AUTODESK REVIT BUILDING INFORMATION MODELING
Best Practices for Autodesk Revit Parametric Components
(Families)Autodesk Revit Parametric Components (also referred to as
Families) offer an open, graphical system for design thinking and
form making. A powerful feature in the Revit suite of products,
families help users manage data and make changes easily. This white
paper examines Best Practices relating to Autodesk Revit
Families.Revit Parametric Components are called families because
one family type can contain many variations. A family can be
anything in Autodesk Revit software, from a table to a window to a
two-dimensional representation of an anchor bolt. Any item that may
need to be represented in a project can be created in a family. A
large number of predefined families are included with Revit.
Manufacturers are creating Autodesk Revit Families that are
available from their websites or included on product disks. Despite
the availability of large family libraries, users sometimes need to
create custom components for a project. This can be easily
accomplished using the Autodesk Revit Family Editor; a simple
graphical interface that allows users to model any object and apply
the power of parametrics to that object. Users do not need to know
any programming language to create content for Autodesk Revit.
Family creation is made easy through the use of templates, which
are provided with the software to help users get started with
families. These templates allow Revit users to focus on the
geometry of the object, as they contain all the programming
necessary behind the scene. Autodesk Revit Families are extremely
powerful because they are driven by the Revit parametric change
engine. The parametric change engine enables a change made to a
family to propagate throughout the entire project. Once created, a
familys parameters remain exposed and can be edited directly within
the Revit project. Ultimately, it is the parameters that drive a
familys geometry. Mathematical formulas can be used in these
parameters to create complicated geometry, or to drive parameters
in a user defined solution (for example, using a formula in a
window family that always makes the width of the window twice its
height). Revit Families also feature nested families - one family
residing in another family. For example, a user might nest a door
hardware family into a door family. Nested families add a level of
strength and capacity to the process. Users can create a single
family file that includes dozens of different options.
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Best Practices for Autodesk Revit Parametric Components
(Families)
This paper explores the use of families in Autodesk Revit - from
the basics of the Family Editor to advanced topics and
considerations when using families - all of which will provide the
reader with a Best Practices approach to creating parametric
component families in Revit.
Design ConsiderationsBefore creating a family in Revit, users
should consider the following questions regarding their intended
use of a family: What size(s) does this family come in? Is this a
custom piece of furniture that only comes in one configuration, or
is this a window that is available in several preset sizes?
Perhaps, this is a bookshelf that can be built in any length from
between 2-0 to 5-0 wide. This is an important point to consider
before building a family, as it will dictate decisions that need to
be made in the near future. How should this family appear in
different views? Is this an object that should be seen from plan
view, elevation view, and/or sectional views? Maybe this is a 2D
object that should only be seen in plan or elevation. In any case,
the way that this object should appear in views will determine how
to define its visibility. Does this family require a host? Is this
family typically attached to another design element - a wall, or
maybe a ceiling? Possibly it is a roof mounted mechanical unit. How
this family is hosted (or what it does or does not attach to) will
determine which template file should be used to start the family.
How much detail should be modeled? Is this family an electrical
wall outlet that will only be seen in interior elevations from a
distance, or is it a door family with raised panels and a sidelight
that will be seen in an interior rendering of the project? This
determination will help decide how much detail to provide in the
family. Where should the origin point be? Is this a column family
that would use the center of the circular base as the insertion
point, or is this an accessible toilet that must always be placed
18 inches off the adjacent wall to meet code? This decision will
help users when they start placing geometry. Recapping these
important first questions to consider before creating a family: 1.
2. 3. 4. 5. What sizes does the family come in? How does this
family appear in different views? What hosts might this family be
attached to? How detailed should this family be? What is the origin
point of this family?
Creating a New FamilyOnce the basic questions listed above are
considered, a user is ready to create a new family. There are three
types of Autodesk Revit families: System families, In-place
families, and Standard component families.
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Best Practices for Autodesk Revit Parametric Components
(Families)
System families are predefined within Autodesk Revit, and
comprise the basic building components such as walls, floors, and
roofs. Users can create their own versions of system families by
duplicating an existing version and modifying its properties. Users
cannot create new system families. In-place families are components
that are created specifically for a single project only. They are
created from within the current project, and cannot be used in
other concurrent or future projects. The best time to use an
in-place family over a standard component family is when creating a
component unique to a specific project. For instance: a reception
desk in the lobby of a law firm may have a very unique design
featuring curving shapes requested by the client and finishes
unique to that lobby. In this situation, an in-place family should
be used because there is little chance that this custom-designed
piece will be repeated in another project. Standard component
families are the most common families in Autodesk Revit, and are
the focus of the remainder of this paper. Standard component
families can be placed in project template files so that they
preload with each new project, or they can reside in libraries to
be loaded on demand. While working in the Family Editor, users can:
1) open an existing family and modify it to suit their needs, or 2)
start a new family using the appropriate template. To start a new
family, choose the File pull down menu and then select New >>
Family.
