The ABCs of MEP Construction Modeling, Part 2
In Part 2 of this two-part series on MEP trade construction modeling we continue discussing shop drawings and submittals and focusing on how to best use Autodesk® Revit® MEP for trade construction modeling. For Part 1 of this article, please refer to the October 2014 issue of AUGIWORLD.
Why Use Revit for MEP Trade Modeling?
Many MEP trade contractors are still using AutoCAD® or AutoCAD-based fabrication tools such as Autodesk’s own CADmep+, so the question of why we would want to use Revit MEP for trade contractor modeling and shop drawing production is an important one.
First, it is important to understand where the industry is and in what direction it will be moving. It was clear from Autodesk’s acquisition of MAP Software in 2010 that they intended to fill the gaps in their building construction portfolio for MEP fabrication, a critical factor in the success of any building construction effort. Combined with Navisworks® and Quantity Takeoff, we now have all of the tools to leverage BIM for construction.
Sadly, the MAP Software acquisition was not without quite a bit of pain. The CADmep application is an AutoCAD-based add-on, and thus was a straightforward port to an Autodesk rebranding. However, their Revit-based product, FABmep+, came with a lot of legal strings attached, which caused Autodesk to discontinue the product in the 2014 release cycle (March of 2013).
However, Autodesk is clearly intent on making Revit a design to construction, end-to-end solution platform for BIM. They are actively working on the successor to FABmep+, which will bring fabrication-level Revit content and workflows to the MEP trades. This will dovetail with Autodesk’s ESTmep application for estimation and Fabrication CAMduct for automated duct fabrication.
Given the rapid rate of BIM adoption by the design and construction industry, it is important for MEP trade contractors to consider adopting Revit and a BIM workflow as soon as possible, to eventually be able to take full advantage of this technology and not be left behind.
Secondly, even without the additional trade-specific Revit content provided by FABmep+, you would still see massive gains in productivity as you leverage the Revit platform using the provided toolsets for laying out and documenting duct, piping, conduit, and cable tray.
Background Models and Shop Drawings
As we discussed in Part 1 of this article series, design models are usually not up to par for the purposes of MEP trade coordination, so the initial part of the MEP trade construction modeling process is to somehow acquire accurate architectural and structural construction models for use as backgrounds. Today this often comes under the purview of the construction manager (CM) in order to leverage BIM across all trades, so the CM will typically provide the background models to the rest of the construction team and perform coordination. This typically goes one of three ways for the MEP trade modeler.
Construction managers may subcontract out the creation of base architectural and structural models to hand over to the MEP trade contractors. This is often the case with non-BIM projects. However, the CM may not be experienced enough to properly specify the necessary requirements and protocols, so you may end up with inaccuracies or other issues. I’ve seen cases where they farm out the modeling to a company that, in turn, subcontracts the work to an offshore company, which then models all of the architectural and structural components in Metric instead of Imperial units or vice versa. In the delivered model, every length, component family member, and system family layer is an oddball dimension and this has radically compounded errors across the project.
If you are very lucky (or very unlucky, depending on your point of view), you may get the contract to model everything yourself. While not ideal from a sanity standpoint, it does afford you ultimate control over the modeling process and can provide a very clean coordination phase.
The ideal scenario is to receive models that directly incorporate or are a result of the fabricators’ shop drawing process for structural and architectural components. Based on the construction documents, the concrete and steel detailers create the fabrication-level shop drawings. Once they have been reviewed and signed off by the structural engineer, the structural shop drawings have the final say in what is fabricated and installed, so any model based on these would be authoritative for your use. They contain precise framing spacing, slopes, and top of steel elevations, as well as all of the pertinent structural details used for fabrication.
Figure 1: Typical structural steel shop drawing of a roof truss
Many of today’s structural detailers use specialized, model-based software for their shop drawing production, so you may or may not get lucky and be able to obtain something that can be used directly in Revit. Revit 2015 now features IFC Linking, which should be a boon for construction modelers who need to repurpose foreign file formats. While the accuracy of IFC components has historically been a problem, the format is gaining steam and is actively being developed independently of Autodesk, which should help ameliorate these kinds of issues.
Figure 2: An IFC structural model
Architectural shop drawings also play a critical role in the overall modeling process. Detailed, approved shop drawings for exterior precast panels, curtain wall/storefront assemblies, and casework are all often necessary for properly coordinating with MEP.
