steel needed to facilitate new open-plan layouts and there will be an entire new first floor and roof structure and finishes. 

There will be a complete new windows package, a new electrical, heating, plumbing, and ventilation system. The new finished house will be entirely rendered externally and likely skimmed internally and, of course, there will be a complete suite of finishes fitted including, kitchen, utility, built-ins, stairs, carpentry, bathrooms, floors, painting, and so on. So, all you really get to keep from the old house are a series of ground floor walls (assuming they are structurally sound and there was no subsidence present). But what about plan B?

Demolishing a home carries a major price tag, on top of removing it to a landfill site

To build the new house, you will need to demolish the existing house on the site (a not insignificant cost in itself) and remove it to a licensed landfill site. You will then need to build an entirely new A2-rated house (to comply with building regulations) on this site and allow for all new service connections and so on. This is by no means a small body of work but much simpler to define than the demolitions, renovations, and rebuild in plan A, the bungalow renovation.

Decision time

So which is best? I feel the new build could well be quicker and it’s much simpler and more predictable. You will also get much more interest from local builders for a new build project so I feel you will get better value when building. It will be simpler to budget for as your biggest area of risk is in the ground and you don’t have to worry about the condition of the existing building you are working with.

Kieran McCarthy, KMC Homes, engineer and builder.Picture Denis Minihane.

I also feel there won’t be a massive price difference between the two projects though the new build may cost a little more. Both houses when complete will look and feel new and have similar energy ratings.

Not much difference then in terms of project time, cost, and end product, so what will determine which works best for you?

The renovated bungalow will have some connection to the original house, though with the caveat that you will be a little restricted in your new design by the original structure. Maybe this connection to the past is important to you. Maybe the shorter commute to Nenagh dramatically improves daily life. Maybe the idea of demolishing the old farmhouse in Plan B is a step too far.

I don’t know, but, don’t forget, all things being equal above (or nearly) you will still have a big bill to settle with your sisters if you opt for plan A.

• Kieran McCarthy is a building engineer and director of KMC Homes bespoke A-rated new home builder, serving Cork and Limerick. He is also a co-presenter of the RTÉ property show Cheap Irish Homes.

• Follow Kieran on Instagram @kierankmc for more home-building information, tips and Q&A advice.

• You can also follow Kieran on the Built Around You Youtube channel and @kierankmc on TikTok. Readers are invited to send their home build queries to [e-mail].