TIP: To save time, users should duplicate and modify a similar
existing family to suit their needs instead of starting a new
family from a template.
TemplatesTemplates for family creation are supplied with
Autodesk Revit. The various templates cover a broad range of
possibilities from 2D annotation objects to 3D roof-based spot
lights. Each template has been pre-configured to aid in the
construction of a specific object type.
Figure 1 Autodesk Revit includes many templates to create
families of parametric components.
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Best Practices for Autodesk Revit Parametric Components
(Families)
Some templates have a combination of reference planes and
pre-defined parameters to guide users during creation. Family
templates for hosted objects will contain a host to build from. For
example, in roof-based families a portion of a roof will be exposed
in the template for the user to reference as a base. Still other
templates have text notes embedded in them that may define the
interior and exterior faces of a wall. Another item that is found
in some family templates are controls. Controls placed in families
allow the user to change the position of the geometry in a family
after its loaded into the project. An example of these controls can
be seen in a door family, where controls allow the swing and the
hinge-side of the door to be reversed.
Figure 2 The template for a door family includes controls to
easily reverse the swing and hinge-side of the door..
To create a family based on a template, browse the list of
templates, and choose the one most appropriate to the object being
built. If the object does not fall into a specific category, the
Generic Model template may be the best choice. After picking the
template, the user is ready to launch the Family Editor.
Family EditorThe Family Editor is built into Revit, and is
launched by opening an existing family (those with an RFA
extension) or by starting a new family from within Revit. The
Family Editor launches within the Revit application, and employs
the same user interface. The Design Bar on the left of the drawing
window changes to a unique set of tools for family creation, and
the Project Browser updates to show specific views depending on
template selection.
Figure 3 The Family Editor user interface matches the general
Revit user interface.
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Best Practices for Autodesk Revit Parametric Components
(Families)
At a minimum, the drawing window will display two crossing
Reference Planes - and possibly some dimensions, text, and notes to
the designer. The crossing Reference Planes are important because
they define the origin of the family. Its a Revit Best Practice to
leave these existing items (preloaded from the family template)
alone. Users should not move or delete these items, as they play an
important role in the family. In fact, there are some items (such
as dimensions) in some family templates that cannot be deleted by
the user - underscoring the general principal that if an item is in
the template when it's first opened, it should be left there.
Reference PlanesA common mistake among users is to start adding
objects and solids at this point. While its almost time to start
modeling, there is still some more preparation that will later
serve a significant purpose. After opening the template, the first
thing a user should do - before creating model geometry - is use
Reference Planes and Reference Lines to create construction lines
for the geometry that will be added later. Start in a view that
best fits the family being created, such as a plan or elevation.
Reference Planes should be used as datum lines that extend beyond
the edges of the visible drawing area. Drawing a reference plane
(often called ref planes) in a plan view will also cause that same
reference plane to be seen in a crossing elevation or section view,
because it is literally a plane that extends in a horizontal and
vertical direction simultaneously.
Figure 4 Reference Planes should be defined before creating
geometry.
Unlike reference lines, reference planes do not have defined
endpoints. They consist of two associated planes: one parallel to
the view and one perpendicular. Ref Lines can be used in rotational
control of families, because the endpoint can be constrained.
Reference Lines and Planes can be renamed, so that users can easily
refer to them at another time.
Creating ParametersReference planes that have been laid out
should align with the major axes of the planned geometry. Users
should begin to add dimensions to specify parametric component
geometry. Start by thinking how the object should be controlled.
Height, width, and depth are three dimensions often used in
families, and these dimensions and parameters are pre-loaded with
many of the templates. Users may need to add more dimensions to
describe other geometry for instance; trim, width, and depth are
common in a Window family.
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Best Practices for Autodesk Revit Parametric Components
(Families)
Once the dimensions have been added for the major pieces, users
can start adding labels to dimensions, creating parameters. There
are two categories of parameters: instance parameters and type
parameters. Changing an instance parameter affects the parameters
of a single entity (or instance) of an object. Changing a type
parameter affects all parameters of the same type. If there are
several instances of the same family loaded into a project, and
each individual representation of that family needs to be a
different length, then use instance parameters. For example,
consider two counter tops in the same project. One instance of the
counter top is placed and its length (an instance parameter) is set
to 5 0. A second counter top is placed and its length (an instance
parameter) is set to 5 5 , spanning the distance between two walls.
