I know revit has some little inaccuracy with material takeoffs when joining elements but this is a big one.
SCENARIO: A floor that is JOINED with a wall but the floor doesn`t cover all the thickness of the wall just some layers. Metric units used. Unit = meters(m)
1) The PENETRATED element:
A wall with 4 equal layers(4 x 0.1m thickness); Wall Length = 1m. Wall Height = 2m
Wall Area = Every Layer Area = Length x Height = 1m x 2m = 2 square meters.
Wall Volume = Thickness x Length x Height = (4 x 0.1m) x 1m x 2m = 0.8 cubic meters
2) The PENETRATOR element:
A floor with one layer(1m thickness). The Floor penetrates in 4 stages(for every wall layer component) the wall. The floor has the same length as wall has (1m). So the problem is very simple to calculate the Area and Volume directly in mind when watch the pictures below even if you are used with imperial units. It`s pure arithmetic:
a __nonpenetrated_wall_layer has Area = 2 sqm ; Volume=0.2 cubic meters
a _____penetrated_wall_layer has Area = 1 sqm ; Volume=0.1 cubic meters
(penetrated layers have half values for area and volume)
You`ll see that the resulted numbers that revit calculates are so wrong when you penetrate just some layers from the wall that I`M WONDERING: HOW CAN YOU RELY ON REVIT IN THIS CASES. You can loose clients with so big mistakes.
Ok i know that because the floor has a big thickness(1m) related to the height of the wall(2m) the mistakes that revit does are amplified a lot. But even if the floor is thinner in reality you have very long walls and floors so the mistake will be amplified by length parameter. So no escape.
WHAT DO YOU RECOMMEND?
I observed that the area and volume for entire the wall schedule (that`s below the material takeoff) is ok so the solution could be a calculated value with percentage per layer thickness relative to wall thickness and then substract the a calculated volume from floor intersection?
Or not using the JOIN tool if the thickness of the wall is not fully covered by floor? So you have to abuse the layer extensions and edit wall sketch or draw walls by layer to replace joining effect. This will make thinks too complicated. Because Join tool meke your sections look beautiful very fast. I rather make material list by hand then killing the Join tool.
Attached 5 images for every stage. Pictures are the best because there are marked corrected value and the percentage between revit errors and the real value.
And the movie (you ca use PAUSE to analyse)
AGAIN: WHAT DO YOU RECOMMEND?