Submittals
A large part of the trade modeling process is to collect and review the approved submittals for all mechanical HVAC, piping, plumbing, and electrical components. This can be a long, drawn-out affair as contractors evaluate the cost, lead times, installation requirements, and cost (again) of each and every component they intend to supply for the project.
The submittal approval process may take longer than planned, and you will definitely not have everything in place on day one. The specifications dictate what manufacturers are approved, and the drawings may even provide model numbers as a basis of design, but contractors will often request substitutions, which may take time to get answers. Just like structural shop drawings, the approved submittal ultimately dictates what is going to be installed and, thus, what is to be modeled.
Approved equipment submittals can have a huge impact on the coordination process. For example, I’ve seen the case where a design team uses a specific air handler and properly bases their HVAC designs on the unit’s parameters for port sizes and locations, overall size, and so on. However, the unit’s submittal that comes back from Johnson Controls is very different from the drawings. In reality the unit is about five feet longer, two feet wider, at least a foot taller, and has two new sections added for access. The supply and return air connections are larger, requiring modifications to the supply and return air ductwork. Additional ports for a glycol recovery loop between two coil units are included, but not shown in any drawings. Because of the increased size, it now requires careful placement in the mechanical room to avoid encroaching on nearby electrical panel clearances.
Coordination Timing
Probably the biggest problem with the BIM coordination modeling process is one of sequencing and timing. Typically, concrete and structural steel shop drawings are the first to be completed because the structure is the first thing to be built. However, the MEP contractor is already on site from day one, working in the field hand in hand with the concrete and steel trades, laying underground duct banks, piping, and placing sleeves. Things move very fast on site—as soon as the steel is up on one floor, the other trades descend on it to place hangers, ductwork, piping, and conduit. Thus, the MEP trade modeling efforts will need to be properly phased early enough into the coordination process as to not hold anyone up in the field. Be forewarned: MEP modeling is extremely labor intensive and even with simple buildings it can take a long time to model all the systems.
Initializing Your MEP Construction Models
Regardless of how you acquire the base background models, my typical MEP modeling workflow goes something like this:
I usually start by creating an authoritative datum model that establishes the overall shared and project coordinate systems, levels, grids, and any important reference planes. It’s really a utility model; it has no real geometry, is very lightweight, and can be linked into other models and used to easily acquire/publish coordinates, copy over datum, and other useful tasks. Set the locations of the project base point, shared coordinate point, and true north from a linked civil model or CAD drawing. Set up all of the levels and grids, and be aware of the grids’ 3D extents, ensuring the correct grids apply for each level. Place and name all of the important reference planes, such as the building’s axes or centerlines. Incorporate scope boxes and propagate extents to set up views and datum graphics.
I also ensure all models have their units set to the highest level of precision available—1/256”. This allows me to easily identify poorly located elements and quickly fix errors, which usually fix adjacent errors in the process. I like to keep my models honed. If I see weird x/256” dimensions, something is probably not located right. If it’s an odd building with lots of odd dimensions, I’ll use alternate units to display rounded values.
If I’m also modeling the architectural and structural backgrounds, I treat the set of linked models as a giant 3D jigsaw puzzle. I determine who owns what and model each element once and only once across the project. A concrete floor slab is typically structural, so it goes in the structural model only. Because of phasing during construction, you may opt to split up wall assemblies across models, putting the non-load-bearing portions that get built later (face brick, air space, insulation, sheathing, interior furring studs, and wallboard) in the architectural model, and the major load-bearing CMU portions in the structural model.
Leverage the use of parts in your structural and architectural models. Breaking up system family elements such as walls, floors, and roofs is required for some construction types and typically provides better accuracy for coordination, enhanced quantity takeoff (QTO), and advanced 4D sequencing.
Take advantage of all the available tools. Use split face and paint for zero-thickness finishes such as paint and wallcovering. For non-zero finishes create thin floors, walls, and ceilings. And don’t worry about modeling outside the box. I will often model railings as curtain walls and use in-place modeling of sweeps for casework and corrugated metal decking where necessary.
A certain amount of discipline-specific organization goes a long way. Each linked model gets its own set of project datum (levels and grids) and should be identifiable as such. Set up different discipline-specific head symbols and color-coded types for structural, architectural, and MEP datum, and apply them in all of your trade contractor models. Use instance-based project parameters and filters to turn them off in documentation views.
Figure 3: Structural, story, and general datum level types
Link the architectural and structural models into each other and into the MEP model, and copy the levels and grids as required. Don’t make Revit work any harder than it needs to—at this stage you won’t need to monitor the datum between the models as they probably won’t change (if they do, you have bigger problems).