The instance parameters easily allow these two counter tops to be
set to different lengths. Instance parameters have another unique
characteristic: dimensions that are controlled by instance
parameters will display shape handles when selected in a Revit
project. Shape handles allow the user to click and stretch the
shape of a family to a new position or size by using the mouse.
Figure 5 Instance parameters display shape handles (shown here in
blue), a convenient way to stretch the shape of a family.
Type parameters control families at a higher level. They control
the predefined types of families used in the project. Use type
parameters to load an object repeatedly in a project and control
those repeated objects as if they were one. For example, consider a
door family. A users places a door repeatedly in the model as a 6-8
tall door, but later decides to change the height of all the doors
to 7-0. Changing one type parameter will cause all of these doors
to update their height simultaneously. To add a parameter, click on
a dimension then add a label. Once the dimension is labeled, it
becomes a parameter. In the Options Bar, a drop down list of
available parameters will appear. If the parameter needed is not
available, select Add Parameter. When adding a new parameter,
specify whether it's an instance or type parameter. After adding
the parameter, the dimension changes to include the parameter name
and the dimensional length.
Figure 6 Add a new parameter using the Revit Family editor.
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Best Practices for Autodesk Revit Parametric Components
(Families)
As parameters are created, they are added to the parameter list
in the Family Types dialogue box (selecting by clicking Family
Types in the Design Bar). This Family Types dialogue box contains
several key areas. Most noticeable is the list of defined
parameters in the main window, arranged into logical parameter
groups (Construction, Dimensions, and Identity Data in the example
in Figure 7). During creation or editing, users can assign which
category is assigned to a parameter.
Figure 7 Family parameters are listed in the Family Types dialog
box.
On the right side of the dialog box, users can create new Family
Types, or rename or delete existing Family Types. Revit features
Family Types to predefine a set of parameters - making a particular
type of object. Returning to the door family as an example, several
door types can be defined in this dialog box. One type might be a
3068 door (a door that is 30 wide and 6-8 tall). Another type might
be a 3668 (36 wide and 6-8 tall). A user could then define a 3070
and a 3670 door in this dialog box. Family Types allow Revit users
to quickly define a multitude of sizes and combinations of an
object, based on just one family and one set of parameters. The
lower group of three buttons in the Family Types dialog box is
specifically for parameter creation; Add, Modify, and Remove. Click
the Add button to launch the Parameter Properties dialog box to add
a parameter to this family. Notice the Parameter Types section of
this Parameter Properties dialog box (see Figure 8). There are two
types of parameters available in Revit: family parameters and
shared parameters. A family parameter is specific only to this
particular object and its value cannot appear in a schedule or tag.
A shared parameter can be shared across multiple families and
projects. Its value can appear in schedules and tags, and can also
be exported out to ODBC. Family parameters are stored within the
family file, whereas shared parameters are saved in an external
text (TXT) file, typically on a network where other users can
access the text file to use the shared parameters.
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Best Practices for Autodesk Revit Parametric Components
(Families)
Figure 8 Family parameters are listed in the Family Types dialog
box.
Parameter data for a family parameter is entered in the
Parameter Properties dialog box.: Name: The parameter's name is
completely left to the user. Its a Revit Best Practice to keep
these names simple, short, and concise whenever possible. When
using formulas (described later in this paper), these parameter
names will have to be retyped exactly as entered here. Discipline:
A parameter's discipline can be set to Common or Structural. Type:
This drop-down list contains several pre-defined categories for the
value of the parameter, such as Text or Number, or Yes/No. Group
Parameter Under: This area allows users to classify the parameter
in a logical grouping. When the family appears in a project, the
parameters are listed in groups of common elements to make it
easier to enter the data by logical groups. Instance and Type.
Select the radio buttons that best fits the parameter. Once these
decisions regarding a parameter are made, enter the necessary data
into the fields in this dialog box, and click the OK button, which
returns the user to the Family Types dialog box. The user will now
see the new parameter listed under the Parameters heading, and
organized into the groups defined in the previous step. To change
the parameter, users can click the Modify button, or remove the
parameter from the family entirely with the Remove button. Continue
to add additional parameters by repeating the steps above to
complete the design of the family.
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Best Practices for Autodesk Revit Parametric Components
(Families)
Testing the FamilyBefore finishing a family, its very important
to "flex" or test the model - to check that the elements created
are reacting as expected when parameters change. Users should
develop a habit of flexing the model repeatedly when creating
families, especially after adding parameters. To flex the model,
click the Family Types button in the Design Bar. In the Family
Types dialog box, the various parameters of the object are listed.
