Kieran McCarthy: Does your home's design affect building costs?

This is an excellent question, and it brings to the surface many key design and budget considerations that may not be apparent at the start

Your living space will ideally be orientated with an amount of southerly aspect so you capture the sun for as much of the day as possible.

Hi Kieran 

My partner and I are building our new forever home on our site in the countryside. Is there much of a saving in building a rectangular shape as opposed to an L, T or U?

Jean, Co Meath 

Hi Jean, 

This is indeed an excellent question, and it brings to the surface many key design and budget considerations, some of which may not be apparent just yet, but let's take this opportunity to dive into these and work through them.

In the past, houses were designed from the outside in. Most Irish traditional stone cottages have a similar shape and footprint (take it from me!), and most Georgian houses are largely rectangular or almost square in shape. 

The advent of the 20th century saw masonry graduate to blockwork and the advent of the bungalow and the three-bed semi-detached house. The external shape remained fixed, and the resulting internal area defined your internal space and access to daylight.

In the past, when houses were largely for shelter and warmth, this approach worked fine, but since then our lives have changed considerably, and we now have much more leisure time, greater insulation and heating systems, our expectations have changed. 

We need our homes to provide shelter, warmth and security, but also offer space for relaxation, entertainment and a peaceful and enriching home life.

If you have a reasonable budget available, then best to invest in design that optimises for light.

Nowadays, houses are ideally designed the other way round. An architect will look at the path of the sun, views to be captured, internal space and lifestyle requirements, planning policy, site characteristics and essentially design the house around these, from the inside out. 

Firstly, you need to look at the path of the sun, because that is the most important consideration. Your living space will ideally be orientated with an amount of southerly aspect so you capture the sun for as much of the day as possible. 

South-east for morning light, right through to south west for later in the afternoon. With your living space sited, this maps your patio externally, your utility room is probably nearby, but opening onto a lower profile external elevation. 

Your second sitting room/study is probably facing the same direction as the majority of your living space (for the same reason), and now most of the rest of your ground floor footprint is lower-profile space in terms of light, so perfect for your hallway, cloak room, WC and front door. 

This may mean your front door is not actually facing the road as it generally did in the past. The aim here is to orientate your house to daylight first, and everything else clicks in afterwards.

This is the best way to design a house from an architectural point of view, but is it the most cost-effective? Probably not, because it may mean introducing certain shapes of floor plan to optimally capture the daylight available and perhaps to provide shelter from wind. 

Whenever you break from the most cost-effective house shape (a rectangle), you add cost. This is what quantity surveyors call the "wall to floor ratio". 

This is the ratio of external walls to floor area. The greater the external walls here, the more expensive your home will cost to build per square foot. So, should you just stick with a rectangle? Let's see.

If you have absolutely no choice in terms of your available budget, then a rectangular house is likely the best shape for you, all things considered. When it comes to considering an L, T or U-shaped house, again I think you may be looking at the wrong end of the stick. 

I have designed efficient Ls and Ts, but in the context of designing from the inside out, not the other way around. Whereas a U-shaped house may look great, it will push your budget further.

If, however, you have a reasonable budget available, then best to invest in design that optimises for light. An approach I have used in this context is to have most of your house in a rectangular shape and allow a little of your budget for an architectural flourish around your living space, where you will spend most of your time at home.

Kieran McCarthy. Picture: Denis Minihane

• 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. Check out KMC Homes’ new website kmchomes.ie 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