Revit 2024: Improvements to MEP Fabrication Data Quality with Straight Adjusts 

Martin Schmid April 13, 2023

5 min read

Relevant MEP Fabrication products: CADmep, ESTmep, CAMduct, Revit 


To have more consistency and predictable behavior in the generation of flat pattern developments, our team has prioritized several efforts to address a variety of user-reported issues. Historically, these issues would have been addressed in isolation, one by one, resulting in varying levels of inconsistency in the behaviors and flat pattern development results of various duct fittings. Taking a more holistic approach now, these efforts are more extensive in nature than one-by-one fixes. By doing a comprehensive evaluation of the logic, we hope to resolve a variety of issues, and at the same time, put into place much needed test automation to maintain the long-term health of the code and avoid unexpected changes in future behaviors, as we continue to address other types of issues that are dependent on this first effort. This effort for “Straight Adjusts” is the first step in starting to tackle the other improvements related to “MEP Fabrication Data Quality” that have varying levels of dependencies on how parts are expanded into flat geometry. Said another way, other improvements depended on addressing this area first. 

Improved in Revit 2024

The focus for the 2024 release was to resolve flat pattern development issues which were a result of inconsistencies in how the “Straight” property on connectors interacts with the “Extension” related properties at the end of rectangular fittings.  

How Does the Straight Property on Connectors Affect Developments? 

Generally, the Straight property on connectors applies a defined minimum straight length at the ends of fittings. For example, the image on the left shows an elbow (such as pattern 4) with 0 Top Extension and 0 Bottom Extension. The image on the right shows the effect of this behavior after applying a connector with a Straight value of 1.0.  We’ve taken a comprehensive pass through all patterns to have better consistency and addressed several issues along the way.   

Left image shows a fitting with no connector and 0 Extension length values. Right image shows the effect of applying a connector with a Straight value larger than the Extension defined on the fitting. 

Example Demonstrating Previously Unaffected End 

An example of the prior inconsistency where the Straight setting from the connector would not affect the part is shown below. In this case, the applied connector has a Straight value of 2.0, and the part has a user specified dimension of 1.0.  In the image on the left, the connector’s Straight 2.0 distance is not applied to the “f” dimension in prior releases. In the 2024 Release, the behavior has been improved to be more consistent. 

Prior releases 
2024 Release.

Example Demonstrating Dependent Flat Pattern Development Details 

These inconsistencies in prior releases also had knock-on effects on other aspects of generating flat pattern developments. For example, holes for taps, holes for stiffening reinforcement, notches, splitter holes, and the like, may have been unexpectedly applied. In the example below, the image on the left shows the hole for midpoint stiffening reinforcement in the development previously adjusted unexpectedly due to the connector applied Straight. The image on the right shows the expected position of the stiffener in the 2024 Release.  

Position of hole for stiffening reinforcement in prior releases.
position in 2024 Release.

Part Preview and Area Computation 

Finally, previously, the development preview did not clearly depict the finished fitting outline, and the computed area “Item Duct Area (No Allowances)” value was not consistently reporting the finished silhouette area of the fitting. In the images below, note the position of the arrows pointing to the grey line across the width of the elbow. This made it difficult to interpret where other aspects of the development, such as stiffener holes (shown in red), were relative to the finished fitting outline. The image on the right shows the improved finished fitting outline where the position of the stiffener hole relative to the fitting end is more easily validated. Also note that the corrected area value reflects the silhouette area of the finished fitting. 

Prior releases.
2024 Release.


The above examples are illustrative of the types of behaviors that have been refined to provide better predictability and consistency across all parts that share similar characteristics.  Due to the interdependency of a wide variety of settings, it is not feasible to attempt to enumerate all the applicable conditions and cases that have been improved to make the behavior more consistent.   

The list below enumerates some key patterns that have functionality related to this connector Straight property adjustment behavior.  

Fitting Type Pattern Numbers 
Parallel Bend and Reducer 1126 
Parallel Bend and Square to Round 1127 
Parallel Bends 1124, 1125 
Parallel Tapers 1128 
Rectangular Bend 3, 4, 17, 20, 22, 23, 250, 251, 354, 420, 421, 430, 431, 526, 761, 819, 943 
Rectangular Branch 7, 417, 947 
Rectangular Branch on Rectangular Straight 32, 150 
Rectangular Branch on Round 904 
Rectangular Chimney 343 
Rectangular Double Radius Offset 836 
Rectangular End Cap 12, 401, 958 
Rectangular Grille Box 19, 21, 26, 31, 382, 861, 956, 957 
Rectangular Junction 10, 14, 18, 800 
Rectangular Offset 6, 11, 30, 252, 366, 460, 461, 955, 979 
Rectangular Radius Offset 9, 330, 367, 939, 944 
Rectangular Taper 2, 27, 253, 342, 440, 441, 920, 942, 959, 1148, 1178 
Rectangular Tee 5, 13, 255, 470, 471, 945, 954 
Rectangular to Oval 104, 134, 137 
Rectangular to Round 8, 28, 29, 34, 254, 324, 338, 450, 451 
Rectangular Trousers 328, 480 
Reducing Bend 953 
Square Bend 952 

Dimension Input vs Result 

One final note regarding maintained behavior: When the connector is enforcing minimum length, there are overrides to prevent fitting ends from overlapping or shifting the model in potentially undesirable ways. As a result, the dimensions a user inputs for a part, including the Top/Bottom Extension, and the Inner Radius as exemplified in the image below, may not reflect the result when measuring the model. For example, values shown in the property grid, printed worksheets, and labels may not match the actual resulting geometry when measured in the model on a flat pattern development. For example, a rectangular connector may have a Straight parameter value of 1.0,” however, a user may set the Top and/or Bottom Extension to some value less than this. The image below shows a user input length of 0.0”.  In such a case, the 1.0” from the connector is enforced, resulting in the “D” and “E” dimensions on the model and related geometry in the flat pattern development reflecting that value. Further, the Inner Radius, explicitly set as 12.0”, is overridden to 11.0”, again, to preserve the fitting endpoints. This is an area of legacy behavior that we’d like to improve at some point to provide more clarity regarding these ‘entered’ vs. ‘overridden’ values, but it presently isn’t something that is a priority for a planned project. 


This work provided the opportunity to improve the foundation for future improvements. Additional areas under consideration related to “MEP Fabrication Data Quality” may be found on the Revit – MEP public roadmap

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