Give every penetration through a CLT floor or roof a final size and location on the MEP drawings, get the structural engineer to review it, and pair it with a firestop system and an acoustic seal before the panel shop drawings are approved. Keep field cuts for the exceptions, within a limit the supplier and engineer have set.
Why CLT penetrations are different
WoodWorks notes that no U.S. design guide or standard prescribes acceptable openings in CLT floors and roofs, so the engineer evaluates each opening for its loads and panel stresses. The same guidance recommends modeling as many penetrations as possible so the manufacturer cuts them, which is more accurate than cutting on site.
Contractors say the same. The WoodWorks BC and Seagate Mass Timber checklist warns that penetrations not fully coordinated before tender can delay fabrication, and that site penetrations should be avoided. A PCL Construction presentation hosted by WoodWorks lists “maximize shop penetrations made with CNC machine in factory” and “minimize field penetrations” as MEP best practices. Sources verified October 22, 2026. For large projects, see how to track mass timber penetrations through review.
What to record for every penetration
| Field | What to record | Why it matters |
|---|---|---|
| Location | Grid reference, offset dimensions, level, and panel ID. | The fabricator cuts from dimensions, not from a symbol on a plan. |
| Service and size | The service, its size, and the opening size including sleeve or clearance. | A pipe size is not the hole size. |
| Discipline source | The MEP sheet and revision that show it. | Late MEP changes are the usual cause of missing openings. |
| Structural review | Whether the engineer has reviewed it, and any reinforcement or added framing. | Openings near edges, beams, and supports may need a structural detail. |
| Fire protection | The firestop system or tested assembly detail and the floor rating it serves. | Penetrations through rated floors need a tested way to restore the rating. |
| Acoustics | The sealing product or detail at the opening. | Openings can create flanking paths that bypass the floor assembly. |
| Status | Shop cut, field cut within the agreed limit, or open question. | The fabrication release should have no open questions. |
Keep this record in the editable document review log or the project’s penetration tracker, and update it with each MEP revision.
Eight penetration checks before the panels are released
- Every service is drawn. Check that the MEP plans and risers show each penetration with an exact size and location, not only a routing line. The BC checklist asks this question directly.
- Both disciplines agree. Compare each penetration on the MEP plans with the structural panel layout. A penetration in one set and not the other is the most common gap.
- Dimensions, not symbols. Confirm each opening is dimensioned to grids or panel edges so the fabricator can cut it without scaling the drawing.
- Structural review. Confirm the engineer has reviewed each opening, especially near panel edges, beams, and supports, and that any reinforcement is detailed.
- Grouped openings. Look for clusters of openings in one panel. Their combined effect on the panel needs the engineer’s review even if each hole is small.
- Firestopping. Check that each penetration through a rated floor has a referenced firestop system or tested assembly detail. WoodWorks cites IBC Section 714 and systems tested to ASTM E814 or UL 1479.
- Acoustic sealing. Check that the sealing at each opening is specified. WoodWorks notes that flanking paths at MEP openings can be reduced with proper sealing products.
- Field-cut limit. Confirm the specifications or supplier set the largest opening that may be cut on site, and that every trade knows it.
Time the MEP sign-off with the panel shop drawings
A Swinerton Mass Timber scheduling presentation hosted by WoodWorks recommends that the MEPF model sign-off finish together with the mass timber shop drawing review, and that coordination happen months earlier than on a conventional project. The PCL presentation describes modeling all conduit on one project and overlaying the penetrations on the CLT shop drawings.
In practice, this means the MEP engineers must commit to sizes and locations before they normally would. Agree on a date for the MEP freeze, and treat any change after it as a change to the fabrication package. See the mass timber drawing coordination checklist for the other items that must be settled at the same time.
Published example: an opening shown in only one discipline
This finding comes from a concrete project, not a mass timber one. In the published missing-opening finding, a sump on the mechanical and plumbing plans had no matching opening in the structural slab and footing information. In a CLT floor, the same gap would reach the factory unless both sets are compared before the panels are released.
Where Groundbook fits
Upload the architectural, structural, and MEP drawings with the relevant specification sections, and run a cross-discipline review. Groundbook flags potential disagreements, such as an opening shown on an MEP plan but missing from the structural panel layout, with links to each source sheet. Your team decides what each finding means for the fabrication package. Groundbook does not check structural capacity, fire ratings, or the fabricator’s model.