topic Re: Calculating site coverage area while accounting for overlaps in Modeling

Calculating site coverage area while accounting for overlaps

Paul Roper — Wed, 24 Jan 2024 21:47:35 GMT

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.

Re: Calculating site coverage area while accounting for overlaps

Marc H — Thu, 25 Jan 2024 00:36:44 GMT

Hi Paul,

Are you looking for the net flat (in plan) area, for say, rainfall calculation, or the net sloped area of the roofing, for say, costing purposes?

Re: Calculating site coverage area while accounting for overlaps

Paul Roper — Thu, 25 Jan 2024 00:47:00 GMT

Hi Marc,

Good question. I'm looking for the net flat area (in plan) for things like rainfall calculation.

Re: Calculating site coverage area while accounting for overlaps

Marc H — Thu, 25 Jan 2024 00:48:25 GMT

Could you just use the gross area of the lowest roof or do you need a break-out?

Re: Calculating site coverage area while accounting for overlaps

Paul Roper — Thu, 25 Jan 2024 01:08:53 GMT

In this case, that could work! I wasn't able to find a Field in my Schedule Scheme Settings that reflects this value. Perhaps you could help me in that regard?

For other cases however, this method may not work:

If possible I would also like to be able to account for overlaps with other impermeable surfaces (tiled patios / paved concrete driveways) that I often model from slabs or meshes:

Let me know your thoughts.

Re: Calculating site coverage area while accounting for overlaps

Barry Kelly — Thu, 25 Jan 2024 01:14:53 GMT

If it was me, I would simply add a fill to represent the site coverage.

I know it is extra work and not linked to the elements so will not change automatically, but it is probably the easiest solution.

Barry.

Re: Calculating site coverage area while accounting for overlaps

Paul Roper — Thu, 25 Jan 2024 02:13:03 GMT

Thanks Barry, yes that's pretty much what I currently do. It's usually fine...

Occasionally I find myself working on a renovation project where I am creating a Fill for the Existing, To Be Demolished, and New impermeable areas for clarity of presentations to local body authorities.

It's not always much extra work — but it can be — if, say:

the local body wants to see the various categories of impermeable areas tallied separately (multiplying the number of Fills I need to create)
One side of the roof is being demolished
Another side of the roof is being extended
a third of the driveway is being remodeled
this corner of the patio is being extended
a week later a change in budget dictates a design revision
etc.

In some such cases I've found myself changing dozens of Fill outlines in order to update all the relevant totals that the local body authority likes to see.

The painful part is my awareness that software could be programmed to do it automatically. Maybe it's just one of those things ¯\_(ツ)_/¯

Re: Calculating site coverage area while accounting for overlaps

Steve Jepson — Thu, 25 Jan 2024 02:37:33 GMT

You could SEO holes in a slab using items in a Layer Combo and schedule the top surface area of the Target. Something like that ?

Re: Calculating site coverage area while accounting for overlaps

Barry Kelly — Thu, 25 Jan 2024 03:43:21 GMT

That is actually a very good idea - the areas can all be automated with SEO.

Place a slab the size of your site (site slab) - can be in layer you can hide.

Now you can do Solid Element Operations (subtract with downward extrusion) for all roofs, gutters, paving, etc.

Whatever you are considering for your rainfall collection area.

You can get the areas of this slab, but I can see no way to get the actual 'hole' area without manual calculations.

However add another slab (again in a hidden layer) that is your 'rainfall area slab'.

SEO with downward extrusion the 'site slab' from the 'rainfall slab' and the area of that slab is your rainfall collection area.

So, as long as you keep all of your SEO connections up to date, you know have an automatically updated rainfall connection area.

It is not the ideal solution, but I think it should work.

Similar can be done for site coverage.

Barry.

Re: Calculating site coverage area while accounting for overlaps

Steve Jepson — Fri, 26 Jan 2024 01:55:55 GMT

I do it like this.

Place a big SEO slab/zone... whatever, the shape of the lot. Subtract with upward extrusion. Schedule the surface area for the top.

However, it is not that much trouble to stretch the nodes of a fill either - which will also update an Interactive Schedule. This is typically a task that takes place after all the modeling is done anyway. So it's not going to be changing much or very often.

An advantage of using the Fills is that the Interactive Schedule data cab be verified with the Show Area Text on the Fills. And also, I like to have the fills used for this with the ability for cover fills for asphalt, grass, gravel, concrete .... If it's in a Schedule, I like to make sure it is verifiable - not just blind data. My Layouts with Interactive Schedules usually have graphics or some kind of drawing next to them.

Re: Calculating site coverage area while accounting for overlaps

Paul Roper — Mon, 29 Jan 2024 21:48:34 GMT

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

Re: Calculating site coverage area while accounting for overlaps

MitchD — Fri, 09 Feb 2024 01:28:41 GMT

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.

Re: Calculating site coverage area while accounting for overlaps

Barry Kelly — Fri, 09 Feb 2024 02:45:42 GMT

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.

Re: Calculating site coverage area while accounting for overlaps

Barry Kelly — Fri, 09 Feb 2024 02:50:14 GMT

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.

Re: Calculating site coverage area while accounting for overlaps

mthd — Wed, 21 Feb 2024 03:48:00 GMT

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.