The persistent assumption in affordable housing delivery is that cost is controlled at the level of specification. In the models examined here, specification accounts for a minority of delivered cost. Land, servicing, plot geometry and finance dominate.
Four cost structures
Land cost per unit falls approximately linearly with density until the point at which structural system and fire regulation change. Identifying that inflection for a given regulatory environment is the single highest-leverage decision in an affordable housing project.
Servicing cost per unit behaves similarly, but with a second inflection where bulk capacity is exceeded and a new connection is required. Plans that ignore this produce a phase that cannot be occupied.
Plot geometry
Narrow, deep plots reduce infrastructure frontage cost per unit and support incremental vertical growth. They also require more careful daylight and ventilation design. The trade is almost always worth making.
What this implies
Affordability is a planning outcome before it is a construction outcome. By the time a specification is being value-engineered, the decisions that determined affordability were made two years earlier.