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Abstract:The adoption of incremental owner-built techniques in housing construction relies on the associated lower cost compared to developer-built approaches. The mechanism that lowers cost is however, not obvious. This study is based on survey data that were collected using questionnaires which were distributed to 200 respondents in Dar es Salaam, Tanzania with response rate of 22.5%. The analysis results, based on descriptive statistics and regression analysis indicate that an incremental house-builder targeting an additional bedroom incrementally spends 28% lower annual construction cost and each additional square meter built, is associated with 0.4% lower cost. However, such lower cost comes at a 5%-10% longer completion time. These observations suggest that spreading costs over time reduces construction cost through multiple cost-saving channels opened up by time itself and factor intensity. The intensity of incremental housing construction favours increasing expenditure on labour than capital yielding a 5% reduction in annual cost but the greatest cost reduction benefit of up to 26% is realised through increasing expenditure on "capital" with fixed spending on materials during construction.

The owner-built incremental housing strategy has been used for many years across the developing world. This study examines the implication of construction constraints and challenges on annual construction cost expenditure across housing types. Using descriptive statistics and correlation analysis for 43 incrementally built housing units implemented in Dar es Salaam between year 1993 and 2013, the study has observed that single and two-storey incremental housing builders face the same set of human related construction challenges and external cost-push factors but different administrative, physical and interest related constraints. Of all the cost-push factors examined, interest rate intervention is the only observed strategy that has far reaching potentials to single-storey low cost incremental builders because such builders are less likely to resort to loans as a mechanism to finance housing. These findings suggest that any other external efforts targeting physical or human related incremental construction constraints are likely to end up either benefiting the high quality builders or every incremental builder regardless of cost or property type or both. The study argues in favour of targeted interest rate support rather than physical or administrative housing assistance if owner-builders are to benefit specifically in any housing policy support.

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