Superficial area method is the most popular preliminary estimating method. Floor area method of estimating facilities costs is frequently used in building and residential home construction. This method is an approximate cost obtained by using an estimated price for each unit of gross floor area. The main reason for the popularity of the area method is its simplicity.
Floor Area Estimate = Area of each of the floors x Cost per m2
There are few rules to remember and the cost per square metre is well understood by property developers.
- Measured at each level to internal face of external walls
- No deductions made for stairs, internal walls, other internal partitions, lift zones, columns and the like
- Special items should be excluded and added to overall cost calculated
Previous similar building costs are used by dividing the construction cost by the internal area. Adjustments can be made for location and inaction, but specification adjustments are much more difficult to estimate. Subjective judgements are made for size, shape, the number of storeys, services, ground conditions and standard of finishes. A separate assessment should be made for external works, demolitions, incoming services and drainage which can be signicantly different for similar buildings.
The unit method estimating is not practicable for some type of buildings such as warehouse projects or open-plan offices. In that case, the superficial floor area method is found to be reliable with an accuracy of 10% to 15%.
Floor Area Method also works well with certain external works contracts such as concrete paving or macadam surfacing.
Superficial Floor Area Method Estimating Example
Sometimes contractors are asked to quote for building work using sketch drawing sand a square metre price.It is unlikely that a contractor would risk signing a contract on this basis. First, a clear scope of works would be needed together with a site survey and soil investigation report. The price must accurately reflect the amount and specication of works.
Floor Area Method Estimating Advantages
- Quick method
- Easy to employ as the rules for calculations are much more simple
- Directly relates to accommodation
- Allow comparison of different Designs
- Meaningful in its concept of measurement(m2) to both client and architect
- Allow comparison between buildings that differ in size and shape
Superficial Floor Area Method Estimate Disadvantages
Fails to take account of any variation in plan and shape or storey height