Saturday, November 09, 2013

Foundations and Insulation Calculation

I got involved in a thread at that asked about calculating the total bitumen insulation required to cover concrete foundation surfaces. The original post described using the Paint tool and how much time it took. I always wonder if people are responsible for the calculations or just curious whenever I read such requests. Sometimes I ask. Intellectual exercises might be interesting but they can waste a lot of time if the results don't actually get used by someone.

Since I put the effort into it already I decided to use this post to share the example project I created in response. I shared an earlier version in the thread but this one has more ideas expressed.

I'm inclined to try to use schedules and formulas to calculate/predict the insulation material required instead of using paint and a material takeoff. The Isolated Foundations (footings) have one form (most of them) so there aren't compound layers like foundation slabs, floors or walls.

It isn't as simple as just reporting all the surface area of each kind of foundation. It isn't even simple to do just that. The surface touching the ground doesn't get the insulation (my understanding in this situation). No insulation is required where a column sits on a footing so we need to subtract the column base area from the top of footing surface area. No insulation is required where a wall sits on a footing either.

We also have parameter inequity. Isolated Footings don't have a "thickness" parameter. Foundation Slabs and floors do. Inconsistent application of dimensional values is the sort of trouble we face when we use the provided family categories (as their naming/behavior implies we should) and try to compile their information using the "same" notion of dimensional criteria. They just aren't all equal, they don't have the same "beliefs".

My approach started out with a foundation schedule that includes footings and slabs, a schedule for walls and a third for columns. I needed to distinguish between footings and slabs so that I could create formulas to figure out the area for the top and sides of each kind of footing. Floors and Slabs have Default Thickness and Perimeter. When they are rectangular they also have Width and Length. If they are irregular they don't. Foundation footings don't have thickness but have Width and Length.

I used a formula to divide the Volume to arrive at an Approximate Height to use to calculate surface area for top and sides. I used a parameter called Is Slab (an integer) so my Bitumen formula could decide which formula technique applied. I just enter a 1 for slabs and 0 for footings. This is the foundation schedule for wall footings, isolated footings and slabs/floors.

As you can see I added some rows to the header to explain the empty cells in the schedule. I also added the formulas (after capturing the images) to the comments so it's possible to validate the results without having the model.

Here's the schedule for the walls. I've not resolved the overlap of walls onto footings or the walls and their own footings in the schedule above. I'd probably create another schedule for subtracting the bottom surface area of the walls, or if possible include it in this one.

And here's the schedule for the columns, I put the (-) in the header to make it a little more obvious that the area should be subtracted from the other totals.

You may already know that columns don't have a base width or length parameter that we can see in schedules. They have a type name but the parameters that govern their base dimensions are called "b" and "h", like the corresponding graphic in some structural design manuals I've seen. I added two shared parameters, Base Width and Base Length, to the column family and just made them equal to "b" and "h". That's probably the easiest way to resolve content that fails to use system parameters that are compatible with other families, as well as content that you download and find the same conflict between other content of the same category.

Assuming the approach above is completely uninteresting these are some possible alternatives we could consider.
  • We can "paint" on materials and there is a Split Face tool which will work on floors, foundation slabs and walls but not structural foundations or columns. We can model all foundation elements as floors and/or foundation slabs which would make it easier to use the Split Face tool and then paint on the insulation.
  • Use a combination of the schedules above and some use of the Paint tool and material takeoffs.
  • We can create separate families for the insulation conditions that can be scheduled by themselves, or at least for the foundations that can't be "painted" with Revit's paint tool.
  • We can build more complex footing families that have an additional form(s) for insulated surfaces and these can in turn be used to define them in a material takeoff, instead of a regular schedule.
  • A talented programmer with the Revit API could take into account all sorts of permutations and generate a pretty comprehensive summary).
I've posted the project file if you'd like to DOWNLOAD IT. Happy insulating!

1 comment:

Steve said...

Julien Benoit at offered an interesting option that reminds me of measuring the weight of 10 bolts to count hundreds of bolts.

He described creating a mass element that surrounds all of the footing elements, taking note of the mass area and then joining geometry of the mass with all the footing/foundation elements.

When you subtract the area of original mass you'll have the surface area of the foundation elements.

That will include the bottom of the foundation elements. If they are not supposed get covered with the same insulation then we just need to subtract that surface area to get pretty accurate result.