One of the first places you'll encounter sketch-based modeling is with the Floor and Roof tools. When you initiate either of these tools, you are instantly placed in Sketch mode. The Ribbon changes, indicating the new mode (Figure 6.3), and you see a set of tools specific to the task of creating 2D sketch lines and creating lines with relationships to other model elements.

Figure 6.3. The Create Floor Boundary tab offers tools for sketching the floor shape.

For example, you can either draw lines freely using the Line tool in Draw panel, or use the Pick Walls tool from the same panel, which generates the floor or roof sketch lines when you pick on walls. When using the pick walls method, you create an explicit relationship between the floor or roof sketch and the walls. As a result, when walls move, the sketch (and thus the floor or the roof made of it) adapts and updates with the walls.

There are a few important rules you must apply when creating a sketch so that it is valid:

If you were to draw another loop within those openings, it would be positive and create another solid piece of floor of the same type. Here's the logic behind loops: one is positive, the next one within it is negative, and the next one within it is positive (Figure 6.5).

Figure 6.5. An additional loop of lines results in a positive shape.

Here are some rules of thumb you will need to follow when sketching:

The work plane is a 3D plane that you sketch on. For example, when you are in a plan view and start sketching a floor, the work plane is set to the level associated with the plan view you are working in. The majority of views in Revit (plans, 3D views, or views set in the family templates) have predefined work planes set automatically when they are created. Views such as sections and elevations require you to manually pick a work plane in order to add 3D elements to those views. In some cases, as with placing windows or doors in an elevation view, this is done implicitly—the cursor locates planes (walls) automatically.

A work plane can be understood as a surface on which you draw or place something. Imagine you are holding a marker in your hand and have a space in front of you. Can you draw with the marker in the space? No. You need a piece of paper, glass, wall—some kind of a surface to draw on. So, a work plane defines a surface on which you can build geometry. You can define a work plane by drawing a reference plane, picking a face from an existing element, or using an existing level (datum) as a reference.

Figure 6.6 illustrates the work plane. There are a few simple rules you must follow when using a work plane:

Figure 6.6. Concept of work planes.

Let's take a closer look at the types of work planes available in Revit.

Levels are horizontal work planes that define the levels in a building and can also be used to denote important horizontal references in a building (such as attic height). Levels are only created and visible in section or elevation views. The only exception to this is when creating a new Conceptual Mass in the Family Editor—there levels are represented in a 3D view. Each level typically has a corresponding floor plan view associated with it, although it is possible to make levels with no associated floor plan. For example, a level may define the Top of Steel in a building section, but there is no need to have a floor plan view of that level. For that case, you can create levels without plans by clearing the option Make Plan View on the Options bar when the Level tool is activated. This creates a level that appears black and white rather than blue, indicating that there is no hyperlinked view.

Note that when you create new levels using the Copy tool from the Modify panel, the newly created levels are black and white (unlike the levels that are drawn using the Level tool and that are represented with a blue symbol). This change in color indicates that this level has not generated a new floor plan that is associated with that level as the Level tool does usually. If you do need a corresponding floor plan associated with that level, you can use the Plan Views tool in the Create panel of the View tab. You will then be able to add a plan view associated with any existing level in the project.

When you place families, they automatically become associated with the level they are placed on. Walls, roofs, and stairs all have top and bottom constraints to levels. This guarantees that when the level changes height, so too will all the elements on that level. All sketch-based families such as floors, roofs, ceilings, and stairs are also associated with at least one level. This, however, means as well that if you delete a level, all the elements associated with that level will also be deleted! So use caution when deleting levels; it's not just a drawing that you are deleting!

Grids are vertical planes used as standard references in the construction industry for creating location grids on the site as well as a communication reference between the building participants. These construction datums are used to accurately define locations for elements such as columns and beams or positions of main structural walls or the exterior shell. You can associate elements with the grids so that when the grid system changes, it controls the position of the associated elements. A good example for that would be columns associated with grid intersections. As with a level, when a grid is moved, associated elements move with the grid (Figure 6.7). Grids and levels (datum) only show up in views that intersect the datum.

Figure 6.7. Grids are reference planes that can be used to control other elements such as beams and columns.

Reference planes are used to drive other geometry. They are planes that exist in 3D space that other elements can be attached to. While not visible in 3D views, they can be seen when perpendicular to plan, section, and elevations and are represented as green dashed lines. Similar to levels and grids, these lines are not view specific and will appear in all perpendicular plans, sections, and elevations. Even though reference planes look and feel like ordinary lines, they are very different. Think of them as symbolic representations of infinite planes. The ends of reference planes are selectable and you can drag them to make them longer, but you will not be able to rotate the end of a reference plane freely as you can with lines.

