Unlike allowances, which cover specific items, contingencies are funds set aside to cover unforeseen items during the construction process. These could include unexpected site conditions, design errors or omissions, or unforeseen changes in market conditions, like a sudden increase in material costs.
For example, a conceptual estimate may have a contingency of 20% and an allowance of 10%, while a detailed estimate may have a contingency of 5% and an allowance of 2%. However, these percentages are not fixed and may vary depending on the project characteristics and the level of confidence of the estimator.
Typically, most construction projects use a contingency rate of 5% to 10% from the total project budget. This is typically enough to cover any unexpected costs that may arise throughout the project.
While both relatively simple concepts, allowances and contingencies are often confused with one another. Conflating the two can lead to pitfalls. An easy way to remind oneself of the difference is: allowances are for known unknowns, and contingencies are for unknown unknowns.
The contingency allowance is the time allocated during planning for unscheduled events. Technical and personal disruptions result in changes in the indirect production costs. The contingency allowance is calculated in special contingency time studies, the results of which yield rates for indirect production costs.