In construction projects, plans and cost estimates are usually drawn to ensure that the work is carried out to the desired quality, within time and budget. The construction industry is inherently uncertain due to nature of the industry itself which often times makes accurate cost of project near impossible thereby given rise to the inclusion of contingencies in order to meet project objectives. Therefore, the study assessed the relationship between contingency sum and client objectives (cost, time and quality) in order to ensure effective project delivery in the renovation of public school facilities in Abuja. This was done through the self-administration of 331 structured questionnaires and historical data from 100 renovated projects between 2001 and 2011. It was discovered that location of the project, the level of dilapidation, type of project, volume of work and duration of the project determine the percentage addition of preliminary sum to the total cost of renovation work. Based on this, actual contingency sum should always be considered bearing in mind these factors in renovated work