I have prepared a model of a house, and would like to know the vertical roof area in order to calculate its ability to collect rainwater. When calculating a building’s ability to collect rain, we assume that all rain falls vertically. Therefore, the pitch of the roof doesn’t matter.
This is not the same as measuring the actual area of the roof, since the roof is sloped. I simply want to know the area as it appears in parallel projection, i.e. straight down. The building isn’t a simple rectangle so trying to calculate this by hand is quite a lengthy process of summing together all the separate pieces of the roof, which are at different heights.
Is there a quicker way to achieve this? One idea that springs to mind is that I could create a large rectangle (bigger than the whole house) and then use the house as a ‘cookie cutter’ to cut out a piece from the rectangle. The area removed from the rectangle would represent the area of the roof area. But how to do this? Or is there another way I haven’t thought of?