Pick a parameter, and change the dimension value associated with
it, then click Apply and see how the model changes. The intention
is to see if the reference planes have moved to a new position as
expected. Change the parameters to a range of numbers (clicking
Apply each time) to test a range of values from which the family
would normally operate - to assure the planes are moving to the
correct lengths and dimensions. Occasionally a user will see an
error such as Constraints not Satisfied. This usually means that
the parameter is trying to control a part that is already
constrained by another parameter. As more parameters are added to
the model, be sure to flex multiple parameters to test them. For
instance, if flexing the width works well, then set a new width,
and flex the height. Try different combinations to assure all is
moving as expected. Once a user is satisfied that reference planes,
dimensions, and parameters are all working as expected, it's
finally time to add some real geometry in the form of Solids and
Voids.
TIP: When flexing the model, move the dialog box to the side of
the screen, to better see the family in the drawing area.
Adding GeometryThere are several choices for creating geometry
in Revit: Extrusions, Blends, Sweeps, and Revolves. These four
geometry types can either be solids or voids. The type of geometry
used depends on what is being modeled. For example, in a door
family, the door panel itself could be an extrusion of a
rectangular shape. The door frame could be a sweep - a profile in
the shape of the door frame would be swept along a path defined by
the sides and top of the door opening. The door knob might be a
revolve. A void-blend could be used to cut the raised panel into
the surface of the door panel. The method for adding geometry is
similar for all geometry types. The rest of this section will use
extrusions as an example. From the Design Bar in the Family editor,
choose Solid, then Extrusion. Revit will switch to Sketch Mode, and
the user will have two options for sketching a shape. The first
option is to draw the shape using tools from the Options Bar such
as Line, Arc, Circle, Polygon, etc. The second option is to use the
Pick tool from the Options Bar to pick reference planes, lines, or
other existing geometry. As the user begins to draw or pick,
magenta sketch lines appear. These lines could be drawn over the
top of the reference planes, or more loosely sketched and then
moved into alignment with the reference planes. The key is to make
these sketch lines lock to the reference planes. Using the Pick
tool, the user has the option to lock the sketch lines upon
placement. Blue padlock symbols will appear when lines can be
locked to other geometry, lines, or reference planes. To lock and
unlock relationships, simply click the lock symbol to toggle it
opened (unlocked) and closed (locked). Sketch lines can be moved
using a 'press and drag' technique; clicking on the line and moving
the mouse while holding down the mouse button. When using this
method, notice that sketch lines will automatically snap to
reference planes and other relationships while being moved. Moving
a sketch line off and back onto a reference plane will cause the
lock symbol to appear, allowing the user to choose to lock it or
not. The Align tool also allows the user to create constraints
using the lock symbols. After sketching the shape, and locking the
sketch to the appropriate reference planes, the Extrusion
properties in the Design Bar are used to define the thickness of
the extrusion. This
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Best Practices for Autodesk Revit Parametric Components
(Families)
number can also be set in the Options Bar. When satisfied, click
Finish Sketch and the geometry will appear. Flex the model again
from various views, including 3D, to make sure the geometry behaves
as expected. If it doesnt, highlight the geometry and stretch it,
using the blue shape handles that appear, to align and constrain to
a reference plane.
FormulasFormulas are one of the many powerful aspects of Revit
Families - used to control families in a variety of ways. Formulas
can use logic such as IF statements (IF the width is 1-0, set the
height to 4-0) as well as mathematical expressions. They can be
used to control Yes/No parameters, and to control parametric
arrays. Formulas are typed directly into the Family Types dialog
box, where all of the parameters for a family are listed. Simply
place a formula into the cell adjacent to the value, beginning with
an equal sign. When entering a formula, abbreviations (such as +, ,
sin, and so forth) can be used.
*
TIP: The following are valid formula abbreviations: + * / ^ log
sqrt sin cos tan asin acos atan exp abs Addition Subtraction
Multiplication Division Exponentiation, i.e. x^y = x raised to the
power of y Logarithm Square root, i.e. sqrt(16) Sine Cosine Tangent
Arcsine Arccosine Arctangent e raised to an x power Absolute
Value
Referring back to the family parameters listed in the Family
Types dialog box in Figure 7, notice that there are parameters for
height and width. In the figure, the height = 4-0 and width = 3-0.
