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Slab layers - newbie question


mr. iagea

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hi.

i'm new to VW and i have what may seem a rudimentary question: i need a good definition of "slab" as it pertains to the floors in multi-floor buildings.

is "slab" simply the complete floor thickness, including finished flooring material? is the measurement taken from the bottom of the joist (assuming a wood frame) up to the top of the finish floor in the next floor up, or is the measurement taken from the "bottom" of the ceiling material up through the next finished floor material?

perhaps a corollary question would be what are the boundaries of a mod-level (ceiling to ceiling or floor to floor?), and at what exact point are those boundaries limits?

and then, what is the "slab layer" in the model setup command.

thanks in advance!

charlie

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I think perhaps the answer to these questions is that these things are what you as the creator want them to be. You be THE DECIDER, for better or for worse. 'Slab' usually refers to the floor structure, but it may be convenient sometimes to push some other stuff into that thickness.

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I use slab layers for the floor structure. I also put stairs on the slab layers so that I can move them behind floor openings. I run my exterior walls from top of floor to top of floor and create the floor slab inside those walls.

Some folks don't use slab layers at all. They use the Structure-Slab class and keep the slab on the Mod-Floor layer. I frequently generate interior perspective renderings so I keep the slab on it's own layer. This allows me to turn on the slab above (seen as ceiling in rendering) independent of the walls and other items on the floor above, thus reducing render time.

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thanks, brooke and billtheia.

what i'm trying to find out is what VW considers a "slab layer" in the "Model Setup" command (File > Document Settings > Model Setup). This is important to creating the proper elevations for the model building.

And, while i'm certainly flexible enough as a designer to make my floor slab consist of all sorts of parts, i would like to know where that is actually defined. is there a standard that determines what parts to include in a floor slab, i.e.: is it framing only, or finish materials also? does it include the ceiling material of the floor below or exclusive of that?

all this can affect the true elevations, and if i'm to assume that VW is helping me draw a virtual building, then those details are important (they are to me and my perfectionist streak, anyway).

eh?

cheers,

charlie

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what i'm trying to find out is what VW considers a "slab layer" in the "Model Setup" command (File > Document Settings > Model Setup).

I'm interested in hearing NNA's answer to this as well.

The fact that we CAN include many things in our slab layer doesn't mean we should.

Every tool, procedure, and dialog in VW was designed to be used in a specific way. Unfortunately, the help manuals give very little info on the reasoning behind these methods.

The fact that there is great flexibility is wonderful, but it is impossible to 'think outside the box' when you don't know WHY things are in the box in the first place.

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If I want to be really perfectionist-

my slab layer will have 3 'floors' - ceiling, structural and flooring - each on a different class. That way I can actually dimension to structure when I need it , or to finishes, turning classes on and off. (and texture those classes differently)

It makes the model set up a little more tricky - is the floor height 8' or 8'1" or 9'1"? But you can get a system going.

tali

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Charlie, Et Al,

At this point, I am going to beat the "BIM in Practice" web page drum again. There are a couple sample projects which address "best practices" for many issues, including this thread.

In the Ellicott Heights project, ALL elements of the structural system (cast-in-place concrete) are included in the 'Mod-Slab-?' layers. This takes into account the monolithic nature of the construction, the workflow that assumes that the structural design will be done by an outside consultant and the project file setup that uses DLVPs extensively. Note that the Stairs are included.

In the Alexandria Lofts project, the floors, stairs and a few miscellaneous items, such as pads, stoops and sloped roof surfaces, are included in the 'Mod-Slab'?' layers. In this case there are separate layers for the framing of the floors. The project file also assumes that all "work" done to the model (e.g. architectural, structural, MEP) and drawings, is handled 'in-house'.

So, which information goes on which layer does depend on a number of factors, which include the following:

- File structure (single vs. multiple references)

- Project size

- Workflow/division of responsibilities

- Level of detail to describe systems

This list is hardly exhaustive, but you should get the point.

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"Slab" and "Mod" are not special terms other than to be placeholder names that are assigned to automatically created layers. Rather than risk breaking my pick on the logic of Slab and Mod and where one thing stops and another begins, I'm much more effective if I make my layers one by one as my projects are almost never similar.

The Model Setup tool may be worth your time if you do the same kind of projects again and again, or if you are handing off data for someone else to input. I could be wrong.

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thanks, everyone!

this is good info?all good points, although i can see that there is a real nebulosity with the definition of "slab layer"! i don't feel so daft now.

i agree with boxjoint's comment. i have found the manuals helpful in indentifying the tools and commands of the software, but not a lot of information about WHY i would use one tool over another (and yes, i understand the concept of maintaining dynamic workflows in software). i have searched high and low for a definition of "slab layer" and i cannot find it anywhere (websites, books, even the training manual and CD's).

ah well...i will investigate the BIM in Practice example files and see if clarity surfaces. thanks for that info, Jeffrey.

thanks, all. i will post to this thread when i find a definitive answer.

charlie

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i have searched high and low for a definition of "slab layer" and i cannot find it anywhere (websites, books, even the training manual and CD's).

I've had this happen on quite a few occasions. Very frustrating.

If a term (such as "Slab Layer") appears in the program, especially if it is in a dialog box and part of an action sequence that requires input from the user, it should be clearly defined in the VW manual.

And the definition should NOT be as follows: "Slab Layer= A layer which contains the slab". There are too many of those already.

I once started keeping a list of "undefined" terms that I ran across. If I can find it, I'll post it.

