Two people learn Revit and take on the same drawing set. The first finishes the model and produces a working schedule. The second takes far longer, and the schedule still comes up short.
The difference is rarely mouse speed. It is that the first person had the right library to hand, and knew how to build whatever was missing. That is why the question of what a Revit family actually is matters more than it first appears.
This article explains families by example rather than by definition. Then come the three kinds of family and when each applies. After that: why firms build their own library, how hard families are to create, and five traps in families downloaded from the internet.
Family, type and instance, through one door
In Revit, everything you place in a model belongs to a family. Walls, doors, columns, beams, furniture, light fittings, pipes — all of it. A family is the template defining a group of objects that share a shape and a behaviour, and differ only in a few parameters.
Take a single-leaf door.
The family is the "single-leaf door" template. It defines that a door has a frame, a leaf and a handle. It defines how the door cuts an opening in a wall. It also defines which parameters may vary: width, height, material.
A type is one specific set of those parameters. "Door 900×2200, timber" is a type. "Door 800×2100, aluminium and glass" is another. One family produces many types.
An instance is each real door standing in the model. The door to room 201, to room 202, to room 203. They share a type, but each has its own position, its own swing direction and its own mounting height.
This three-tier structure has three very practical consequences.
Change a parameter on the type and every instance of it follows. Change the leaf material once and forty doors in the model update with it.
Schedules are generated from families and types. Get the family right and the schedule is right. If a door was merely "drawn" with a few lines, it is not a door, and no schedule will ever count it.
Modelling, in the end, is choosing a family, choosing a type and placing instances. With the right family to hand, modelling is quick. Without it you either build one, or make do with something close and pay for it in the drawings and the schedules.
That is why a Revit learning path for beginners puts families in stage three, and why the Institute runs family creation as a course of its own. Families are what separate knowing Revit from being useful in it.
The three kinds of family, and when to use each
Revit has three kinds of family. Choosing the wrong one is behind most heavy, unmaintainable models.
System families are built into Revit for things assembled in place, either in layers or along a line: walls, floors, roofs, ceilings, stairs, pipes, cable trays. You cannot create new ones. You only add types, by duplicating an existing type and changing its parameters, such as its layers, thickness or material.
Loadable families are built in a separate environment called the family editor, saved as an .rfa file and loaded into a project. Doors, windows, columns, beams, sanitary fixtures, light fittings, furniture, symbols and title blocks all work this way. This is what people mean by a "family library". Edit the family file, reload it, and every instance in the model updates.
In-place families are built directly inside the project for one unique object. A special vault, a curved reception counter. They cannot be reused and they weigh the model down, so keep them for things that genuinely appear once.
The rule for choosing is short. Layered or linear, use a system family. Repeated or scheduled, use a loadable family. Only when it is unique and the other two cannot do it, use in-place.
Within loadable families there is one more idea worth knowing: the parametric family. Its geometry is driven by parameters. Change the width and the frame and leaf stretch correctly. Change the number of risers and the stair redivides itself. Parametric families take longer to build, but one of them covers every size. Without parameters, every size is a separate family, and the library swells fast.
Why a firm needs its own family library
Revit ships with a default library, and thousands of free families exist online. So why do serious BIM firms still build their own and treat it as an asset? Four reasons.
Presentation standards. Every firm and every client has its own conventions for symbols, line weights, text and detail levels. Default families follow foreign conventions. Downloaded families follow whatever their author used. A drawing set built from five sources looks like the work of five people.
Schedules. A schedule is only correct when its families share one parameter set, with the same names and the same units. An in-house library defines that shared set up front — material codes, manufacturer, units of measure — which is what makes model-based quantities usable.
Performance. Families from manufacturers' websites often model every thread, logo and small curve. Excellent for selling a product, useless inside a building model, and heavy. Families built in-house are simplified to what the project actually needs.
The next project. A firm's first BIM project is always slow, because families have to be built from scratch. From the second onward, that work is reused — provided the firm keeps and standardises its families after each project, rather than leaving them scattered in personal folders.
Put another way, a family library is where a firm's experience is stored in a form that can be used immediately.
How hard is it to create a family
The honest answer: simple families are easy, properly parametric families are hard. That gap is why the Institute teaches this as a separate course.
The easy end is a 2D family such as a symbol or a title block, or a 3D family made of fixed solids. A few hours of study covers it.
The hard end is a 3D parametric family that behaves at every size, carries connectors if it is services equipment, and shows different detail at different drawing scales. It also needs the standard parameter set for scheduling, needs to stay light, and must not break when someone else changes a value. That level demands an understanding of geometric constraints, a sense of how the object will be used, and discipline in naming. Self-taught modellers often produce families that work on their own machine and break in a shared project.
The Institute's 8-session family creation course runs from the easy end to the hard one across seven parts. The first three are family fundamentals, system families and an overview of component families. The last four are 2D families, parametric 3D families, advanced and nested families, and in-place families for one-off elements. You need to be able to build a basic model first, which means having completed one of the Revit branch courses.
Connectors for services equipment are the exception: that part sits in the Revit MEP course, not in the family course.
Five traps in downloaded families
Downloading free families is not the mistake. Using them unchecked is. Here are the five traps, and how to spot each.
One: the family is far too heavy. Manufacturer models often go down to individual bolts. A handful of them slows a project noticeably. How to spot it: check the file size before loading, and treat anything unusually large for its kind as suspect.
Two: the wrong category. A door built under "generic model", a sanitary fixture under "furniture". It then misses its schedule, fails to cut the wall opening, and displays wrongly on drawings. How to spot it: open the family properties and check the category before use.
Three: non-standard parameters. Each family carries its own parameter names, so schedules lose columns or report the wrong units. Repairing them one by one usually costs more than building your own.
Four: no detail levels. The family shows full detail at every scale, including a 1:100 plan. Drawings get cluttered and files get heavy.
Five: foreign units and conventions. Families built in inches, with American symbols. Dropped into a Vietnamese drawing set they present incorrectly, and sometimes size incorrectly too.
The safe practice: every family from outside passes one reviewer who checks four things — category, parameters, file size and detail levels. Only then is it renamed to the firm's convention and added to the shared library. With that step, the library is an asset. Without it, it becomes a dumping ground.
Frequently asked questions
What is a Revit family in one sentence?
It is the template defining a group of objects in Revit — their shape, their behaviour and the parameters allowed to vary. From that template come types, and each type is placed in the model as instances.
How do loadable and system families differ?
System families are built into Revit for layered and linear elements such as walls, floors and pipes; you can only add new types. Loadable families are .rfa files built in the family editor for discrete objects such as doors, equipment and columns; they load into a project and travel between projects.
Where is it safe to download families?
The library shipped with Revit, libraries from major manufacturers, and your own firm's library. For anything from outside, check category, parameters and file size before it goes into a project.
How long does learning family creation take?
A few sessions for 2D families and simple 3D ones. Properly parametric families, nested families and services families with connectors need an eight-session course, plus time spent building a library for your own project.
Do structural and services engineers need this too?
Yes, arguably more than architects. Unusual structural elements and services equipment are rarely available exactly as needed, and rebar and equipment schedules depend entirely on families being built to standard.