Using Reference Planes in the Family Editor

Reference planes are the essence of parametric content creation in the Family Editor, as they are used to create the parametric skeleton to which geometry is then attached and allowed to vary. The reference planes in a family are what you dimension to when they are loaded into a project—not the geometry.

Giving the reference planes various states also affects how other elements relate to the family. A reference plane can be set as not a reference, weak, or strong, and it can be defined as a reference for the left, right, front, bottom, back, or center position. The selection of these options is important in the Family Editor environment, as they define references for snapping. When you have two crossing references set as Strong, they define the insertion point of an element when you place it in the project environment. The origin must be further defined in the instance properties of the crossing reference planes by selecting "Defines Origin."

In Figure 6.8, the two centrally positioned strong references define the insertion point of the element. The weak references serve only as secondary snaps.

Figure 6.8. The insertion point of the desk is the point of the two crossing references that has been identified as "Defines Origin."

In a project, reference planes can be used to drive geometry (see Figure 6.9).

Figure 6.9. Reference planes are used extensively in the Family Editor to create parametric constraints that can drive forms and define snapping references. In this example, two of the vertical reference planes define the width of the chair while the two horizontal define its height.

Reference lines were designed mostly for use in the Family Editor to overcome the limitation of the reference planes and their inability to define constraints that reference a point, direction, and angle. Unlike with reference planes, the start and end points of a reference line can be referenced and used for dimensioning. A popular use of a reference line is to define door swing opening angles by creating an angular relationship between the door leaf position and the closed state of the door leaf. This will let the user set any angle of door opening later in the project. Other differences between reference lines and reference planes are that you cannot name the reference lines and you can only select them graphically.

Reference lines define four work planes—the two along the axis of the reference line and the third and fourth planes that are perpendicular to each of the line segments (see Figure 6.10).

Figure 6.10. Reference lines are used to control door swings and opening angle in families.

Scope Boxes

As previously mentioned, reference planes extend in all views. Once drawn in one view, they will appear in every view that shows the area where they are created. But that is not necessarily what you always need. Let's say your project has a base of five floors of conference area with a 30-story hotel above (like the model shown in Figure 6.11). It's likely you'll have separate structural bays for each part of the building. You don't need to see all grid lines of the conferencing base in the hotel tower, and vice versa.

Figure 6.11. (A) This building consists of two main volumes, a low volume with conference usage and a tower with hotel use. These two volumes use separate grid systems, and thus two different scope boxes are created to control the visibility of the separate grids. (B) Grid element properties indicate the scope box to which the grid belongs.

The Scope Box tool will help you deal with this issue and allow you to limit the range in which reference planes (grid lines, levels, and reference lines) extend and appear. In our example shown in Figure 6.11, the building has a base shape that accommodates a conference center and a tower in which a hotel is situated. They have very different configurations and need different grid systems. The thing to do is to draw two separate scope boxes around those two entities, using the Scope Box tool allocated in the Create panel of the View menu. Then the grids of each of those two parts of the building need to be assigned to the appropriate scope box (the grid of the base to the Conference scope box and the grid of the tower to the Hotel scope box).

Scope boxes are visible in 3D views—although not in camera (perspective) views—and you can easily manipulate their extents at any time directly using the grip controls. Assigning gridlines or other datums to a scope box is easy: select the gridlines, and in the Instance Properties dialog box, choose the Scope Box parameter and select the scope box where the datums should belong. Figure 6.11 shows the Instance Properties dialog box for the gridlines and the associated scope box.

Visibility of Grid Lines in Sections and Elevations

Grid lines will show in section or elevation view and only if the view is cut perpendicular to the grid line. In no other case will the grid line appear. This is done to avoid confusion on the construction site due to misleading graphic description.

Before moving on to look at using work planes in practice, let's take a moment to summarize the basic theory.

Working with Work Planes

Figure 6.12. The Work Plane dialog box lets you specify the active work plane for a view.

Name

This option displays available levels, grids, and named reference planes. Note that only reference planes to which you have explicitly assigned names appear in this list. To name a reference plane, use the element properties of the reference plane.

Pick a Plane

This option allows you to select a plane interactively in the model. The selection is visual and you need to click on a reference plane, wall face, or faces of an element. Figure 6.13 shows how different an extruded shape will be when selecting different planes on which to sketch and create a void extrusion. The face of the element that's marked darker represents which side of the element was set as a work plane.

