How many square metres do I need to build a house?

One of the first questions a family faces when building a house is: how many square metres do I need to build a house?

First of all, it is essential to start by analysing our current and future lifestyle. In our sustainable architecture studio in Barcelona, most of our clients are young couples with children or planning to have them soon, but also families with teenage or university-age children, or retirees who want to redistribute unused spaces.

Every family is different, and each stage they go through requires addressing different needs. Children can share a bedroom when they are young, but later they usually want their own space. Then, when they move out, rooms are left empty, which may be excessive for parents or very useful for visiting friends and family.

For this reason, the square metres we need will depend on our current and future needs, but we also need to consider how our family may evolve and what needs will arise at each stage.

Designing a home for two people

When considering how many square metres you need to build a house, it is a good idea to start by assessing how many square metres a home for two people requires. How many square metres, at a minimum, do my partner and I need to live?

Spanish regulations establish that the minimum habitable area is 30 m², but if we are talking about how many square metres we need to build a house, we should, at a minimum, plan for an area starting from 60–70 m².

From there, we can distribute the space into one bedroom, one bathroom, and a kitchen and living room, which will serve as an initial base, with the option to add more square metres as our needs evolve.

We always recommend taking the Mediterranean climate our country enjoys into account and making the most of it by creating semi-covered outdoor spaces with pergolas or porches—sunny in winter and cool in summer—which allow us to extend the home’s usable area outdoors at minimal cost.

Building a pergola, for example, is a minimal investment and can allow us to double the surface area of our living room for many months of the year.

Another recommendation is to “think small” or follow the principle of “less is more”.

A small house has lower maintenance costs and is easier to heat, clean, and maintain.

If we are considering an eco-friendly home, it is easier to achieve higher energy efficiency when spaces are smaller; for this, a small house with controlled spaces will be far more efficient.

There is always time to add more square metres in the future or to use resources such as outdoor porches to increase the usable area.

A final recommendation is to include an additional guest WC for visitors, especially in a home with only one bathroom, as it allows you to keep the more private areas of your home reserved.

Based on all these criteria, the standard for a couple of two who occasionally hosts guests and wants to live comfortably would be between 80 and 150 m², bearing in mind that this would be expanded with outdoor porch spaces.

Designing a home for 4 people

Let us now move on to the second case: a home for a family of four.

When a project for a family of four comes to our studio, we analyse the family’s current and future situation.

Essentially, the key is to know the children’s ages in order to assess their needs.

As for the number of bedrooms, this is a very personal decision for each family.

Teenagers undoubtedly want their own space, but some families prefer children to sleep separately from a young age, while others prefer to keep them in a single bedroom until adolescence.

In any case, it is necessary to plan for extra rooms that for a few years can serve as playrooms or study rooms and that can be connected to living areas, to later become independent bedrooms.

Again, if we are considering the construction of a house, the recommended minimum in this case would be two full bathrooms with a shower or bathtub, one of which can serve as a guest bathroom and the other be more private for family use, or even be within the main bedroom.

In summary, the minimum complete programme would be: 3 bedrooms (one double) and two children’s bedrooms, one of which could be flexible for use as a bedroom, playroom, or study, 2 full bathrooms, a kitchen, and a living room.

Here, the minimum square metres will increase to approximately 100 m², taking into account the recommendations from the previous point:

– “Less is more”

– Include porch spaces wherever possible

The standard size for a home with these characteristics would be around 150 m², and the size of a comfortable and flexible home would be around 200–250 m², although here again it is worth asking what happens to the extra square metres when the children move out.