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How to calculate the gross floor area of a building?

As you will have noticed, it is possible to define a minimum floor area for each individual space in BriefBuilder. This is usually done in terms of usable floor area (UFA): the amount of space that should be directly available for user activities, excluding ‘non-usable’ areas such as the space required for partitions or columns.

It is likely, however, that you also want to have an indication of the total size of the building in terms of gross floor area (GFA). That number does not only include the usable square meters, but also the square meters that are needed for technical installations, plant rooms, walls, columns and so on. This is quite a crucial number because it is often used for cost calculations.

To calculate the gross floor area of building or project, you can use the GFA/UFA ratio, which is a multiplier that is being used to go from usable floor area to gross floor area. This ratio can, for example, be 1.4 or 1.7, dependent on what type of building it concerns.

In BriefBuilder, the GFA/UFA ratio is available as a standard property of the object Building. You find that property on the detail view of a building object, but you can also find it in the area report that is available in the main menu under the header Overviews.

The area report is easiest to work with because that is where the total gross floor area is shown (in the last column in italics). The area report can be found in the main navigation menu, under overviews.

The GFA/UFA factor is a standard property of the object Building, as shown here. Please note, however, that you have to go to the area report to see the total gross floor area.
The Area report can be found under overviews
Click on image to expand. The last column shows the total gross floor area of the building in italics. Note that you can easily export this table to Excel (see the Excel icon next to the table name) for more detailed calculations.

There are many different ways of naming and defining areas in buildings. We recommend that you use the property’s description in the requirement settings to define what kind of square meters you are talking about.

You can also change the name of the floor size property in the requirement settings if necessary. The default name is usable floor area, but you can easily change that into something else (e.g. net internal area).

NB If you change the name, do not forget to change the name of the area ratio as well (e.g. to GFA/NIA). To do that, select ‘building’ in the standard properties menu).

In BriefBuilder, the GFA/UFA ratio is linked to the building as a whole, and not to individual spaces (as sometimes is being done). This is because the gross floor area includes technical areas, such as plant rooms, risers and elevator shafts, that cannot be linked to individual spaces.

Updated on 31 July 2020

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