Correct way to calculate Exposed Surfaces with convex wall angles?

[LucaLeo]

Hello everyone,

I am trying to obtain a correct automatic calculation of Exposed Surfaces through a Schedule in Archicad, using the “Exposed Surface” field.

In the case of simple geometries, the calculation works correctly.
For example, I created a small room with four walls, each 2 m long and 2 m high (so the plan only contains concave corners).

I assigned a specific finish (white glossy) to the external surface and activated the “Connected Walls” option.

In this configuration, the total exposed surface is calculated correctly:

4 sides × 2 m × 2 m = 16 m²

I have attached images for this first case.

The issue appears when the geometry includes convex angles (generated when the perimeter steps inward).

In these situations, the exposed surface value becomes higher than expected.

From what I can understand, at the points where two walls form a convex angle, the calculation seems to include an additional strip equal to the wall composite thickness where the surface is applied.

It looks as if a portion related to the wall thickness in plan is also being counted, which results in an overestimation of the actual exposed surface.

I have attached images showing this second case as well.

My questions are:

Is there a correct method to calculate exposed surfaces in this situation?

Or am I doing something wrong in my setup?

Any clarification would be greatly appreciated.
Thank you in advance!

Operating system used: Windows 10

[Laszlo Nagy]

Yes, interesting, it seems to incorrectly calculate areas in the second scenario. This may be a bug.

I don't know which Archicad version you used, but I tried Ac29 and it still does not report the correct values for some of the Walls.

Please report this to your local reseller.

[Mathias Jonathan]

is it a surface schedule (different than expsoed surface from an element schedule)?

[Mathias Jonathan]

Surface Area of the Wall Out­side Face in an element schedule:

Exposed Area parameter in Surface Schedules:

[Laszlo Nagy]

As for me, I tried the usual Surface Area parameters on the Outside/Inside, and those, too, gave incorrect results for some of the elements in the convex angles case detailed above.

[Mathias Jonathan]

 

The subject emerged in archicad 17 with building materials (Link not online anymore): https://web.archive.org/web/20231202223150/https://community.graphisoft.com/t5/Project-data-BIM/Calc... 

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Issue and Cause

With Priority Based Connections in ARCHICAD 17, the calculation of wall areas has changed.

• Up to AC16, an L shaped connection created a 45 degree mitered joint at the corner. This resulted in the two outside surface areas to be equal.

• In AC17, in an L shaped connection one wall will be prioritized over the other (more similar to a real life building environment) and the edge of the wall is not counted into the areas. Thus the wall areas are unequal and seem erroneous.

Solution

• Through the development of a design, a thin layer of paint can be applied to the composite material, thus the area calculations will be accurate. As in the image above, the thin edge area is small and insignificant in the calculations.

There are 2 important points to consider:

•  
• The decimals have to be set to 1 in the "Project Preferences"
• The minimum layer thickness for the calculations to work is 0.1mm.

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[marcoariveross]

Hi, I just tried it in AC29 and it gives me the correct results.

[Fra]

Hello

I don't know if I'm doing something wrong.
The calculation seems correct to me, in ArchiCAD 28

Francesco

 

[LucaLeo]

Thanks a lot for your reply, I am using Archicad 28.

[LucaLeo]

Thank you very much for all your replies, for the links you shared, and for the explanation you provided, describing the issue and how it was solved in Archicad during the transition from Archicad 16 to 17. It could be a good compromise or a useful method to overcome this issue. After trying it, the dimensions actually appear to be correct. So thank you, and I will keep this as a possible solution to the problem.