Figure 1 demonstrates decreasing the productivity rate or hours per unit by 30% because of a loss in productivity. If work must be performed at a height greater than the 8-10’ wall height assumed, it will take more hours per unit. If there is an increase in the price of material, that can be adjusted in this function. If scaffolding is necessary, an additional line item for it should be added.

Where there is increased difficulty in performing the work, think through the conditions for each trade. If the walls and ceilings must be replaced, then the demolition, replacement, masking, finishing and lighting fixtures would need productivity rates evaluated. An accurate estimate considers all factors necessary to complete the job. Notations on the estimate indicate the things accounted for, and the estimate may not be challenged. If price is challenged, the assumptions should be apparent for proper resolution of any estimate discrepancies. Variations in labor rates come from union or non-union labor rates or a lack of skilled workers. Most programs allow you to select closed shop (union) or open shop (non-union), thus factoring in this labor rate variation. It is necessary to understand the labor conditions in the area and job you are estimating.

Comparing Estimates From Different Platforms
Not every item necessary to estimate a building may be available in a computer estimating program. Be familiar with some of the printed construction cost guides including RS Means, National Construction Estimator, etcetera. These resources include many items and have volumes specific to electrical, mechanical, excavation, and interior finishes among others. There are square foot estimates for items such as electrical or mechanical systems within these guides. Square foot costs in some computer estimating programs may not be as accurate because of a lack of specificity. The printed guides tend to give more accurate square foot pricing through variables in quality and building type.

If the estimate presented is divergent from your own, a line-by-line or trade breakdown may identify the areas of disagreement. If you have not received a trade breakdown in an estimate prepared on one of the computer estimating platforms, request one. If the estimate is from a general contractor, a breakdown by trade should be available. Computer estimates based on the same scope and assumptions of difficulty should not have a significant difference. A difference of plus or minus 10% is not unusual.