One of the biggest misconceptions about building a new home is that construction costs are controlled by the builder.

By the time the builder starts construction, however, many of the decisions that determine the cost of your house have already been made.

The size of the house has been decided.

The foundations have been designed.

The structural spans have been established.

The roof shape exists.

The windows have been selected and positioned.

The bathrooms and kitchen are located.

The house has been positioned on the site.

In other words, a very large proportion of your eventual building cost is determined during design—not during construction.

I sometimes describe this as the 80% Rule.

It isn't intended as a precise accounting formula. The point is that the greatest opportunity to influence the final cost of a building occurs surprisingly early in the project.

And this has an important consequence:

If you want to control your building budget, don't wait for the builder's q...

Why Two 200m² Houses Can Cost $200,000 Apart

Two houses are both 200m².

They have the same number of bedrooms, similar bathrooms, a double garage and comparable interior finishes.

Yet one costs $850,000 to build and the other costs more than $1 million.

How can that be?

When people start planning a new home in New Zealand, one of the first questions they often ask is:

“What is the building cost per square metre?”

It sounds like a sensible question. Unfortunately, it can also be very misleading.

After many years designing houses, I have found that the number of square metres is only one part of what determines the final building cost.

The geometry of the house, roof design, structural spans, foundations, glazing, site conditions and even where you position the house on the section can have an enormous effect on cost.

This is also why good architectural design can potentially save considerably more than simply choosing cheaper finishes later.

Let's look at why.

1. A Square Me...