The superficial floor area also known as the square metre method of estimating is one of the quickest methods of calculating the cost of a building/construction project. It is the first estimate that will be prepared by a Quantity Surveyor when initial sketch drawings are produced by the architect. In this early planning and design stage, an architect may produce design alternatives that can be priced by a Quantity Surveyor for cost comparison purposes. Alternatively, the architect may design to a cost taking into account the client’s budget.

The square metre method involves measuring the internal gross floor area of a building and multiplying by the cost per m2, to get the total cost of building. The internal gross floor area is measured within the external walls (i.e. floor area enclosed by external walls) without adjustments for partition walls, staircases or lifts. For example when measuring a simple rectangular single storey plan (20m x 5m) with 230mm external brickwalls and no open space, in a location where the building rate is R8,000 per m2, you have to calculate the cost of building as follows:

First Step: Calculate the inside length of external walls (measured from inside face):

20m – (0.23 x 2) m = 19.54m

5m – (0.23 x2) m = 4.54m

**Total Estimated Cost of Building Project = Internal Gross Floor Area x Cost per m2**

**Total Cost = (19.54 x 4.54) m2 x 8000 **

**Total Cost = 88.71m2 x 8000 **

**Total Cost = R709,680**

__Building with Open Spaces__

For a building with open spaces (e.g. enclosed courtyards, areas under roof lights, veranda, porch, patio etc), you will need to adjust the internal gross floor area by deducting the area of the open space.

In this case, if the same single storey plan (20m x 5m) has a corner veranda measuring (3 x 1.5) m, you will need to adjust the gross floor area of the building:

__Building Area:__

19.54 x 4.54 = 88.71m2

__Veranda Area:__

3m – 0.23m = 2.77m

1.5m – 0.23m = 1.27m

Area = (2.77 x 1.27) m = 3.52m2

__Adjusted Gross Floor Area: __

88.71 – 3.52 =85.19m2

**Total Estimated Cost of Building Project = 85.19 x 8000**

**Total Cost = R681,520**

__Multi-storey Buildings__

When estimating or measuring buildings with multiple storeys or floors, the concept is the same. You have to adjust the internal gross floor area of each floor for open spaces such as balconies and decks.

Whereas you can use a single rate when pricing a single-storey building, an experienced Estimator will analyze the floor specifications in each room, so that an appropriate rate can be applied to that room. In a luxury or exclusive house designed by an architect, the types of floor finishes may vary across rooms – for example, such a house might have a tinted grano floor in the garage, terrazzo floor in the kitchen, ceramic tiles in the bathroom, marble floor in the living room and carpets in the bedroom. In this case, the Estimator has to measure the rooms separately so that the floor finishes can be appropriately priced.

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[…] « Square Metre Method of Estimating – Advantages and Disadvantages [Building Construction] […]

[…] Superficial Floor Area Method – Once sketch designs with floor areas are available, the Estimator can measure the internal gross floor area of the building and multiply the same by the construction cost per m2. According to data provided by local municipalities, building societies, property developers and consulting quantity surveyors, the construction cost per square metre differs by region, location and type of building. […]