You will want to turn off visibility of the linked datum elements easily, which you can do with a specialized view template. In any plan, elevation, or section view, modify the View/Graphics Overrides for a Revit link, setting it to custom and turning off the annotation, analytical, and import categories completely. Then create a special “Link Model Prep” view template from this view that has only the RVT Links section checked. Apply this template to all views, which will instantly switch off the linked model datum. Note: Remember that this template is specific to the RVT links you have loaded at creation time. If you rename a linked file or remove/reload it, the template will no longer function and will have to be rebuilt.
Figure 4: Creating a view template specifically for RVT links
To fully coordinate between the architectural, structural, and MEP models, you will necessarily bounce back and forth between all of them to make required changes generated from the MEP modeling process. These would include creating the required duct penetrations, pipe and conduit sleeves, electrical outlet poke-thrus, and so on.
Modifying the backgrounds to coordinate with MEP elements reduces the false positives during clash detection and allows all of the models to be used for locating these critical features in the field. It’s much less expensive to accurately form out a 12” hole for a steam pipe sleeve in a foundation wall when it is poured rather than have someone core drill it later on demand. Note that penetrations in structural walls may require modifications to the rebar, so these conflicts should be identified as early as possible and passed to the engineer for approval. If your structural model has the rebar modeled, so much the better.
Figure 5: Pipe sleeves set in CMU walls
If others are responsible for the architectural and structural models, be aware that these models may be updated after you start your MEP modeling, so you may need to refrain from making any MEP-driven changes yourself. Instead, coordinate the MEP-driven changes via frequent sketches back to the CM so they can have their modeler incorporate them and provide the updates.
Starting Your MEP Modeling
Now that you have the drawings reviewed and marked up, are familiar with all of the systems involved, and have solid architectural and structural models linked into your new, blank MEP model, it’s time for the real fun to begin. And by “real fun” I of course mean endless tedium, long hours, lost weekends, and unhappy significant others.
Starting with a well-developed MEP template that has a lot of the typical settings and system/component family types is crucial. You need to get off the ground with basic duct, pipe, and conduit types that have most of the required fittings and behave the way they should.
I typically start by creating all of my duct and piping system types as well as my duct and pipe types. This involves the following tasks:
Modify/duplicate the duct and piping system types as required. These are first and foremost identified by the system classification, which is inherited by the system type that was duplicated. System classifications allow Revit to determine how systems and MEP family connectors work together. System types also determine what media it is carrying (air, water, gas, etc.), the conversion and calculation method used for sizing, and the graphics overrides that will automatically be applied in all views.
Review the specifications for the pipe and conduit materials, the systems in which they are to be used, and the sizes used for each material. Incorporate these materials into the mechanical and electrical settings as required for the various duct, pipe, and conduit types. Ensure that the proper true ID and OD sizes are input for each trade size. Remove anything not required in order to eliminate confusion.
When defining the pipe and duct types, take the time to flesh out the routing preferences. Ensure that the segments and sizes are properly enumerated. For example, the specifications may call for copper Type M for pipes NPS 2 or smaller, and Schedule 40 steel pipe for NPS 2 ½ and larger. Each requires different fittings and segment materials that can be set in the routing preferences.
Figure 6: Adjusting a pipe type's routing preferences
Ensure that for each of these material types you create and/or load the proper component families for fittings and unions, and update the routing preferences accordingly. This is particularly important for larger drain pipe, as these elbow fittings have longer sweeps and take up much more room than the default elbow, which definitely will affect coordination. Note that in Revit 2015 there are new ductile iron and steel pipe fitting families based on AWWA standards.
For duct types, set up the routing preferences with fittings based on the contractor’s shop standards. The contractor may call for TDC duct for anything 8”x8” and over, and use Slip & Drive for smaller duct. Or they may reserve TDC duct only for ducts 20” and larger. They may want transitions to be 18” typical, flat on one side if possible, elbows with 6” throats, with extended throat sizes in order to economize on cutting a piece of duct. Create fitting families for all of these items, including volume dampers as required. Do whatever you can to make the duct layout easier the first time around.
Review the specifications for duct elbow information. Are they angled or radiused? The drawings may indicate radiused elbows, but the duct subcontractor may prefer square 90-degree elbows with turning vanes, which are actually very efficient. If they are to be radiused, check the specifications to see what the radius ratio to duct size is required. Do not rely on the drawings, as they may have been drawn/modeled incorrectly. Having to increase the elbow radius from 1x duct width to 1.5x duct width across a tight plan can introduce all sorts of new clashes with other work.
