How Drawing Review Caught a Duct Clash on a Boston Campus Building
- A 6-inch duct crossed a joist at a grid where the largest allowed hole is 2 inches, so the duct could not be built as drawn.
- Helonic, AI drawing review software, read the mechanical and structural PDFs together and found the clash, even though a BIM team was on the project.
- A 6-inch duct against a 2-inch hole limit is a 3x gap that the BIM team's model coordination had not caught. The owner's rep resolved it in the drawings.
Boston, MA. 6-inch duct vs. 2-inch hole limit.
Lead Finding
6-inch duct crossing a joist
The Limit
2-inch largest allowed hole
Project Setup
BIM team on project, clash missed
A 6-Inch Duct Through a Joist That Allows a 2-Inch Hole
An owner's rep was reviewing the drawings for a higher education campus building in Boston. A BIM team was on the project and was running model coordination, so the major clashes were expected to be handled there.
The mechanical drawings routed a 6-inch duct across a joist. At that grid, the structural drawings limited the largest hole allowed through the joist to 2 inches.
A 6-inch duct will not pass through a 2-inch hole, and the joist could not be cut to make room. The duct could not be installed as drawn.
Helonic Read the 2-Inch Hole Limit Against the 6-Inch Duct
The owner's rep uploaded the PDF set. Helonic read the mechanical layout and the structural framing together, including the joist notes and the hole limits.
The finding that mattered most was a 6-inch duct overlapping a joist at a grid whose largest allowed hole is 2 inches. Overlaid, the duct's path crossed the joist at that grid, and the opening allowed there was a third of the duct's diameter.
The clash had not been caught in the model coordination. A geometry check flags objects that touch each other. A hole-size limit is a rule written on the structural sheet, so a check that only compares shapes has nothing to measure it against. Helonic read the rule and compared it with the duct size on the mechanical sheets.
On site, the options at that grid are to re-route the duct, move or reinforce the joist, or re-engineer the framing. Each one needs the engineer of record, revised shop drawings, and rework to anything already hung. On paper, it is a change to one duct route.
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A Clash a BIM Team Had Not Caught, Found in the Drawings
The owner's rep sent the clash to the design team with the duct size, the hole limit, and the grid marked on the sheets. It was resolved in the drawings, by re-routing the duct or adjusting the framing at that grid, before anyone tried to build it.
A BIM team was on the job, and the clash still reached the issued drawings. A check on the PDF set found it.
Helonic reads the issued drawings the way the trades will, so it checks what is on the sheets as well as what is in the model.
A BIM process does not remove every cross-discipline miss. Across 1,000+ drawing packages Helonic has reviewed, about 8 in 10 had at least one coordination conflict between disciplines. See what Helonic found across 1,000+ drawing reviews.
Massachusetts 780 CMR and Why a 2-Inch Hole Limit Lives in the Structural Notes
Boston permits buildings under the Massachusetts State Building Code, 780 CMR, which adopts the International Building Code with state amendments.
The building code does not list hole sizes for joists. Those limits come from the joist manufacturer or the engineer of record, and they are printed in the structural general notes or on the framing plan. The code requires the structure to be built as designed, so the notes carry the weight of the design.
That is why model coordination missed it. A clash check compares geometry. A hole limit is text on a sheet, so there is nothing for the geometry to touch until someone reads the rule against the duct size.
“The project had a BIM team and this still got through. A 6-inch duct on a joist that allows a 2-inch hole. You can't build that. Helonic found it from the drawings.”
Boston Campus Building Drawing Review: Questions and Answers
What was the main finding on the Boston campus building?
A 6-inch duct overlapped a joist at a grid whose largest allowed hole is 2 inches, so the duct could not fit as drawn.
Why was it not caught in the BIM process?
A geometry check flags objects that touch each other. A limit on hole size is a rule written on the structural sheet, which a shape-to-shape check does not compare against. Helonic read the rule and compared it with the duct size.
Can a 6-inch duct go through a 2-inch hole?
No. The duct has to be re-routed, or the joist has to be moved, reinforced, or re-engineered, and each of those is a design change.
Does Helonic replace BIM coordination?
No. It adds a check on the issued PDF set. On this project it found a clash that the model coordination had not.
Which building code applies in Boston?
The Massachusetts State Building Code, 780 CMR, which adopts the International Building Code with state amendments.
Where do joist hole limits come from?
The joist manufacturer or the engineer of record. They are printed in the structural notes or on the framing plan, not in the building code.
Can clash detection software read hole limits?
Geometry-based clash detection compares shapes in the model. A hole limit written as a note has no geometry, so it takes a check that reads the sheet text against the duct size.
Milind Sagaram
Co-founder & CEO, HelonicMilind is the co-founder and CEO of Helonic, where he leads product and go-to-market for AI-powered construction drawing analysis. He works closely with general contractors, project managers, estimators, and owners to understand how drawing quality drives project outcomes - and where AI can reduce RFIs, change orders, and rework. Milind has interviewed hundreds of construction professionals across project delivery roles, from preconstruction estimators at ENR top-400 contractors to facilities directors at institutional owners, and uses those conversations to shape both product direction and the way Helonic talks about the work.
- Construction project delivery and preconstruction
- RFI and change order economics
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How this page was researched: Reviewed against Helonic's 2026 drawing-analysis categories, RFI workflow, and product capabilities.
Last reviewed by Milind Sagaram · October 4, 2026