Kieran McCarthy: Making sure you get the foundations of your home build right

The ground floor slab is one of the biggest milestones on your project. Picture:iStock

Hello Kieran, 

My builder is laying the foundations of my house today. What is the next thing for me to research, decide, or get a quote for? 

Thank you, 

Ruth, Waterford

Hello Ruth,

This is indeed a great question and quite unlike the usual questions I get which is exciting. In my day job I run a design and build company and as such, outside of our responsibility to build a new home for our clients, we also have to bring them along on the journey with us as smoothly and efficiently as possible.

They are, of course, busy with their own home and professional lives so there is a very limited amount of time and energy they have available for their new build so we have to get it right first time. So, where to start?

You mention that you have a builder on board so I am assuming that you have a main contractor and that he/she will have all the key trades in place (blocklayers, roofers, plasterers, etc) so what responsibilities rest on you are the client choice items (or selections as we call them).

At the stage of having poured your footings the next big stage will be pouring your ground floor slab. This may sound like a simple stage but in truth it is one of the biggest milestones on your project so let’s start here. In this slab, much of your plumbing and indeed heating choice and locations are now set in stone (literally).

Kieran McCarthy: 'Much of your plumbing and indeed heating choice and locations are now set in stone (literally)'

In most new builds now, the ground floor slab or screed will contain the underfloor heating for your entire ground floor. This means you don’t have to worry about where your radiators are located but you do need to look out for any areas where you don’t want underfloor heating. Yes, you read correctly; you don’t want your warm slab heating your food cupboards or pantry so you tend to avoid placing the heating pipes in these locations. A broad kitchen plan from your kitchen supplier will be sufficient here. Another consideration is that if you cannot drill and fix screws down though underfloor heating (for obvious reasons) so you will need to ensure follow-on trades are aware of this (eg, your stairs installer).

As part of this underfloor heating system you will need one if not two heating manifolds (pipe junction areas) to find low profile locations for (closets or utility rooms are ideal).

Next comes the plumbing. All the bathrooms on the ground floor will need to be signed-off in terms of the location of your toilet bowl, sink and shower though there is some wriggle-room in terms of final bathroom ware choice. If you are keen to avoid external vertical sewer pipes (soil vent pipes) then you need to speak to your builder and find a route from your upstairs toilet to your ground floor sewer. Again this facility needs to be designed-in before the concrete is poured. Some builders will be ahead of you on this but some builders prefer to locate this externally for access in case of maintenance so best to liaise with your builder to see what they prefer.

Speaking of plumbing, how are your kitchen plans progressing? Ideally at this stage you will be signing-off on your kitchen company choice and beginning to converge on a kitchen plan. This does not need to be 100% perfect but I would certainly try to get it to 75% so you are broadly happy with the placement of all the key elements.

Of utmost importance here is what is going in your island if you are having one. Hob or sink? Is your hob electric induction, gas, or hybrid (electric and gas)? You cannot change this afterwards as you will not be able to put in the necessary plumbing due to the fact that your concrete is poured containing your underfloor heating. I have also noticed that there are some extraction units now that require the ventilation duct to be run underground so best to explore these options with your kitchen company. It should again be mentioned however that you have some room for error if you want to make some final adjustments as you converge on the last 25% of your kitchen design as much of the plumbing and electrics get placed behind your cupboards so they can be easily tweaked, out of sight. Your kitchen company will advise the plumber and electrician of these final service layouts when the plans are complete.

Of utmost importance in the kitchen is what is going in your island if you are having one.

A final consideration is any other adjustments that may be required in the slab itself with respect to follow-on finishes. Are you installing different flooring of different thicknesses? If there is a substantial difference in thickness (eg, polished concrete v glued semi-solid herringbone timber) then best to adjust the levels of your concrete slab locally to accommodate. Another feature some people like to install is matwells in hallways. These can be very handy where young children or outdoor pursuits are involved as they allow for a deep robust mat to be installed at the first point of entry.

Ruth, you may at this stage be regretting having asked me this question as it may feel that you have your Leaving Cert coming in four weeks and you have very little revision done but trust me, if you hit the ground running now with your plumber and your kitchen company you will work out the broad strokes quicker than you think and you will be well ahead of your builder for the near future, well, at least until he asks “have your windows chosen yet?”.

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

Follow Kieran on Instagram https://www.instagram.com/kierankmc for more home-building information, tips and Q&A advice.

Tune in to Kieran’s new podcast, Built Around You on Apple Podcasts and Spotify and on the Built Around You Youtube channel