Running Mains and Vent Piping in Revit MEP: BIM 321 Course Tutorial

Welcome back to the CAD Teacher VDCI video course content for the BIM 321 course, Introduction to Revit MEP. In our previous session, we systematically cleaned up our model components to prepare for waste piping installation. Now we'll advance to running the main lines—a critical step that establishes the backbone of our drainage system before connecting individual fixtures.

Our strategy involves running the mains first, then methodically tapping all connections into the system. This approach mirrors real-world construction sequencing and ensures proper coordination between floors. Let's begin by establishing our route to the second floor. I'll select this section view and optimize its scale for better visibility—reducing the size slightly to achieve the ideal working resolution.

To properly orient our view for pipe routing, I need to rotate this section for optimal pipe visibility. Using the RO command (rotate), I'll click anywhere in the view, drag the cursor, and execute a precise 90-degree rotation. This positioning gives us the sectional perspective necessary for accurate vertical routing.

Now I'll expand the view to encompass the entire pipe run, ensuring we can see all connection points and elevation changes. After deselecting the current elements, I'll close any hidden windows using the ribbon command—this maintains a clean workspace essential for complex MEP coordination. Double-clicking enters the section view directly, preparing us for active modeling.

For optimal workflow efficiency, I prefer using the WT command (window tile) to establish my preferred layout: plan view on the left, section on the right. This configuration, while personal preference, allows for simultaneous horizontal and vertical coordination—a best practice when routing building systems across multiple floors.

Now we'll begin the actual system routing. I'll run this system vertically, then horizontally to capture all required connection points efficiently. Using the PI command (pipe), I'll start with our waste piping system and establish a 4-inch diameter—appropriate for main trunk lines in commercial applications.

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Moving to the section view, I'll select the starting connection point and drag upward. Notice how Revit automatically adjusts the diameter to 6 inches when connecting to the existing pipe—this intelligent behavior requires manual override to maintain our intended 4-inch sizing. I'll correct this to 4 inches and proceed with the vertical run.

Here's where we encounter slope requirements—critical for gravity-fed drainage systems. While we haven't drawn sloped pipes in section view previously, our slope settings remain active at 1/8 inch per foot. This is the industry standard for pipes 4 inches and larger, while pipes 3 inches and smaller typically use 1/4 inch slope (1/4 inch over 12 inches). When drawing horizontally in section, observe how the pipe automatically slopes upward as we extend the run—this built-in functionality ensures code compliance.

I'll draw horizontally to approximately this position, maintaining the proper slope gradient. After hitting escape to end the command, we can see that Revit has automatically generated the appropriate fittings—a significant time-saver that also ensures proper connections.

This brings us to an important discussion about fitting selection and specification accuracy. Notice we have a standard tee with a reducing coupler—functional, but not optimal. Industry best practice calls for specific reducing tees that provide cleaner connections and better flow characteristics. Let me demonstrate by selecting this pipe fitting and examining our type selector options.

The limited selection highlights the need to load additional families. I'll access the load family command and navigate to Pipe > Fittings > PVC > Schedule 40 > Socket Type. Within the DWV (Drain, Waste, Vent) folder, we'll locate the "Tee Reducing Sanitary"—a specialized fitting designed specifically for sanitary drainage applications.

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After loading this family (without placing it immediately), I can now select our existing tee and change it to the sanitary reducing tee via the type selector. This creates a much cleaner, more accurate connection that better represents field installation practices—a crucial consideration for constructible BIM models that guide actual construction.

Proper venting represents another critical system requirement that must extend through the roof assembly. I'll select the main line and use the plus sign to convert our connection to a tee configuration. From this point, I'll route a dedicated vent line—typically 2-inch diameter for residential applications—straight up through the roof structure. This vent provides essential air circulation that prevents trap siphonage and ensures proper drainage flow.

Applying the same fitting optimization principles, I'll change this connection to our tee reducing sanitary fitting, creating the same clean, professional connection we established below. This attention to fitting detail may seem minor, but it significantly impacts model accuracy and constructability analysis.

With our main lines established and vent piping properly routed through the roof assembly, we've created the essential infrastructure for our drainage system. Our systematic approach—running mains first, optimizing fittings, and ensuring proper venting—reflects professional MEP design methodology.

Let's pause here to consolidate our progress. In our next session, we'll focus on the first floor connections, systematically tying all fixture rough-ins into this main trunk line. This methodical approach ensures proper system integration and maintains the high standards expected in professional BIM coordination.

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