Figure 6.13. The same mass and the same 2D shape extruded as a hole. In (A) the extrusion shape is drawn on the front face of the mass; in (B) the extrusion is drawn on the back face of the mass.

Pick a Line and Use the Work Plane It Was Sketched In

With this option, Revit converts the work plane on which the line was created into the active work plane. When you select a work plane that is perpendicular to your current view, Revit opens a new Go to View dialog box that gives you options to select a view in which the chosen work plane can be worked on (Figure 6.14).

Figure 6.14. The Go to View dialog box lists views where you can work on the active work plane.

Work Plane Visibility

If you are not sure where your active work plane is, click the Show button in the Work Plane panel.

Other Work Plane Operations

Revit will let you rotate a work plane grid by clicking on it and selecting Rotate from the Modify panel. This in turn affects how new elements will be placed on that work plane. You can also align elements to the work plane grid, and lines will snap to the grid (Figure 6.16).

Figure 6.15. Making the work plane visible helps you understand the active work plane in a 3D view.

Figure 6.16. When the work plane grid is rotated, new elements placed on the work plane will also be rotated.

To change the work plane an element is already associated with, select the element, and then click the Edit Work Plane button in the Work Plane panel of the Modify tab and select another work plane using one of the methods in the dialog box.

To dissociate an element from a work plane, first select the element. Next, click the Edit Work Plane button in the Work Plane panel to display the dialog box shown in Figure 6.17, and click the Dissociate button. The element will then be free to move anywhere in the model. Note that this option is only available for work plane-based families.

Figure 6.17. The Work Plane dialog box allows you to set the work plane of an element or dissociate it from its work plane.

Once you have dissociated an element from its work plane, you will notice that the value for the work plane instance parameter (located in Element Properties) will be set to <not associated>.

Most importantly, you will notice that the element is free from constraints and is free to be moved in any 3D direction.

To rehost elements from one host (wall, floor, or roof, for example) to another, you can use the Pick New Host button from the same Work Plane panel when an element is selected. This allows you to select a new host to place the element. With this tool, you can choose any new host—it does not have to be in the same plane as the original. For example, you can select a window in one wall, click the Pick New Host button, and then choose a new wall for the window.

Figure 6.18 shows an extruded shape originally created on a horizontal work plane. Using the Pick New Host tool, you can place the form on any surface in the model.

Figure 6.18. (A) Original condition; (B) desired repositioning of the curved element; (C) the element is rehosted and a relationship between the two elements has been created; (D) the host changed its geometry and the hosted elements follow the change.

Real World Scenario: Using Work Planes with Revit Roofs

Here are two versions of the same building, with roofs that use the same sketch profile but are drawn on two different work planes. Image A shows a roof by extrusion sketched on a work plane parallel to the exterior wall; B shows the same roof sketched on a work plane rotated 45 degrees with respect to the exterior wall. Notice the difference!

Creating a Roof by Extrusion (Default Work Plane)

Take the following steps to see for yourself how version A was created:

1. Draw four walls in plan view in the shape of a square.

2. On the Work Plane panel of the Home tab, select the Reference Plane tool and draw a reference plane parallel to the south wall:

   

3. Pick the reference plane and open its instance properties. Give it the name Front Roof Plane.

4. On the Create panel of the Home tab, select the Roof tool and select Roof by Extrusion. You will be prompted to select a work plane.

   

5. From the Name list, select the named reference plane you just drew and named. You'll be asked to open a view to begin sketching. Choose the south elevation.

6. Sketch a roof in arc shape, as shown here, and finish the sketch:

   

7. Go to the default 3D view and, using the blue arrows, adjust the length of the roof to make sure it extends beyond the exterior walls, as shown here:

   

8. While still in the 3D view, select all the walls. Click the Top/Base: Attach button in the Modify Walls panel of the Modify tab and then select the roof to attach the walls to the roof. The resulting building should look something like this:

   

9. To cut the roof so that it ends at the edge of the exterior walls, switch to plan view (Level 2 or Site plan), select the roof, and select the option Vertical Opening in the Modify Roof panel. This allows you to cut off the extruded roof exactly at the edge of the building, regardless of its shape. In this example, draw two rectangles (the location is indicated in the following figure with Vertical opening) that cut the roof up to the face of the walls.

   

   After applying the two sketches using the Vertical Opening tool, the final result for the first roof should look like this:

   

Creating Version B: A Roof Using a 45-Degree Work Plane as a Reference

To obtain the second roof (B) shown at the beginning of this section, repeat all the previous steps, but draw the reference plane at a 45-degree angle to the building, as shown here. Remember to give the reference plane a different name in its Instance Properties dialog box.

The finished roof looks like this: