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Building information modeling (BIM), a process using data to generate digital representations of a facility’s physical and functional characteristics, is the next evolution of design and coordination. Using BIM software is steadily progressing from a project requirement to a preferred design method, including for plumbing design.
BIM’s data and coordination capabilities are our added value beyond construction documents as the software allows every design discipline to analyze data contextually. At Henderson Engineers and Henderson Building Solutions, we use a combination of views within BIM with specific intent.
Collaboration software is only a tool. Design does not happen in a vacuum, so we need to collaborate with others to assess the quality of our work.
When designing with BIM, everything must be in its place from a software perspective and a workflow perspective. It does not need to be exactly right, but there are several downstream advantages to starting in the correct location for elements. Once you satisfy this need, you can move on to viewing those elements.
Design View Vs. Plot View
Design views are used to model and design in context of the rest of the systems. We call this process clash avoidance instead of clash detection. The goal is to use our experience and judgment to lay out the design correctly instead of modeling in a silo, using automated conflict-checking software to perform clash detection.
Plot views have a filtered view of these same elements. They are intended for sought-after construction documents. These views house the annotations to communicate the rest of the design intent. Our plot views follow the WYSIWYG (What You See is What You Get) principle — i.e., designers view the design as it is intended to be viewed by someone else. This helps freshen our perspective and the perception of our systems.
We plot in color, enhancing our drawings’ clarity (Figures 1 and 2). Filters, category-level graphic overrides and object styles are used to show our systems in distinct colors. Care is taken to print the same sheet in black and white and have the same clarity of our design intent as the color plot.
We also chose colors distinct enough from other systems in the same discipline so they cannot be misconstrued. We even go as far as checking for color-blind compatibility. BIM stores all this data, which can easily be manipulated for specific project requirements.
Our quality control (QC) views are used to view specific data of the systems, such as pipe velocity or pressure drop. Modification and corrections can be made live in the model without transferring the data to another software to verify the calculation.
QC views are one part of the automated review process. We also use QC schedules to highlight values outside rule-of-thumb preferred and code-required ranges. These schedules are helpful for fixture counts and mass modification of data from a schedule view rather than a plan view.
Fixture units are preloaded from our custom family library. Like views, our approach to families includes a variety of techniques. We preload all the different fixture units for the various codes into a type catalog of the family. The base family only has generic information stored in the library.
The type catalog loads all the types associated with the code version on a specific project, and the defined fixture units are populated in the model (Figure 3). Connected pipe transfers and sum this information for easy sizing and verification. Our families are generic in nature, but that does not mean they are boring.
We use an approach to separate the connector element, geometry and annotation into subcomponent families. The connector element is associated with its own geometry instead of hosting to the element geometry. This allows us to swap out the generic geometry with manufacturer-specific geometry without affecting the connector properties or globally unique identifiers.
When the family is reloaded into the project, the graphics of the geometry update and the system’s connections remain intact. Simply replacing the generic family with the manufacturer family would break all connections.
The independent connector geometry is useful for moving and orienting the connector without the overuse of parameters, reference planes and split faces. Having all this data inside the Revit database is great. However, we also have a need to extract particular data and check it against our standard design practices. This approach is reserved for data primarily used by a reviewer instead of a designer.
Designing Against Standards
We use Dynamo to extract data and place it in a pre-configured Excel “Design Health” check set file. This is an easy-to-use, pass/fail-type check that can be reviewed outside of the Revit application (Figure 4). We use it to automate the check that determines if the pipe type definitions match our corporate standards, all floor-mounted fixtures are mounted to a floor or at 0 feet 0 inches with the associated level, or all the pipe fittings are industry-standard angles.
Revit almost too easily allows designers to change something they should not be changing and for it to go unnoticed. While we talk a lot about enforcing standards, they are more so guidelines than standards. A standard only goes as far as it is useful.
The standard approach should be the easiest approach for the average designer. That is a challenging thing to narrow down. Simply doing something “because it’s the way we’ve always done it” isn’t a good reason. Henderson is not afraid to allow exceptions to the rules, including traditional industrywide principles.
