Material area is not correct

[maarten.meerts]

I have used the door family (attached to this thread) in my project.
The folowing parts with material parameter are drawn in this family:
- The door (BE Deurblad Materiaal)
- the frame (BE Vast Kader Materiaal)
- the beam that supports the bricks above the door (BE Linteel Materiaal)
- the profile under the door that is used to seperate the floorfinishing. (BE Tussendorpel Materiaal)

I gave only the beam a material
When I extracted the area and the volume when it was placed in a wall, they were both not correct.
When I gave the profile a material (different from the beam) then the volume of the beam was correct but the area still wasn't.
I've searched what number the diplayed area is equal to. And I found it. The area that is displayed in the skedule is the sum of the areas of the 6 faces of the beam.
Does anyone can explane this? What can I change to the family to get the correct area?

Thanks