A guide to modeling on top of a surface.
Now that you’ve familiarized yourself with the tools in the ribbon, configured your Quick Access Toolbar, assigned your keyboard shortcuts and experimented with the snaps in Part 3 of this series, it’s time to gear yourself up for modeling, starting with work planes.

In the 3D world, the work plane is the surface where 3D elements are created and where 2D lines are sketched. Any element modeled in Revit requires a work plane. When the Show button is clicked from the Create > Work Plane of the Family Editor (see Figure 1), the active work plane is represented by a light blue surface as shown in Figure 2.

In the Project Browser > Views of a project, work planes are referred to as Level 1, Level 2 and Site (see Figure 3). Additional levels can also be added.

In the Project Browser > Views of the Family Editor, the default work plane is referred to as the Ref. Level (reference level), as shown in Figure 4.
Thereafter, when the family is loaded into a project, you have the option to associate its base location (the Ref. Level) with a specific level. Your other options are as follows:
- Accept the default base location of the family in the level as it is brought into the project. In most cases, the family will be sitting on top of the Ref. Level work plane. After loading the family into the project, it will rest on top of the level’s work plane.
- After loading the family in a project, enter a value in the Constraints > Offset field of the Properties palette (see Figure 5) or leave it at 0′ 0″.
- Enter a value in a specific field in the Properties palette if the family is parametric and was created with an offset parameter. In Figure 6, the family was created with an instance parameter named Dist. from Floor.

The Reference Planes
These are the green dashed lines you see in a project. They are used for locating walls or aligning objects. In the family editor, reference planes are used mainly as construction lines—sort of like sketch or guide lines that can be left in a view or hidden with the Hide Element command (see Figure 7).

When creating a new family using the Generic Model template, two pinned reference planes are shown in the Ref. Level view by default (see Figure 8). When the cursor hovers on top of the vertical reference plane, it is named Center (Left/Right) while the horizontal reference plane is named Center (Front/Back).

Their intersection corresponds to the tip of the cursor when a family is being placed in the plan view of a project (see Figure 9).

The length of a reference plane is infinite and has no start or end points. What is being drawn is a symbolic representation of an infinite plane. It is initially used for sketching the general shape of a family. After laying them out, it is much easier to draw numerous components derived from extrusion, sweep, blend and revolve tools (see Figure 10).

While in a sketch mode (or after finishing the sketch), a line in an extrusion can be locked with the reference plane it’s on top of by using the align tool to click both lines and then clicking the lock icon (see Figure 11).

This locking process is the first step when you want to create a parametric family. Reference planes are used to drive geometry attached to them. When a dimension is added between reference planes and labeled, parameters can be assigned, including height, width and length (see Figure 12).

Therefore, when the value of a parameter is changed, the component and the reference plane adjust accordingly (see Figure 13).

Note: Parameters will be discussed in Part 7 of this series.
When a reference plane is named, it automatically becomes a work plane (e.g. top of cylinder). This named reference plane is added to the Name drop-down list from the Work Plane dialog box (see Figure 14), which is accessed by clicking the Set button (Create > Work Plane).