Before building a house, almost everyone has the same question: roughly how much will it cost? The answer is rarely a single figure. A house is made up of many jobs, and some of the biggest costs sit in parts you won’t see once it is finished, such as the foundations.

This guide is for anyone who already has land, or is weighing up a plot, and wants to estimate the cost of building before calling in a contractor. It covers two ways to calculate, the cost components, and the costs outside the building that people often forget.

The figures in this article are illustrative only, to show the method. Material prices and wages differ by area and change over time.

Two ways to calculate: per square metre and a RAB

The first way is a per square metre estimate. You multiply the floor area by a rate per m² from a local contractor or builder for a given specification. It is quick and useful early on, for example to decide whether your budget covers one storey or two.

The weakness is that a per m² rate hides a lot. Always ask what it includes: foundations suited to the ground at your site, the fence, the carport, electrics and plumbing, and how porches and carports are counted.

The second way is a RAB (Rencana Anggaran Biaya, a detailed cost plan). A RAB lists every job, from excavation to painting, with its quantity and unit price. Because it is based on working drawings, its figures are far more dependable. It also becomes your tool for comparing quotes and controlling spending during the build.

Use the per m² estimate to set a direction, then the RAB to set the budget.

What goes into the building cost

In a RAB for a house, the work is usually grouped like this:

  • Preparation, such as clearing the site, setting out, a materials store and temporary power.
  • Earthworks and foundations, including excavation, fill and the foundations themselves.
  • Structure, meaning ground beams, columns, beams and floor slabs if the house has upper storeys.
  • Walls, in brick or another material, then rendering and skim coat.
  • Roof, meaning the frame, the roof covering and gutters.
  • Frames, doors and windows, in timber, aluminium or another material.
  • Floors and ceilings, including tiles and ceiling frames.
  • Electrics, clean water and drainage, including the septic tank.
  • Painting and finishes, where budgets can easily swell because there are so many choices.

Costs outside the building that people forget

A per m² rate or a RAB for the building often leaves out these:

  • Design and working drawings from an architect or draughtsperson.
  • The PBG (Persetujuan Bangunan Gedung, the building approval), with fees set by each local regulation. The process is explained in our guide to the PBG.
  • Power and water connections. A new connection from PLN (the state electricity company) needs an SLO (Sertifikat Laik Operasi, the certificate that the wiring is safe to connect), and a connection to the PDAM (the regional water utility) has its own cost.
  • Fill, if the plot sits below the road.
  • The fence, carport and perimeter drains.
  • Supervision, if you hire a supervisor or an architect to watch the work.
  • Furniture and appliances you need to move in.

Then add a contingency of 10 to 15 percent of the construction cost. It covers unexpected work, rising material prices and small changes during the build.

Soft ground and soil testing

Much of South Kalimantan’s lowland is swamp or peat, especially around Banjarmasin. On ground like this, the foundations can take a much bigger share of the budget than on firm soil.

Options used locally include cerucuk (driven piles of galam timber), concrete piles and cakar ayam, an Indonesian foundation system for soft soil. The right one depends on the building’s load and the ground beneath it.

So don’t skip the soil investigation. An uji sondir (a cone penetration test) measures how much load the ground can bear at several points, and the results are used to design the foundations. It usually costs far less than repairing a house that has sunk or cracked. If the plot has been filled, read buying filled land as well.

The specification decides the final figure

Two houses of the same size can cost very different amounts because of their specification. The specification is the list of materials and grades: the type of tiles, roof frame and covering, door and window frames, sanitaryware, and so on.

A few things have a big effect:

  • Timber. Ulin (Bornean ironwood) is very durable but expensive. Use it where it matters most, such as near the ground or water, and other materials where the timber is sheltered.
  • Number of storeys. A two-storey house needs a stronger structure and a staircase, but it uses less land.
  • Floor plan shape. A plan with many corners and recesses needs more wall and more roof work.
  • Finishes. Floors, sanitaryware and frames can differ several times over in price for the same function.

Write the specification before you ask for quotes. Without it, two quotes can’t be compared.

A simple worked example

Worked example (illustrative numbers only, not prices in any area):

  • A single-storey house of 90 m², mid-range specification, at a rate of, say, Rp 4 million per m² excluding special foundations: Rp 360 million.
  • Extra foundations for soft ground, say Rp 45 million.
  • Fence, carport and drains, say Rp 35 million.
  • Construction cost: Rp 440 million.
  • Contingency at 12 percent of the construction cost: about Rp 53 million.
  • Design, PBG, and power and water connections, say Rp 20 million.
  • Estimated total: about Rp 513 million.

Notice that the total is roughly 40 percent above the first sum of 90 m² times the per m² rate. A gap like that is how budgets blow out when people rely on the per m² rate alone.

Building in stages and comparing quotes

If the money isn’t there yet, building in stages can be a middle path. For example, the structure and roof go up first and the finishes follow. Or the house is built as one storey first, with foundations and columns already designed for a second.

Keep two things in mind. Plan the next stage from the start, because strengthening foundations later is much harder. And count the cost of restarting, since builders and equipment have to come back and prices may have risen.

For quotes, get at least three based on the same drawings and specification. Compare them job by job rather than by the total alone. A quote far below the others usually means some work hasn’t been priced or the materials have been downgraded. Choosing who builds it is covered in choosing a contractor.

Next steps

  1. Decide the rooms you need and a rough floor area.
  2. Ask two or three local builders for a per m² rate as a first guide.
  3. Get a soil test done and the working drawings prepared.
  4. Draw up the RAB and the specification, then ask for comparable quotes.
  5. Add the costs outside the building and a contingency before you decide.

If you need a detailed design and RAB, Vorneo has a partnership with a design and build studio in South Kalimantan.