Size, quality and complexity

SizeMeasure from what you know

Size is the biggest of the three. Every square metre has to be built, and then heated, cooled, cleaned and maintained for the life of the house.

Use real rooms as your baseline. A brief that says "a bedroom 4 metres by 6 metres" is a number without a reference. Is that bigger than the bedroom you have now, or smaller? Measure the rooms you live in today. For each one, decide whether the new room needs to be a little bigger, the same, or could be smaller. That's a far more reliable brief than numbers chosen in the abstract, and it often shows that rooms can be smaller than you thought.

Count the rooms and how they connect. The number of rooms matters as much as their size. Every separate room adds walls, doors, light switches and often a corridor to reach it. Corridors are floor area you pay for and only walk through. Let rooms open into each other where it makes sense, combine spaces that are used at different times, and use some open planning to share circulation. A plan with fewer, well-connected rooms is cheaper than one with many small ones.

Add the walls. When people add up the room sizes in their brief, they forget the walls. Internal walls and the outside perimeter add between 10% and 15% to the total. Rooms that add up to 200 m² make a house of about 220 to 230 m². Allow for it from the start, or the house will grow past the budget before it's drawn.

QualityRequirements aren't upgrades

The baseline is the baseline. The insulation, windows and sealing needed to get through approval, meeting the National Construction Code and seven stars, aren't upgrades. They're what's required to build a house at all. Budget for them as part of the house, not as optional extras to trim later.

Watch the allowances. The most common budget shock is the kitchen and the joinery. A brief often carries a single allowance for the kitchen, and built-in joinery ends up everywhere: the study, the laundry, every robe, the living room, the entry. When those items are designed and priced, they regularly come back at double what was hoped or budgeted. Decide early where joinery really earns its place, and get the kitchen designed and priced while the budget can still adjust.

Save by planning for later. Some savings come from what you don't do now:

• Fold rooms into each other. A room that serves two purposes, such as a study that's also a guest room, saves a whole room.
• Install later. Some things can be put in later, or replaced in five or ten years: loose furniture instead of built-in joinery in secondary rooms, floor coverings, light fittings and appliances, and parts of the landscaping.
• Allow for it, but don't install it. Run conduit, rough in the plumbing, put blocking in the walls or set down the slab for something you'll add later. The cost now is small, and the work later is easy.

What can't wait is anything that gets built over: the structure, insulation, windows, waterproofing and anything inside the walls.

And if you can afford to do it all the first time, do. Bringing a builder back later costs about twice as much as doing the same work during the main build, before you count the disruption of living through it.

ComplexityBuild in standard ways

Design for standard construction first. Builders, trades and suppliers are set up for certain ways of building. A house that uses them, with standard framing, standard spans, standard window and door sizes and familiar details, costs less, is built faster and goes wrong less often. Be clever only where it counts.

Beware the beautiful pictures. The images that fill Pinterest and Instagram tend to share the same features: big open expanses with no visible structure, walls of glass that fold or slide away to open a whole room to the garden, and details so clean that nothing seems to join anything. They look effortless. They're among the most expensive things you can ask a builder to do.

The less you see, the more it costs. Construction is a series of layers, each one covering the edge of the last. Skirtings, architraves and cover strips exist to hide the joints between those layers, where one material meets another and where things move. Strip them away, with flush doors, shadow-line joints and floors that run straight into walls, and every junction has to be built precisely enough to be seen. That takes more time, more skill and more expensive materials. A minimal look is rarely the cheap option.

Complexity costs twice. Every corner, roof junction, change of level and large opening adds cost to build it, and usually adds cost to the energy performance too. A simple, compact, well-oriented house can reach seven stars with standard windows and insulation. The more interesting the form, the harder the building envelope has to work, and the more it costs to get there.

The balanceChoosing what matters

With the construction budget fixed, the three levers trade against each other. A larger house means a simpler form or plainer finishes. Better windows and a better kitchen mean a smaller or simpler house. A dramatic form means less floor area or fewer upgrades elsewhere.

There's no wrong answer, only an unconsidered one. The most useful early conversation is about which of the three matters most to you, and which you're happy to hold back on. Made deliberately, against a real number, that choice is what makes a house feel generous on a budget rather than squeezed by it.