Get a copy of the SMACNA “HVAC Duct Construction Standards, Metal and Flexible” manual and read it thoroughly. It documents and details many of the things you will need in the construction model.
General MEP Modeling Considerations
While it’s important to understand what to model, it’s just as important to know what not to model. BIM Execution Plans (BEP) will often dictate this, but always confirm with the MEP coordinator about specifics. For example, the BEP may specify that all conduit 1” trade size and over is to be modeled. But there may be plenty of instances where 10 or more ¾” conduits are ganged together and running through a space. Ensure that these are accounted for.
One of the first things many modelers do is go on a Revit family treasure hunt, scouring manufacturer sites for equipment, light fixtures, and other content. Sometimes it is worth the effort, but just as often it is not. Just because a family comes from a manufacturer does not mean it works well. Often I see families that are way too geometrically expensive and complicated in how they were built, inconsistent from one model to another, and just difficult to use in the real world. In my view, the best families have few types and address project-specific conditions. Tip: the ENGworks BIMXchange add-in (http://www.engworks.com/BIMXchange/bimxchange.html) is a very good place to find well-modeled families from a number of popular equipment manufacturers.
No matter what family I am working with, I ensure all families include at a minimum the identity data for manufacturer, model number, assembly code, and other pertinent information that could be useful to the owner downstream. Work with the MEP coordinator to define what things can be added to the Revit content that will help him or her in Navisworks, such as links to submittal PDFs. I generally include type comments, but rarely tag from them, instead relying on more direct information for documentation purposes if required. Check with the BIM Execution Plan for any required parameters.
To ensure the family is as light as possible in plans, turn off 3D geometry for plan views and incorporate 2D symbolic linework instead. It’s often easiest to use a nested 2D detail item family.
Subcategories
Because the “Mechanical Equipment” and “Electrical Equipment” categories are so all-encompassing, make use of subcategories for specific kinds of equipment, such as expansion tanks, air separators, heat exchangers, water heaters, and so on. Create and assign these to the geometry in the families, and they will come into the project environment and allow you to fine-tune their appearance in views.
Figure 7: A partial list of mechanical category subcategories. Note the use of “Clearance” subcategories with assigned materials
MEP Connectors
MEP connectors are really what allow Revit MEP to function. You need to understand system classifications, flow direction, and controlling the flow and size using linked family parameters to make the connections to duct and pipe behave correctly. For air terminals, the connector needs to be set to Preset, which allows the user to define the CFM at the terminal. Additionally, the connector’s flow parameter must be mapped to a flow family parameter. You can actually name the flow family parameter whatever you want, and as long as the connector is set to preset and its flow parameter is mapped to the family parameter, it will schedule under the “Flow” field. Note that this connector must be the primary duct connector in the family.
For mechanical air-handling equipment, the connecters are set to “calculated” to calculate the total airflow to or from the air terminals and/or VAV boxes. Because we typically aren’t actually designing the MEP systems for performance (that’s what engineers are for), your connectors can be a little loose on defining loss methods, pressure drop, and other nerdy engineering considerations. However, I highly recommend you always provide a connector description, particularly on complex pieces of equipment, so that when you create systems you can readily assign them to the proper connectors on a multi-connector equipment family.
Figure 8: Typical VAV box connectors and their descriptions
Specific MEP Modeling Considerations
For electrical panelboards, I start with a prototypical panelboard family I created that has some typical standard sizes built in. I then create dedicated types named for each and every panel in the project, sized appropriately. This makes it easy to place panels and identify each one. It includes Unistrut supports that can be turned on or off based on the mounting condition.
I use the panel schedules to define some specifics in the panel type, but because electrical modeling is mostly about locating panels, equipment, and snaking conduit/cable tray through the building, I usually don’t get hung up too much on the engineering aspects. I typically don’t wire up any devices or worry about modeling flexible conduit, for example.
However, included in all panel families are boxes that accurately show the required clearances for the dedicated electrical space above the panel, and the working space in front of the panel, as outlined in NEC 110.26. You would be surprised at the number of electrical designers who do not take this into account, and it can really affect coordination. Relocating a panel during construction because its clearances clash with nearby elements is always expensive, because it means more cable, conduit, and labor.
Figure 9: A typical panelboard family with code clearance geometry
As a general rule I include clearance geometry (assigned to a subcategory) in almost all other mechanical and electrical equipment as well, using a standard “Clearances” material, which is a transparent pink color. These clearance boxes allow us to clash test for contractual and code compliance.
For suspended equipment, such as VAV boxes and unit heaters, I include simple hanger families with instance parameters for controlling the suspended height as well as the length to the underside of structure. I tend to model VAV boxes with the center of the duct at the reference level to make its offset value the same as that of the duct. For unit heaters I generally model the bottom at the reference level, making vertical placement above the floor (as well as tagging) easy in the project by specifying the offset instance parameter.
With air terminals—more appropriately termed grilles, registers, and diffusers or GRDs—I’ve found that some manufacturers have excellent families available and some manufacturers have none. Since most GRDs are the same or very close to what you need, grab some of that work and modify them as required. Note the neck sizes and shapes as well as the airflow pattern.
For mechanical piping systems, particularly steam systems, there are a lot of components to deal with. You have gate, globe, butterfly, and air-assisted pressure relief valves, strainers, thermometers, gauges, flexible connections to equipment, expansion tanks, air separators, pumps, heat exchangers, condensate traps… the list is endless and it all needs to be modeled to some degree. The submittal cut sheet will usually have good dimensional information to work with.
For duct and pipe I need to add insulation, but also always need to see the underlying geometry, so I create insulation types for each thickness that have a transparent material.
Figure 10: Transparent insulation materials
Plumbing fixtures and fixture supports (carriers) can be modeled as individual families and nested into a single fixture family with the proper connectors placed. For water closets I usually nest the carrier and the flush valves, linking parameters to the host family where required and remembering to make left- and right-handed versions. Mirroring plumbing fixtures is a “no-no”!
I will often model sinks complete with the faucet, p-trap and run horizontal “pipe” segments into the wall for sanitary/vent and hot/cold water supply, and include all of the necessary connectors there. That allows me to easily add the sink to the domestic cold water, domestic hot water, sanitary, and vent systems in one shot, and pipe up things easily.
Hangers and supports take up real space, conflict with real things, and need to be modeled. Providing these early helps the trade contractor mobilize people on the job site and better coordinate between trades in dense locations. These also contribute to prefabrication, which saves everyone time and money. Fully parametric unistrut racks and hangers for conduit and electrical equipment are pretty easy to make, as are saddles and clevis hangers. For strut-like hangers, I base the elevation on the underside of the things being supported. For pipe hangers I usually base it on the elevation of the center of the pipe.
Figure 11: A typical service tunnel with pipes, supports, and hangers
Placing Equipment
After I gather up or model my equipment families, I try to locate as much of the mechanical equipment, lighting, plumbing fixtures, and GRDs at one time throughout the building. Don’t try to pipe or duct anything up just yet—that requires coordination with structure and equipment and best comes later. Give the GRDs the proper CFM values per the HVAC drawings; I always tag them as well as run a schedule to double check.
For GRDs and light fixtures, special consideration has to be taken into account with regard to how you handle the ceiling. Ceilings are usually “owned” by the architect, but the MEP engineer needs to poke all sorts of holes in them, which leads to coordination breakdowns. For placing diffusers and lights in an MEP model, which may need to cut the ceiling plane, you have three options:
- Put the ceiling in the MEP model and place ceiling- or face-hosted families that cut their host. Not always easy, especially when you do not control the architectural model.
- Leave the ceiling in the architectural model. Place face hosted or unhosted families in the MEP model and don’t worry about cutting the ceiling object.
- Do option 2 with unhosted families, then place parallel “void only” families in the architectural model, which cut a hole in the ceiling that matches where the ceiling components are in the MEP model.
Of the three I typically prefer option 2, then if I can, move to option 3 using unhosted families. As the design is finished, we can use unhosted families and not worry too much about moving walls or ceilings. I’ll prefer to have the ceiling in the architectural model as I don’t want to have to deal with it specifically in the MEP, but also want the hole as well. I’ll usually wait until the location of the GRDs and lights is finalized, then quickly cut the holes in the architectural model to synchronize the two.
Tie ‘em Together with Systems
Once all of your equipment and fixtures are placed, it’s time to create the systems. It could be argued that construction modeling doesn’t really need systems, since that is really under the purview of design. However, associating elements into systems can show significant performance gains rather than leaving them in the default system. Although I won’t typically wire up the electrical devices, I will create circuits based on the electrical drawing panel schedules. Use the System Browser to view what elements belong to systems and which do not.