To set the width of this family to always be one half the height,
click in the Formula column of the width parameter and enter
=Height/2. The values are case sensitive, and must be typed exactly
as they are defined. This is why it is important, when naming
parameters, to be concise about the name chosen (as described above
in the Creating Parameters section). Test how formulas work by
changing the value of height, and watching the width value change
automatically. There are many complex mathematical functions that
can be used. Logical functions include IF, AND, OR, and NOT
statements. Formulas can also use greater than/less than signs
(< >). Experimenting with formulas will allow users to create
some very powerful Revit Families, such as a book shelf that
automatically adds support brackets as the length of the shelf
increases or a window family where the muntins turn off when the
window size decreases beyond a defined limit.
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Best Practices for Autodesk Revit Parametric Components
(Families)
Saving a Revit FamilyWhen the Revit Family is ready to be used
in a project, save the family with an appropriate name, and store
it in a location that is easy to find. A Best Practices tip is to
organize family content into a system that mimics the Revit
Library. This makes it much easier for users to find what they're
looking for. To load the family into a project, select File
>> Load From Library >> Load Family, and then browse to
the saved file and select it. Alternately, for many component
types, when the tool is selected, a Load button becomes active in
the Design Bar.
TIP: Create a keyboard shortcut to automatically open the Load
Family dialog box, or click the Load button in the Options Bar for
many component types such as doors and windows when the tool is
selected in the Design Bar.
Once loaded into a project, the family can be moved and copied
as needed. To edit the family, simply select the object, and click
the Edit Family button in the Options Bar. This will launch the
Family Editor and open the selected family. When finished editing,
the family can be loaded directly back into the project by clicking
the Load into Project button in the Design Bar. Saving the family
from the Family Editor using this method will overwrite the file
that was originally the source for the object in the project.
Simply modifying and reloading without saving will update ONLY the
project into which the family is loaded.
TIP: There are many resources available if users need assistance
or are have problems with Autodesk Revit families. First, file a
Support Request through the Help Menu in Revit. This puts users
directly in touch with the Autodesk Revit team for assistance. The
Revit Forums at AUGI.com are also an invaluable resource.
Membership is free and there are thousands of people from around
the world logged in 24 hours a day - ready and willing to help.
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Best Practices for Autodesk Revit Parametric Components
(Families)
Final Review Steps to create a family in Autodesk Revit: 1. 2.
3. 4. 5. 6. 7. 8. 9. Select the appropriate family template. Lay
out reference planes to aid in drawing component geometry. Add
dimensions to specify parametric component geometry. Add labels to
dimensions to create type or instance parameters. Flex the new
model to verify correct component behavior. Add geometry in Solids
and Voids, locked to reference planes. Specify 2D and 3D geometry
display characteristics with sub-category and entity visibility
settings. Define family type variations by specifying different
parameters. Save the newly-defined family, then load it into a new
project and see how it performs.
SummaryAutodesk Revit Families and the Family Editor are
extremely powerful. One of the best ways to become familiar with
the Family Editor is to open an existing family - investigate how
it was built and what parameters or formulas were used. Start by
watching the effect of changing parameters. After becoming
comfortable with existing families, try making a new family. Users
will soon come to realize and appreciate the full power of the
parametric technology inherent in Autodesk Revit.
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Best Practices for Autodesk Revit Parametric Components
(Families)
About Autodesk RevitThe Autodesk Revit platform is Autodesks
purpose-built solution for building information modeling.
Applications such as Autodesk Revit Building, Autodesk Revit
Structure, and Autodesk Revit Systems built on the Revit platform
are complete, discipline-specific building design and documentation
systems supporting all phases of design and construction
documentation. From conceptual studies through the most detailed
construction drawings and schedules, applications built on Revit
help provide immediate competitive advantage, better coordination
and quality, and can contribute to higher profitability for
architects and the rest of the building team. At the heart of the
Revit platform is the Revit parametric change engine, which
automatically coordinates changes made anywhere in model views or
drawing sheets, schedules, sections, plans you name it. For more
information about building information modeling please visit us at
http://www.autodesk.com/bim. For more information about Autodesk
Revit and the discipline-specific applications built on Revit
please visit us at http://www.autodesk.com/revit.
Autodesk and Revit are registered trademarks or trademarks of
Autodesk, Inc., in the USA and other countries. AUGI is a
registered trademark of Autodesk, Inc., licensed exclusively to the
Autodesk User Group International. All other brand names, product
names, or trademarks belong to their respective holders. Autodesk
reserves the right to alter product offerings and specifications at
any time without notice, and is not responsible for typographical
or graphical errors that may appear in this document. Computer
aided design software and other technical software products are
tools intended to be used by trained professionals and are not
substitutes for your professional judgment. 2006 Autodesk, Inc. All
rights reserved.
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