Custom Revit Families vs Generic Components: What Changes on Real Projects?

Custom Revit Families vs Generic Components: Understanding Their Impact on Real Projects

BIM projects often start with a simple question: should the model use standard Revit components, or should custom Revit families be created for project-specific equipment and systems?

For small or straightforward projects, generic components can sometimes provide enough information to get the model moving. But on complex commercial, industrial, healthcare and infrastructure projects, the difference between generic and custom Revit families can become significant.

A Revit family is more than a 3D object. It can contain dimensions, connectors, parameters, materials, classifications and information that support design, coordination, documentation and construction.

For contractors, consultants, builders and BIM teams across Australia, choosing the right approach can affect model accuracy, coordination quality and the usefulness of the final BIM deliverable.

What Are Generic Revit Components?

Generic components are standard or readily available Revit families that can be used without extensive project-specific modification.

They may represent common items such as:

• Air terminals
• Basic duct accessories
• Equipment
• Valves
• Mechanical components
• Diffusers
• Grilles
• Generic plant items
• Architectural or structural objects

Generic families are useful when the exact manufacturer, dimensions or technical characteristics are not yet confirmed.

For example, during an early design stage, an HVAC consultant may know that an air-handling unit is required but may not have final equipment selections. A generic family can represent the approximate size and location without spending time developing a highly detailed object.

This makes generic components useful for early-stage design and concept modelling.

What Are Custom Revit Families?

Custom Revit families are purpose-built components created to match a particular piece of equipment, product, system or project requirement.

A custom family can be developed using actual manufacturer information such as:

• Overall dimensions
• Connection locations
• Duct connections
• Pipe connections
• Electrical connection points
• Access clearances
• Maintenance zones
• Mounting requirements
• Equipment data
• Manufacturer information
• Model numbers
• Performance parameters

For MEP projects, custom families can also include properly configured connectors so that the equipment interacts correctly with ducts, pipes and other building services.

This makes the family more useful than simply having a visually accurate 3D representation.

Why Does the Difference Matter on Real Projects?

The difference becomes noticeable when the BIM model is used for more than visual presentation.

On an actual construction project, the model may support:

Design → Coordination → Documentation → Fabrication → Installation → Handover

If the model contains simplified or inaccurate components, information can be lost between these stages.

A generic component may look correct in a 3D view but have incorrect dimensions or connection locations.

A custom family, when developed from reliable project information, can represent the actual equipment more accurately.

That can improve coordination between different disciplines and provide more useful information for construction teams.

1. Equipment Dimensions Can Change

One of the most obvious differences is physical size.

Consider an HVAC plant room containing several pieces of mechanical equipment.

A generic family may represent an AHU as a simple rectangular box. However, the actual unit may have:

• Different width and height
• Offset duct connections
• Side access panels
• Service clearances
• Electrical panels
• Drain connections
• Multiple sections
• Removable components

If the generic object is smaller or shaped differently from the actual equipment, other services may be coordinated around incorrect geometry.

A custom family can reflect the actual equipment dimensions and connection points.

This becomes particularly important when plant rooms are congested.

2. MEP Coordination Becomes More Accurate

MEP coordination depends heavily on geometry.

Ductwork, pipework, cable trays, structural elements and architectural components all need to occupy the available space.

Using a generic family can create a false sense of clearance.

For example, a generic fan may appear to fit comfortably within a ceiling or plant room. Once the actual manufacturer’s dimensions are introduced, the surrounding ductwork or access zone may no longer work.

Custom Revit families allow the coordination model to reflect the equipment that will actually be installed.

This can help BIM teams identify potential conflicts earlier in the project.

3. Connections Matter More Than Appearance

A common mistake is to focus on how an object looks rather than how it connects to other systems.

For MEP modelling, connectors are critical.

A mechanical equipment family may need accurately positioned:

• Supply air connectors
• Return air connectors
• Fresh air connectors
• Exhaust connectors
• Pipe connectors
• Drain connections
• Electrical connection information

If these are positioned incorrectly, connected systems can also be affected.

A custom family can be configured so that connectors correspond to the actual equipment.

This makes the model more useful for HVAC design and MEP coordination.

4. Clash Detection Can Produce Different Results

Clash detection is only as useful as the information being coordinated.

Imagine a piece of equipment with a generic simplified shape. The model shows sufficient clearance around it, so no significant clash is detected.

Later, the actual equipment arrives with a larger casing, additional connections or access requirements.

The physical installation may then create a problem that was not visible in the original model.

Custom families can reduce this gap by representing the relevant physical characteristics of the equipment.

However, the family should contain the right level of detail rather than unnecessary modelling complexity.

More detail does not automatically mean better BIM.

5. Shop Drawings Can Become More Reliable

Revit models are often connected to construction documentation.

When families contain accurate dimensions and parameters, information can flow more consistently into views, schedules and drawings.

For HVAC shop drawings, this can be particularly useful for equipment layouts, duct connections and coordination details.

A generic component may be adequate for design intent, but construction documentation may require more project-specific information.

Custom families can bridge that gap when they are developed with the intended documentation requirements in mind.

6. Schedules and Equipment Data Improve

Revit is not just a modelling platform. It is also an information management tool.

Families can contain parameters such as:

• Equipment tag
• Manufacturer
• Model number
• Equipment type
• Capacity
• Dimensions
• Airflow
• Weight
• Electrical requirements
• System classification
• Asset information

When these parameters are structured consistently, Revit schedules can provide useful project information.

