Calculating site coverage area while accounting for overlaps

[Paul Roper]

Hi everyone,

Is there a way to calculate the total area that multiple Elements cover (e.g. Roof objects), while accounting for any overlapping sections?

Referring to the attached example image: An Upper Floor Roof and a Lower Floor Roof, with part of the Upper Roof overlapping the Lower Roof. Adding up the areas of the two Roof objects gives an expected answer. The result I'm interested in is the area bounded by the black dotted line — the total area of the site that is covered by any Roof.

Is there a way to combine the area totals while automatically subtracting the overlapping area?

Alternatively, I would appreciate any workflow suggestions. I'm hoping to avoid creating an additional object, but I can't think of how to achieve that at the moment.

[Paul Roper]

Thank you Steve, I quite like this method...it will work for me.

[MitchD]

i like this method, it would work well for my contract drawings.... is it possible to express the 'rainfall' slab as a percentage of the 'site' slab for site coverage? that would take a few manual calcs out of my process.

[Barry Kelly]

To get the percentage of the rainfall area compared to the site area, unfortunately you have to start inputting manual figures.

The slabs can not share information with each other and the schedules can not do calculations (other than simple summation).

So you need to start using 'Properties' with expressions.

You will need to create a property to calculate the percentage of rainfall area to the site area.

This property must be associated to a classification that is used for the rainfall slab.

But you will also need a property for the site area also associated to the same classification.

The unfortunate part is you need to manually add the value for the site area, because as I said the slabs can not share information.

Once you have it set up, it is automatic.

And generally the site are does not change - set it once and forget it basically.

There is a lot to learn about expression based properties if you do not know about them already.

https://community.graphisoft.com/t5/Project-data-BIM/Expression-based-properties-FAQ/ta-p/303797

Barry.

[Barry Kelly]

Actually it could be done within the one rainfall slab automatically.

Because the size of that slab matches the size of the site, no need to manually input the site area.

Now you have the overall area and the conditional area, you just have to create a property with the expression to work out the percentage.

Barry.

[mthd]

Hi all above, it is important that flat rainfall area and site coverage area shouldn’t be confused.

We should know that when calculating rainfall areas on a roof plane that is inclined, that the area is increased by the angle of the slope. And each roof plane needs to be calculated separately to determine the gutter sizes and the number of down pipes needed in a particular rainfall area.

This is usually what an engineer would do and realistically, even the paving is sloped as well including so called flat roofs.

But definitely ok for calculating site coverage via SEO’s.