NBN EN 15221-6 & NEN 2699 a practical guideline to measuring & benchmarking the outside of a building

Analyzing an office building I encountered some issues concerning measuring the outside spaces according to the NBN EN 15221-6. The standard is quite clear but one has to consult several pages. Hence a practical guideline.

For people not familiar to this standard, the hierarchy of floor areas [1] in the building according to table 1 looks like this:

This breakdown is mandatory for all categories of areas.

The standard distinguishes between:

  1. spaces which are entirely covered and enclosed on all sides up to their full height
  2. spaces which are entirely covered, but not enclosed on all sides up to their full height (e.g. recessed balconies)
  3. spaces which are not covered, but contained within components (e.g. open balconies)


The definition of Exterior Construction Area (ECA) is a measured area consisting of the exterior walls of a building envelope finished surface. The additional figure 8 in the standard is pretty straight forward.

In order to enable benchmarking one needs to establish a relationship between the NBN EN 15221-6 concerning measurement and the NEN 2699 concerning investment and operating costs of real estate.

For some Elementclusters this is rather clear.

  • B1A Foundation can be related to the Building Footprint
  • B1B Bearing construction can be related to the Gross Floor Area


But how to benchmark the cost of the façade in the following situation?

I have drawn the figures of the NBN EN 15221-6 on the sketch. One sees that the Exterior Construction Area (ECA) contains a Net Floor Area (NFA) in its breakdown.

Now, elementclusters on level 3 of the NEN 2699 are used for benchmarking in order to be able to quickly estimate mass studies used in Stage 1 Preparation & Brief of RIBA plan of work. Therefore, one doesn’t measure all the curves within the ECA area (thick blue dashed line) but the straight vertical surface of het outside of the ECA area (thick blue full line).

However, keep in mind that, when benchmarking all the costs of the window, floor & ceiling finishing of the terrace, the parapet and façade finishing itself need to be related to that straight vertical surface. Only then one gets the right cost index for the façade when one has a design like the one above in mind.

The initial breakdown can hence be extended to:

[1] Floor areas are measured at floor level at the height level to the top of a finished floor.