Volumes & areas of walls

[Yancka]

I'm trying to use worksheets and their functionality for calculating volumes and areas of wall materials, but find some things stumbling.

My wall is 15 mm stucco, 300 mm light concrete blocks, 100 mm heat insulation. 15 mm stucco. Total 430 mm.

1. Is there a way to calculate volumes of components of wall?

I need volumes for light concrete blocks and heat insulation. If I enter =VOLUME(...), I get volume of all wall. I thought about adding some coefficient after like =VOLUME(...)/430*300, =VOLUME(...)/430*100, but it isn't perfectly correct because inner perimeter is different from outer perimeter of walls and proportions of wall components are different (300/100).

2. How do I get in worksheet inner and outer areas of walls?

I tried to use WALLAREA_NET function, but it doesn't show exact value. I draw square of walls 4x5m, delta Z = 3m, in worksheet cell type =WALLAREA_NET(...) and get the value 59.16. But 4x5x3=60. Where VW loses 0.84 sq.m.?

Later I made another walls which at some point look like zig-zag and in this case WALLAREA_NET function gave me number (89.16) witch as I later discovered, is mathematical middle number of inner perimeter (84) and outer perimeter (94.32).

How do I get wall area of inner side and outer side? I'll need these numbers for correct amount of color. The difference of what VW shows and what actually in this case is +/- 5.8%. That's a lot if amounts are high!

Thanks in advance!

If any other good experience for these or related tasks - go ahead, I'll be glad to hear anything concerning automating calculations, wall creation tricks, ...anything.