One of the best reason to use systems in construction modeling is that you can color code them with filters. By doing so you can easily cross check system integrity and identify components not in a system as well as get instant feedback when modeling out the duct and piping as to which system it belongs.
Duct Duct Pipe
Once the systems are created, it is time to model the duct and piping. Some may start piping and duct first, which is a workable option; it’s a personal preference. I like creating the formal systems first as it allows the connected duct and pipe to automatically inherit them. Otherwise you will end up with tons of systems that are created on the fly and at some point you will need to clean things up. This can be tedious and a real time waster.
When modeling duct, piping, and conduit, you need to understand how the contractor wants to install things. Talk to the job foremen for advice; they are usually more than happy to help anyone who can make their life easier. For piping, they usually like to run pairs of supply and return pipe side by side, both at the same elevation as much as possible, and rise/drop to each piece of equipment as required. Mechanical designers, on the other hand, will often run each pipe at different elevations so they can shoot off side to side easier. This takes up much more room above the ceiling, which is already at a premium.
When laying out the duct and piping, which can be tedious in and of itself, the secret is to make use of “working” sectional views and section boxes liberally through the project to isolate the condition you need to explore. I’ll create a specific Working Sections view type complete with a view template that includes my typical color-coded filters and a section tag with custom head and tail that identify them as such. I try to create as few working sections as I can get away with, to keep the Project Browser tidy, and simply move them around as needed. It’s also easy to ctrl+drag a section to make a temporary copy.
For section boxes, use the View Cube > Orient to a View to create a 3D section of a 2D working section. Additionally, use the COINS Auto-Section Box add-in, available for free from the Revit Apps store. This is super handy for creating sections by simply selecting objects: (https://www.youtube.com/watch?v=7rWdUsKyBOo)
Filters
Because of the complex nature of MEP trade modeling, ensuring your views are easy to work with is essential. You will undoubtedly make use of shaded 3D sections more than any other view type. I’ve found that the biggest help in managing this voluminous amount of material is to take full advantage of Filters.
Pipes all look the same, so you need to be able to visually distinguish between steam condensate and domestic cold water. While you can use system types to provide the graphic override, it’s tied to that one parameter. Filters allow you to key off of almost any MEP property. Apply them in the Filters tab of the View/Graphics Overrides dialog box and color code them by overriding the Projection/Surface Pattern with a colored solid fill. The additional use of transparency and cut pattern overrides for architectural elements also really helps view things easily in dense areas.
As suggested in Part I of this series, I highly recommend formulating a standard color scheme for all of your systems. Create a 3D view with all of the filters working. Then, just as with the RVT links, create a view template that only overrides the Filters tab, and apply the same template to all of your 3D views.
I tend to keep everything turned on in the Model tab in all views, then use Filters alone to selectively turn things on or off as required. Managing the bulk of your visibility requirement via Filters is often easier than in the Model tab as you can combine categories into a single filter—e.g., including pipes, pipe accessories, pipe fittings and pipe insulation—and it works across linked models.
Figure 12: The service tunnel view’s View Filters
Modeling Level of Detail
Level of Development (LOD) is an AIA term that is supposed to govern how much is modeled for a specific purpose. In reality the use of LOD in construction is so vague I consider it useless. It certainly does not dictate how much effort you put into your modeling tasks.
Instead I go for the minimum level of detail I can get away with. Remember that you are modeling mostly to identify clashes, so you won’t need or want every nut and bolt. Follow the age-old aphorism that everything should be made as simple as possible, but no simpler. The best rule of thumb is to always start by under-modeling the family. It is expensive to model details that are unnecessary, and curved surfaces are tough using the anemic modeling tools in the Family Editor. Get the basic size correct with the connectors working; if you want more detail, add it later. Chances are, you won’t.
MEP Shop Drawings
Finally, you will need to create shop drawings for fabrication. This is where Revit really shines, even in its current form, because you can leverage all of that BIM data to easily tag and notate things. You will want to create multi-faceted tag families that can report different parameters, such as duct size, length, top and bottom elevation, and so on.
Figure 13: A partial HVAC duct shop drawing. All of the tags and text notes are intelligently reporting data from the model elements.
Conclusion
The future of Revit for MEP coordination and fabrication is very bright. Even without any special add-ons, you can leverage the power of the Revit platform for MEP trade contractor modeling right now. With the promise of Autodesk’s Fabrication suite of applications coming to the Revit platform, get ready for easier, more accurate MEP modeling, simpler cost estimating, and a direct model-to-shop floor fabrication workflow in the near future.
