Custom Properties and calculated Properties via Expressions in MEP Designer

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Introduction to Properties in MEP Designer

In MEP Designer, Properties are optional,user-defined data assigned too your ducts, pipes, fittings, cable trays, and equipment to provide additional, searchable information. 

Use the Property Manager (Options > Property Manager) to create and delete properties and customize their availability.

Properties work together with classifications and systems: classification defines what the element is, the MEP System defines which system it belongs to, and properties describe its technical and project-specific characteristics.

What you can do with Properties

• List and manage them in the Interactive Schedule
• Display them in Labels,
• Display elements by property, using Graphic Overrides
• Export data structure to spreadsheet, then import property data from spreadsheets into elements.

 

 

 

Types of Properties you will use

In a typical MEP project, you will work with three main kinds of properties:

• Built-in properties
  Core information coming from the element itself (e.g., Size, Length, Elevation, System).

• Custom project properties
  User-defined fields tailored to your standards, such as Fire rating, Insulation type, Acoustic performance, or Installation zone.

• Calculated properties via Expressions
  Properties whose values are not entered manually but are calculated from other data (for example pipe volume).

This combination lets you keep raw model data clean while still deriving all the values you need for coordination and documentation.

How to create Properties - click to expand

 

 

Open Property Manager

• Navigate to Options > Property Manager to access the central hub for creating and managing custom project data.
• You can also open this dialog directly from the Classification Manager. 

Create the Property

• Click the New button at the bottom of the dialog box.
• In the pop-up window, select the radio button for a new Property, give it a unique name, and assign it to an existing group.
• Click OK to generate the property.

Choose a Data Type

• Select your new property from the list on the left and set its Data Type in the right-hand panel.
• This dictates the format of the information you want to capture, such as a String (for text), Number, True/False, or an Option Set (for a drop-down list of choices).

Define Values

• You can optionally enter a description to guide users on how to fill out the property.
• Next, define the property's standard output by setting a static Default Value.

Set Classification Availability

• Finally, configure the property's Availability for Classifications.
• A custom property will only appear in the settings of an element or Building Material if its classification aligns with the availability rules you define here.

 

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What are Expressions?

Expressions are formulas that calculate property values automatically based on other properties or element parameters.

They can use:

• arithmetic operations,
• logical conditions (IF),
• text functions,
• unit conversions.

You typically use Expressions to:

• Avoid manual calculations for repetitive tasks (for example, pipe volume or duct surface area).

• Enforce project rules (for example, choose an insulation thickness depending on pipe diameter).

• Generate “smart” text outputs for labels or schedules (for example, formatted system descriptions).

Expressions are stored as part of property definitions, so once you set them up in your template, every new MEP element can benefit from them automatically.

Create a New Expression-Defined Property: Step By Step

Functions in Expressions
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Practical examples

Pipe Volume (for take-offs)

Calculates the internal water capacity of a pipe.

• Data Type: Volume

• Formula: PI * ( (Diameter (MEP) / 2 ) ^ 2 ) * MEP/Length (MEP) 

Velocity warning

Ventilation velocity is already part of MEP calculation data, and an expression can turn it into a schedule-friendly QA result. Check every rigid duct segment, if the ventilation velocity is bigger than 6 m/s.

• Data Type: String

• Formula: IF (Ventilation Velocity > 6; "Check Size"; "OK" )

 

 

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Why Properties and Expressions matter in MEP Designer

Using properties and Expressions effectively allows you to:

• Reduce manual data entry and recalculation.

• Keep model information consistent across drawings, schedules, and exports.

• Encode your office’s MEP design rules directly into the model.

• Generate more reliable quantities and system-level metrics with less effort.