Edited by boxjoint
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  • 4 months later...

re-opening the issue.

i STILL do not have an answer to this important question.

anyone know? what, exactly, is the VW definition of "slab" and "slab layer".

to what is the dimension? floor to floor? ceiling to ceiling? ceiling to floor above?

thanks!

charlie

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Charlie,

From the programming/computer engineering side, a "Slab" is a general term for a VW primitive geometry/behavior. Floor, roof faces, and pillars are slab-based objects. They are geometries defined by a 2D/plan profile and an extrusion height and they can "contain" holes of arbitrary plan geometry.

The "Slab Layer" was a nomenclature that first appeared with the advent of architectural functionality in VW. The idea is that a building story can be composed of multiple layers. Each layer would contain the geometry/objects for a particular purpose or realm of construction. Thus there are Mod-Slab-?, Mod-Floor-?, Mod-Lighting-?, Mod-Electrical-?, Mod-Plumbing-?, etc...

The Slab-layer-? was meant to "contain" the floor/ceiling structure (floor object) between building stories.

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Perhaps this question would warrant a new thread, but I think it's related enough: how do people handle floor & ceiling finishes in their models?

So far my 3D modeling has been very limited, but as all of the height information pertaining to light wood framing here in the U.S. relates to top-of-slab, top-of-subfloor, or top-of-plate, this is what I've been assigning the Z values for the floor and slab layers to. I've been drawing slab objects that reflect the overall size of the structural components (floor joists + subflooring), so the finish materials would be extra. If I want the finished floor or ceiling to show up in a section, I guess I'd need to add separate objects. Any thoughts?

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Jeff:

Good info. Thanks. Okay, so slab layer is a layer to contain floor objects. Good enough. So, how is a floor object defined (goes back to my original question)? I'm interested in dimensional characteristics (I sort of already assumed that slab layer referred to floor objects).

Say I run the Model Setup Command. I want a building with two floors and a simple foundation and roof. I get 6 layers after running the command. Foundation, Roof, Floor 1, Floor 2, Slab 1 and Slab 2.

What then am I drawing on the slab layers? Floor framing? OK, I can see that. No problem. Back to my original still-unanswered question: where is the slab layer measured from and to? Is it bottom of joist to TOFF (in the first floor)? In the case of the second floor, is it then bottom of drywall on the ceiling of Floor 1 to TOFF on Floor 2? Clearly there are differences, since most of us don't drywall the crawlspace "ceiling". Are those differences edited using the Z and Delta?

It might seem pedantic, but I want to know what VW includes dimensionally in the slab layer. This seems like a very rudimentary concept and I have not found the answer in ANY of the VW literature I have (which includes all the training CD's).

I think the answer to this will directly address Markus' question, or at least help get closer to a clear solution. I'm interested in that info, as well.

Also, something to consider: Using the Alexandria Lofts file as a model, the stairs are placed on the Slab Layers. This is confusing. How can a full flight of stairs be place on a layer that is supposed to contain only floor objects? Clearly there isn't enough room, and this was verified by my attempt to placed a 9' case of stairs on a slab layer and I got the text response: "Not enough space between floors to place stairs".

Thanks!

charlie

Edited by mr. iagea
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Charlie,

First, the "name" of a layer is COMPLETELY arbitrary; it is a label for the users' purposes only. So whether or not it is named "Slab", "Floor", or "RCP", that is up to a workflow/organization by the user.

Secondly. Layers are spatial containers within the "absolute space" of the VW file. Anything drawn/modeled in VW has to reside within a layer. Layers are related to each other by their Z-axis value. This value is user defined and can be manipulated at anytime in relation to other layers. Layers can share the same Z-value or have "stacking" values or have completely arbitrary Z-axis relationships. Think of layers as pin-drafting mylar sheets that can be stacked, shuffled, and restacked according to the needs of the drafter. The layer's Z-value is always in relation to "absolute Z=0" of the file.

At the same time, layers have no real height (delta-Z value). But the user can define a "height" to each layer. It is also an arbitrary, user-defined value that the program uses for objects/commands like walls, and the user implements for reference purposes. Right now, layers aren't explicitly linked or connected to each other by either Z-value or delta-Z-value.

Thus, objects located within layers also move when the layer's Z-axis value is changed. Then, their relative position to objects on other layers is also changed.

Contrary to Revit and ArchiCAD, the VW system is non-prescriptive. It always has been. That is because the modeling functionality of VW/MiniCAD pre-dates the architectural/BIM functions. Think of the architectural tools as functional overlays to a generic modeling/drawing environment.

Being non-prescriptive, the user has the flexibility to determine, or refine suggested "best practice", the methodology of implementing the coordinate system in a hybrid 2D/3D environment.

The slab layer contains whatever you want it to contain, or not. The relationship of objects in that layer spatial container in the Z-axis are always connected to each other, but not objects on other layer.

The floor "system" can be as nebulous or as detailed as you want. It could be as simple as a Floor object that is drawn as 24" thick and the top at the layer's internal Z=0" (or as the current case may be, the bottom of the slab is at -24" and is 24" thick...don't ask, it is just the way it is for now). The floor system could be an assembly that has a Floor object 1-1/8" thick with framing located beneath. One user may put the sheathing below on this layer, but another user may put it on the Mod-Floor-? layer below. The point is, it is arbitrary. The architectural modeling tools have certain "best practices" as I've tried to demonstrate in the BIM in Practice files.

The stairs in Alexandria Lofts were setup on the Slab layers to demonstrate the use of setting the height of the stair by layers. That is, the stair's height is determined by the Z-value of the layers it is spanning between. Due to a bug, I was unable to get this working properly (hopefully soon to be fixed). But, the stair also works on the Slab layer graphically, in the way it stacks below the edges of walls and aligns with the openings of the floor it is implicitly connected to.

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