The net-zero house starter kit: retrofitting Indonesia's Type 36 home
Why the cheapest, most-built house in Indonesia is the right place to start a net-zero conversation — a short summary of my final degree project.
Most net-zero building research aims high — bespoke homes, premium envelopes, budgets the mass market will never reach. My final degree project at Kyushu University goes the other way: to the Type 36, the 36 m² "starter home" mass-produced by the thousand across Indonesia.
The thermal oven
A standard Type 36 is built from uninsulated batako concrete-block walls and a thin zinc roof. In Jakarta's 29–31 °C climate, that envelope behaves like an oven: the roof radiates solar heat straight into the living space, and the walls store heat all day and release it all night. Households fight back with air conditioning set as low as 20 °C — pushing annual bills past IDR 15 million on a grid that is still around 61% coal.
A "Cooling Survival Kit"
Instead of rebuilding the house, I tested a low-cost retrofit on the existing stock, simulated in Energy3D against Jakarta weather data:
- Roof insulation — glass wool, bringing the roof U-value down to 0.5 W/m²K
- Shading — window overhangs and trees
- Inverter AC — COP 4.0 instead of 2.8
- A behavioural nudge — raising the setpoint from 20 °C to 22 °C
The result
The combined kit cut simulated annual electricity use by ~57% — from 10,553 kWh to 4,521 kWh.
That drops annual energy cost from ~IDR 15.2M to ~IDR 6.5M. The inverter upgrade alone pays for itself in about three months; the full kit reaches a simple payback of roughly five years on measures that last decades.
Why it matters
Indonesia's "One Million Houses" program prioritises quantity over thermal performance, locking millions of new households into decades of high energy dependence. A retrofit costing ~5% of construction is a scalable, decentralised contribution to the country's Net Zero 2060 goal — and it builds energy literacy along the way.