BIM for plumbing design
Visibility: Some plumbing designers express difficulty with graphics and visibility, especially in regard to printing, with Revit. Part of the solution lies in your view and workset:
- Elements can be hidden or misplaced outside the floor plans. Adjusting visibility graphics allows you to cut the view depth lower than the floor plan. For example, the standard view will not show a drain in the slab. To make it show up, set the visibility view depth lower. You can extend the view into “beyond” mode, which changes line work—a dashed line means it’s not on that level, but it does exist. This may also result in structural or architectural elements showing up along with the below-slab piping. Be aware that this may cause plotting and clarity issues with the drawings when submitted to the authority having jurisdiction (AHJ) or the owner. An alternate solution would be to modify the hidden object by extending it above the floor in order to achieve the visibility.
- Make sure you are in the correct workset. Use filters to display plumbing equipment and pipes in the plumbing views, add all of your components to the plumbing workset, and complete all design in that space. This will enable you to print only the components you want to see and filter out what you don’t want to see.
- Using the underlay option in the properties dialogue box while in a floor plan allows you to see a phantom view of piping or equipment below the floor level you are working in. This is helpful for coordination and layout of pipe runs and riser locations, as well as avoiding conflicts.
Connections: In Revit, plumbing connections are typically shown on the MEP model, not the architect’s model. When an architect updates the model and moves a restroom or deletes a wall, the MEP model assumes the plumbing host is still there. As a result, Revit won’t allow the modification. You can’t just “grab and rotate” the plumbing when an architectural change happens; you have to redo the connections. To speed this process:
- Create a Group and keep it in general relationships; don’t connect directly to fixtures until the architect tells you that no more changes will be made, to avoid having to disconnect and reconnect all piping. We consider it a best practice to not host plumbing piping on objects, as it can save significant time when the architectural background model changes.
- Remember to pay attention to deliverables. It’s not always cost-effective to show every single plumbing connection in Revit, especially for projects where you anticipate a lot of last-minute changes. Waiting to make final connections until floor plan decisions are reasonably complete adds order and flexibility.
Document coordination versus full documentation: There are times when it is appropriate to use Revit for document coordination rather than full documentation. The most important factor in success with this approach is making that decision at the beginning of the job. The cost to fix plumbing mistakes later is comparably high, because water goes through the entire building and can’t be modified in sections. The project team and owner must be on the same page from day one; they must agree on the approach and stick with it.
- Before beginning the design, ask what level of detail is required and clarify the deliverable. Can modeling stop below 2-in. diameter pipe? Can it be performance based? The plumbing only needs to be defined as far as the subcontractor will need it to install, some of which can be done in AutoCAD.
- In our experience, full Revit documentation has worked best on complicated projects where many changes are expected. When using Revit for document coordination only, be strategic in identifying the areas that typically present clash problems. The MEP can’t be fully responsible for all areas due to the lack of exact materials, lack of control over the installation sequence that occurs in the field, and level of contractor experience
- Either way, the use of Revit allows contractor questions to be answered more quickly, because there is more information about the design. The model allows you to visualize the final product on the screen before it’s constructed in the field. And as the level of detail in Revit increases, the speed follows suit. Theoretically, the use of BIM should result in a much better coordinated set of plans which, in turn, should minimize requests for information (RFI) during construction and help keep the project on time and budget.
- Revit also provides a benefit in coordinating with other disciplines. Sloping pipes take up a lot of room in the ceiling plenum, where everyone’s fighting for space. Revit can make collaboration easier for plumbing designers, as they can see the ductwork, cable trays, etc., that are already there, and help the architect set the final ceiling height throughout the building. Ceiling plenum coordination is a significant benefit in areas like Washington, D.C., where height limits put ceiling space at a premium.
Juncheng (James) Yang is a Senior Associate and Plumbing Section Head at GHT Limited. He has more than 15 years of experience delivering highly creative, technically exceptional plumbing designs for commercial, governmental, and institutional projects.