topic Re: Correct way to calculate Exposed Surfaces with convex wall angles? in Project data & BIM

Correct way to calculate Exposed Surfaces with convex wall angles?

LucaLeo — Mon, 16 Feb 2026 01:20:45 GMT

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

Re: Correct way to calculate Exposed Surfaces with convex wall angles?

Laszlo Nagy — Sun, 15 Feb 2026 19:57:46 GMT

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.

Re: Correct way to calculate Exposed Surfaces with convex wall angles?

Mathias Jonathan — Mon, 16 Feb 2026 09:36:01 GMT

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

Re: Correct way to calculate Exposed Surfaces with convex wall angles?

Mathias Jonathan — Mon, 16 Feb 2026 13:24:51 GMT

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

Exposed Area parameter in Surface Schedules:

Re: Correct way to calculate Exposed Surfaces with convex wall angles?

Laszlo Nagy — Mon, 16 Feb 2026 14:33:15 GMT

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.

Re: Correct way to calculate Exposed Surfaces with convex wall angles?

Mathias Jonathan — Mon, 16 Feb 2026 15:29:05 GMT

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/Calculation-Schedule-Troubleshooting-Guide/ta-p/303554

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.

Re: Correct way to calculate Exposed Surfaces with convex wall angles?

marcoariveross — Mon, 16 Feb 2026 15:30:26 GMT

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

Re: Correct way to calculate Exposed Surfaces with convex wall angles?

Fra — Tue, 17 Feb 2026 01:06:54 GMT

Hello

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

Francesco

Re: Correct way to calculate Exposed Surfaces with convex wall angles?

LucaLeo — Tue, 17 Feb 2026 21:03:46 GMT

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

Re: Correct way to calculate Exposed Surfaces with convex wall angles?

LucaLeo — Tue, 17 Feb 2026 21:26:24 GMT

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.

Re: Correct way to calculate Exposed Surfaces with convex wall angles?

AllanP — Tue, 17 Feb 2026 22:03:28 GMT

The problem:

2 of these 3 walls should measure 1.6m

If i was trouble shooting this i would look at the 2 possible answers:

the reference lines are on the incorrect side

you can show the wall and beam reference lines under

View -> On-Screen View Options -> Wall & Beam Reference lines

a bug where the wall is accidently measuring the wrong side for some reason.

I would change ID's from MUR-089 to unique IDs so you can identify which one is failing.

there maybe another explanation that you have overlooked.

I don't know if this helps.

Re: Correct way to calculate Exposed Surfaces with convex wall angles?

LucaLeo — Wed, 18 Feb 2026 00:34:58 GMT

Hi everyone,

First of all, I would like to sincerely thank all of you for your replies and for the time you spent helping me — even just taking a screenshot and checking the result on your own computer with your version of Archicad.

Every suggestion and every screenshot I received was extremely helpful. They allowed me to run further tests, question my assumptions, and work toward solving the issue — or at least I hope I have solved it, since the latest tests have produced positive results.

The fact that some of you used the same version of Archicad as mine and obtained the correct result made me reflect. I therefore tried working in a completely new file, without the template I have been using for a long time, and started analyzing the differences in the schedule and in the way the geometry was constructed.

At one point, I even performed a simple copy–paste (Ctrl+C / Ctrl+V) of walls modeled in a new file without the template, pasting them into the file where I use my template. Even though the walls were identical, the results were still different: in the template file I was getting the incorrect value (20.40), while in the other file the result was correct.

By carefully comparing the different fields, I noticed that in the template file there was a missing layer component in the field. I first tried assigning all visible layers, then assigning a specific layer I had created, and finally even deleting that field entirely.

After performing one of these operations, the calculated surface areas became correct.

I ran additional tests by inserting windows — both with the frame set to the wall material and without — and by modifying the wall height (for example, changing them from 2 meters to 3 meters) to verify the results. The final outcome was positive: calculating perimeter multiplied by height gave the correct surface area.

I am attaching a screenshot showing the two windows side by side, to highlight the difference that was causing the incorrect result.

I still do not fully understand why this was the source of the error, nor whether this is the proper approach or simply something obvious that I had overlooked. I had never noticed this discrepancy while comparing the settings before.

At the moment, by a process of elimination, removing or reassigning that field resolves the issue. However, I still cannot understand why, despite never modifying that schedule, that parameter was missing in the template file.

If anyone has further insights or observations on this matter, they would be greatly appreciated. I would really like to better understand what happened.

Thank you again to everyone.