1.   The possibility of overspending due to inevitable inaccuracy in the estimate should be guarded against by the inclusion of contingency sums.

2.   The amount of the contingency sum should reflect the degree of uncertainty in the definition of the project and the firmness or otherwise the budget.

3.   If the intention is to justify to the source of funds the need for additional finance as circumstances arise, the contingency sum can be lower.

4.   A further contingency sum or reserve should be kept for the project manager to deal with matters outside the control of the design teams.

5.   As the size of the contingency sum reflects on the degree of uncertainty, the amount of the sum required should decrease as the project proceeds.