We routinely create nontraditional sections and 3D views of specific areas worth extra attention. Documenting tight spots is not part of our scope of work but designing a constructible solution is.
Anything that clarifies design intent is worthwhile. Most layout and sheet standards are based on AutoCAD standards, which are based on hand drafting, thus prizing the most efficient way to document design by hand.
Do not judge Revit’s efficacy or efficiency based on hand-drafting standards. Using the right tool for the right job is the mindset, combining data with assets and connecting calculations to the documentation is the job, and Revit is the right tool (currently). So, think outside the box to communicate design intent (and associated data).
Having everything in the design intent location enables clash detection. While our preference is to avoid clashes through conscious decisions, we do not pretend as if automated clash detection is not a great tool to have in the bag. Our approach puts the designer in the driver's seat instead of the software, reducing the clashes to sort through after reviewing model coordination.
We use the Revit Interference Check tool to perform a low-level internal clash detection to review our design. It is not full-on clash detection through Navisworks, which is much more granular and robust. That is a separate process and should involve the entire project design team to make collective decisions on the real issues.
Navisworks allows you to get specific and rule out clashes such as shared code required clearances. Interference Check basically asks, “Does this element hit another element?” It is helpful for the designer to make sure they are not causing any issues with their design.
Coordination Between Disciplines
To coordinate between the different disciplines, we use an unofficial hierarchy of elements that is first aligned by disciplines and then by the element priorities. Our discipline order is architecture, structure, plumbing, mechanical, electrical, fire and technology.
The element priority falls into four categories:
1. Objects generally considered immovable (e.g., large equipment, gravity-fed systems, duct mains, duct banks);
2. Objects that can be moved but require a high level of coordination (e.g., fire sprinklers, large pipe, lighting, MEP equipment, plumbing fixtures);
3. Objects that can be moved but require a low level of coordination (e.g., small diameter pipe, conduit, cable tray, security devices, duct/pipe accessories);
4. Objects that can generally be moved without any coordination.
For example, you would not shift a duct main if it conflicts with a half-inch cold water line. If we have 10 conflicts and seven of them can be handled by the discipline rules, two more can be handled by quick coordination with the element priority, and we can likely schedule a meeting with the design team on the last one if there is a serious issue. The automated check has only highlighted the issue, but we need the designer to solve it.
This process is much more efficient than having everyone go through an autogenerate clash report and deciding who is going to move what. Once the conflict is identified, we make sure to solve the problem.
Simply nudging the element 1/32 inch to the left so it clears the other object does not cut it. Think of the constructability of the solution. A constructible design item is better than a clash-free model. Move the element a couple of inches to allow for installation clearances while checking for code and maintenance clearances.
The Interference Check tool in Revit gets the big item coordination and the smaller coordination items that, quite frankly, make us look dumb. We couple the tool with process and documentation. Running all categories against all categories is not a productive use of time.
We have isolated the common checks to categories by discipline that match the discipline priority matrix and run them in order. Plumbing gets checked against structure (structural columns, structural foundations, structural framing), architecture (walls, doors), mechanical (duct accessories, duct fittings, duct insulations, ducts) and other plumbing (pipe accessories, pipe fittings, pipe insulation, pipe). Of course, that last set could also be mechanical, fire or refrigeration piping.
View templates are used to isolate the specific systems we intend to check. We add automated placement of clearance objects through Dynamo to our underground pipe and are able to automatically locate construction issues that would have traditionally been a manual check. Figure 5 shows the trench clearance requirement in conflict with a structural footing.
Design quality and model quality are not competing objectives. To achieve quality design with BIM, you also must have a quality model. However, if you are looking to cover up a bad design with a good model, you have missed the point.
The approach to reviewing BIM for quality will require a different mindset, toolset and skillset. Most importantly, the process is less about standards-based checking and more about the engineering itself. Even though our project deliverables are 2D construction documents derived from 3D models, we are able to enhance project coordination and overall quality working with BIM instead of in spite of it.
Adam Roth is the BIM/VDC director and a principal at Henderson Engineers.