What Is a Family?
(And How Revit Courses Can Help You Understand This Basic BIM Concept)
If you spend any amount of time around users of the Autodesk Revit platform, you are sure to hear the term “family” used on a regular basis. Families are an integral part of the Revit toolkit, yet what they are and how they can be used is something that is often misunderstood. Whether you are new to the Revit software or have been using it for years, it is worth while to take a closer look at families and the part they play in your building information modeling (BIM). Revit courses are the fastest and most efficient way to learn Revit, but we have put together a primer on families in this article to get you started.
So What Exactly Is a Family?
A family contains the basic building blocks used to create an element in the Revit program. As you create (or “author”) families in Revit, you are authoring the code that goes into the elements you will use in your models. In simplistic terms, a family defines the geometry of an element, including its various parameters and the relationship of its geometry. This information is saved as a “family” and creates an element when it is inserted into a Revit model. But these families are also customizable. For instance, if you need the same element but in a different size, you can simply use the code within your original family to tell the element how to build a different-sized copy of itself.
How Do You Make a Family?
When you sit down to author a family, it is a good idea to already have a good idea of what you intend to make. It may be worthwhile drawing out on paper what your intended element should look like, and what geometry will be used to build it. Note what aspects are variable and which are static. Also make a note of what parameters will be used when creating the element, so that you can write this into your family.
When you are ready to dive into creating your family on Revit, the first thing to do is to choose a category and select a template. The category that you choose (such as door, window, furniture, etc.) will establish the basic behavior of your element. As an example, a door must be hosted by a wall (a door can’t exist on its own), while a column must extend between two levels. The category that you select will also define how the element is approached by the Revit platform in terms of visibility and scheduling.
Most categories only have one template per element, but a few have multiple options. Choose your template based on how you intend to use the element in your model.
Allowing for Variables
You will want some of your families to be flexible — for example, for the size to be adjustable, or to allow for moving parts. In this case, you will want to build a parametric family (one whose behavior is governed by parameters). To do so, you will need to create a framework through the use of reference lines and planes.
These planes are used to define all of the family’s important static and variable positions. The geometry that is authored for the family will be limited to the planes that are assigned, which means that this geometry will be governed by the movement of the planes.
Reference lines are used to put constraints on angles. For instance, if you need to input a constraint on how far a door can swing open, you would use a reference line. Otherwise, reference planes are preferable.
Governing Your Framework
Once you have created a framework, you can set up constraints in order to govern its use. This is done through the use of alignments and dimensions. Dimensions can be locked, established as “equal” or given a specific parameter so that you can govern the location of the reference plane within the framework you are writing.
As you establish constraints, you want to indicate both static and variable conditions. The variable (or flexible) conditions can change as you tweak the size of the element, while the static conditions will stay the same no matter what. For example, the width and length of a tabletop might be a flexible condition, allowing you to create larger or smaller tables. But the position of the legs relative to the rest of the table will remain static, and be governed by the width and length of the tabletop.
To ensure that you don’t run into snags down the line, it is a good idea to test your family once you are finished creating it. This is to say that once you have established a framework and assigned it certain constraints, it is a good idea to change the parameters (also called “flexing”) a few times to make sure that everything changes together as it should (i.e., that the constraints have been created correctly). Flexing families to test them when they are initially authored is a great way to save time down the road, as the last thing you want to do when putting together your model is have to re-author a faulty family.
It is also important to note that you don’t necessarily have to add any constraints to a family. If a family is intended to be completely static (i.e., not be changeable at all), then parameters are irrelevant. When you are first learning to author families, it might be a good idea to create a few without parametric constraints, just to keep things simple and easy as you get used to the process.
Giving Your Family Geometry
Once you have written your framework and constraints, the next step is to add geometry. The geometry is aligned to the framework, and constrained to it as well. In other words, as the flexible characteristics of the framework are tweaked, the geometry attached geometry will change with them. As you sketch onto the reference plains in your family’s framework, Revit will add automatically constrained sketch lines as it tries to understand and anticipate what your are doing. If you would like to be able to view the relationships of these lines in real time, you can go to the Visibility/Graphics Override box and activate automatic sketch dimensions.
It is important to be aware that you won’t be able to see any sketch lines that are constrained once the sketch is finished. While this shouldn’t affect your geometry, it can become a problem if you find you need to change the constraints or make other tweaks or corrections when flexing the family (as constraints in sketches can be difficult to find). An alternative to constraints created in a sketch is to create an additional set of reference planes to accomplish the same constraint. While this will take more time up front, it will make troubleshooting easier if you run into snags down the line.
Add More Frameworks
Once you have authored your first framework with all of its corresponding constraints and geometry, you can go on and repeat the process with any other frameworks that the family might require. With each new piece of geometry that is added, it is a good idea to flex the family again and make sure that your framework and constraints are working as intended. This way, you won’t find yourself half a dozen steps down the line, and suddenly realize that something isn’t working right, but you aren’t sure what.
Other Important Factors
In addition to these basic building blocks of a family, you also have to make sure you define materials. Every piece of geometry in a family requires a material. If the type of material will always remain static, you can establish this by setting a specific material for a specific geometry. If the material is meant to be flexible, however, you will need to set parameters when creating the family, then select the material once the family has been inserted into your model.
Parameters can be set manually, or you can create formulas that establish parameters based on other factors. Formulas allow greater flexibility and efficiency when flexing families and working with variables, as you won’t have to go in and manually create a new set of parameters based on each different size.
Finally, you also have the option to set visibility for a family. If you don’t want the geometry of the family to show in a specific view (such as the plan view) but do want it to show in the 3D view, this can be established when you are authoring your family.
Conclusion
As you have no doubt come to realize, Autodesk Revit is an incredibly powerful tool — but with that tool comes a complex process that must be mastered before it can be used efficiently. While it is possible to learn how to complete tasks such as authoring families on your own, the best way to learn the platform is through Revit courses that give you one-on-on instruction from accredited Revit instructors. Whether you are a beginner or expert, in a classroom setting or a private class, a Revit course is the fast track to proficiency in Autodesk’s industry-leading BIM software.