Generic families often contain limited or placeholder information.

Custom families can be configured around the actual requirements of the project and its BIM standards.

7. Maintenance and Access Requirements Can Be Represented

Equipment does not operate in isolation.

It needs space for installation, inspection, servicing and replacement.

For example, an AHU may require access panels or removable sections. A fan may need service access. Filters may need to be removed periodically.

A basic generic family might only show the equipment itself.

A project-specific family can help represent relevant access zones or reference geometry so that the surrounding design can be checked.

This is particularly important in hospitals, commercial buildings, industrial facilities and other projects where mechanical plant can be difficult to access after construction.

8. Manufacturer-Specific Equipment Can Be Modelled Correctly

Many construction projects eventually move from design assumptions to selected products.

Once equipment has been selected, the BIM model may need to reflect the actual product.

For example, two rooftop units may perform a similar function but have different:

• Dimensions
• Connection positions
• Access requirements
• Mounting arrangements
• Service clearances
• Electrical requirements

A generic family treats them as broadly similar.

A custom family can represent the selected product more accurately.

This can make the model more useful during coordination and installation.

When Are Generic Components Still Useful?

Custom families are not always necessary.

Generic components can be appropriate when:

• Equipment selection has not been finalised
• The project is still at concept stage
• Exact manufacturer information is unavailable
• Only approximate geometry is required
• The model is being used for early design studies
• The BIM requirement does not require detailed asset information

Using custom families for every object from the beginning can also consume unnecessary modelling time.

The key is to match the family development effort to the project’s actual requirements.

When Should You Consider Custom Revit Families?

Custom families become particularly useful when:

The equipment is project-specific

If a component does not exist in the required form within the standard Revit library, a custom family may be necessary.

The project has tight spatial constraints

Plant rooms, ceiling voids and service corridors often have limited space. Accurate equipment geometry becomes more important.

Manufacturer information is available

Once technical data sheets and equipment selections are confirmed, modelling the actual product can improve coordination.

Construction documentation depends on the model

If the Revit model is being used to generate detailed documentation, family accuracy becomes increasingly important.

BIM deliverables include asset information

Projects requiring structured equipment data may need families with specific parameters and classification requirements.

Custom Does Not Mean Over-Modelled

One important consideration is the level of detail.

A common misconception is that a custom family should reproduce every bolt, screw, internal component and manufacturing detail.

That is rarely necessary for construction BIM.

The family should contain the information required for its intended purpose.

For example, an HVAC equipment family may need accurate external geometry, connection points, access requirements and relevant parameters. It may not need every internal component.

The objective should be useful accuracy, not maximum geometric complexity.

A Practical Revit Family Workflow

A structured family creation process can help maintain consistency across projects.

A typical workflow may include:

1. Review project requirements

Understand the BIM execution plan, modelling standards, naming conventions and required level of information.

2. Collect manufacturer information

Obtain technical drawings, data sheets, dimensions and connection details.

3. Build the family

Create the geometry and establish appropriate reference planes, parameters and connectors.

4. Add required information

Include manufacturer, model, equipment data and project-specific parameters where required.

5. Test the family

Check dimensions, visibility settings, connectors, parameters and behaviour within Revit.

6. Coordinate within the project

Place the family into the model and check surrounding ductwork, pipework, structure and architecture.

7. Review documentation

Confirm that plans, sections, elevations, schedules and tags display the required information.

This approach helps turn a Revit family from a simple 3D object into a usable BIM component.

Custom Revit Families for Australian Construction Projects

Australian construction projects often involve multiple consultants, contractors, manufacturers and subcontractors working from coordinated documentation.

That makes consistency and information accuracy important throughout the project lifecycle.

Custom Revit families can support projects involving:

• Commercial buildings
• Industrial facilities
• Warehouses
• Healthcare projects
• Residential developments
• Retail buildings
• Plant rooms
• Refurbishment projects
• MEP coordination
• HVAC installations

The exact family requirements will vary depending on the project’s BIM standards, documentation requirements and construction stage.

Choosing Between Generic and Custom Families

The decision does not have to be either-or.

A practical BIM workflow may use generic components during early design and replace them with project-specific families as equipment selections become available.

For example:

Concept Stage → Generic Components

Design Development → Updated Geometry

Equipment Selection → Manufacturer-Based Families

Coordination → Accurate Connections and Clearances

Construction Documentation → Project-Specific Information

Handover → Required Asset Data

This staged approach can provide a balance between modelling efficiency and project accuracy.

How B&S MechDesign Supports Revit Family Creation

B&S MechDesign provides Revit modelling and BIM support for consultants, contractors and builders working across Australia.

Our Revit services can include custom Revit family creation, mechanical BIM modelling, HVAC modelling, MEP coordination and clash detection.

The focus is on creating practical BIM content that supports design coordination and construction documentation rather than simply producing visually detailed 3D objects.

For projects where standard Revit components do not provide the required level of information or accuracy, custom families can help create a more reliable connection between equipment data, BIM coordination and construction documentation.

Final Thoughts

Generic Revit components have an important role in early-stage BIM modelling, but real construction projects often require more project-specific information.

Custom Revit families can improve the representation of equipment dimensions, connections, parameters and access requirements. When developed appropriately, they can also support MEP coordination, clash detection, documentation and asset information.

The objective is not to make every family highly detailed. It is to make each family accurate enough and informative enough for the stage and purpose of the project.

For complex HVAC and MEP projects, that distinction can make the Revit model much more useful to the people who ultimately rely on it.