A pressurised water pipe can go anywhere: over a beam, under a duct, as long as it stays tight. A gravity drain cannot. It has to fall continuously towards one point, and a few millimetres lost on one segment is where the water sits.
Revit pipe slope is therefore where drainage parts company with supply: pick the right system, switch the slope on before the first click, and read elevations from the bottom of the pipe rather than its centreline. This article builds one sanitary run in Revit 2027: the slope table, a sloped run, fixture connections, fixing a slope drawn the wrong way, and tagging the invert on the drawing. Supply pipework is covered in how to draw pipes in Revit; to build a full water and drainage model on a real sample building, the Institute runs a Revit MEP course.
How drainage differs from supply
Three differences drive the way you model.
Slope is compulsory. Supply pipes are drawn level, drains are not. In Revit the slope is a parameter of the segment, set before you draw or edited afterwards.
Elevations are read at the bottom. Pipes hang on threaded rod cut to the underside of the pipe, so the number on the drawing has to be the invert. Revit calls the inside bottom of the low end Lower End Invert Elevation.
Gravity drainage sets out first. Because it cannot dodge up and over, the gravity run is usually fixed first and the other services route around it. Dividing the ceiling void between systems is covered in MEP shop drawings.
The slope figure itself comes from the design, not from Revit. For buildings in Vietnam the design standard in force is TCVN 4474:1987 for internal drainage; clause 2.2 sets the diameter and the minimum slope of the branch from each sanitary appliance in its Table 1. Revit simply carries out the number you type.
The file and the slope table
You need a floor plan of the level, a linked architectural model and drainage pipe types in the file; Revit MEP sample files explains where to get the Institute's sample file to follow along.
Before drawing, open Manage › MEP Settings › Mechanical Settings › Pipe Settings › Slopes. This is the list of slopes Revit will offer while you draw. The Institute's sample file carries twelve: 0; 0.3; 0.5; 0.7; 0.8; 1.0; 1.2; 1.5; 2.0; 2.5; 4.0 and 100 %.
If the design slope is not on the list, click New Slope and type it. Revit warns you if the value is steeper than 45°.
Set up the pipe before the first click
Step 1. Open the plan and start the Pipe command. Systems › Plumbing & Piping › Pipe, or type PI.
Step 2. Choose the drainage pipe type. In the Type Selector pick a plastic drainage type such as uPVC. The type decides which fittings appear at the turns; building your own type is covered in pipe types in Revit.
Step 3. Set the diameter. Type 110 into Diameter in the Dimensions group. Revit fills in Outside Diameter 110.0 mm, Inside Diameter 99.4 mm and Wall Thickness 5.3 mm from the segment table.
Step 4. Set the elevation. Drainage on this floor usually runs under the slab, so the elevation is negative: type −200 into Middle Elevation.
Step 5. Choose the sanitary system. Scroll the Properties palette to the Mechanical group and set System Type to Sanitary. After you draw, Revit names the system for you, for example Sanitary 1, and the pipe takes that system's colour.
Draw a sloped pipe from branch to stack
Step 6. Switch the slope on. On the Modify | Place Pipe tab, the Sloped Piping panel has three buttons: Slope Off draws level, Slope Up draws uphill, Slope Down draws downhill. Click Slope Down and pick a value in the box beside it, for instance 2.0000%.
Turn on Show Slope Tooltip as well and Revit shows the start offset, the current offset and the slope next to the cursor as you draw.
Autodesk's Draw Sloped Pipes page lists three ways to apply a fall: the ribbon buttons while drawing, the controls on a segment already drawn, and the slope editor for a whole system.
Step 7. Click the start point, then the end point. The first click is the reference end: with Slope Down the far end ends up lower. Draw from the high end towards the low end, that is from the furthest branch back to the stack, the way you would sketch a tree from twig to trunk.
Step 8. Read the segment back. Select the pipe and Revit puts the numbers on screen: the elevation at each end, the slope box with a triangle showing which way it falls, and the size at both ends. The segment below is 5.8 m long at 2%, so the two ends differ by exactly 116 mm.
To change it, there is no need to delete and redraw. Click the elevation box or the slope box on screen and type a new number. Click the triangle and Revit swaps the reference end, which reverses the fall while holding one end where it is.
For a whole system, select a pipe and use Modify | Pipes › Tools › Slope to open the slope editor. On the same tab, the Offset Connections panel decides how a connection is made when two pipes sit at different levels: Add Vertical keeps the slope and adds a vertical piece, Change Slope connects straight and ignores the slope.
Connect fixtures into the sanitary system
Step 9. Connect the water closet. Select the fixture; the ribbon shows Modify | Plumbing Fixtures. Click Connect Into on the Layout panel. The Select Connector dialog lists the connectors with their sizes; pick the drainage connector, click OK, then click the sanitary run. Revit draws the connecting pipe and inserts the fitting where they meet.
Step 10. Use wyes rather than square tees. Branches on drainage join with a 45° wye or a swept tee so the flow stays smooth. Which fitting appears is a property of the pipe type: open its Type Properties, go to Routing Preferences and set the wye family under Junction.
Step 11. Draw the vent. A vent is drawn exactly like a drain but with Slope Off, since it needs no fall, and with the system type of the venting system in your file. For the vertical part, change Middle Elevation mid-run and click Create Riser, or draw it in a section where you can see the rise.
Read the invert elevation, then tag it
Step 12. Read the elevations in Properties. Select a sloped segment and the Constraints group lists them all: Upper End Top Elevation, Upper End Centerline Elevation, Lower End Centerline Elevation, Lower End Bottom Elevation, Lower End Invert Elevation and Slope.
On the segment shown: top of the high end −145.0 mm, bottom of the low end −371.0 mm, invert at the low end −365.7 mm, slope 2%.
Step 13. Set the spot elevation to the bottom of the pipe. Go to Annotate › Dimension › Spot Elevation. On the Modify | Place Dimensions tab, the Display Elevation box offers four options: Actual (Selected) Elevation, Top Elevation, Bottom Elevation and Top & Bottom Elevations. Choose Bottom Elevation.
Step 14. Three clicks per tag. Click the pipe, click again to set the shoulder of the leader, click a third time to place the text. Do it at both ends of the segment: a sloped pipe gives two different numbers, +5.39 m and +5.48 m in the image below.
One number for a whole sloped segment is wrong at one end at least. To combine the invert with the size and the system name in one label, add the parameters to the tag as described in tags in Revit.
From CAD to Revit
On CAD the slope is a line of text beside the pipe and the invert is typed in by hand at each end; change the run and all three have to be changed, and one of them is always forgotten.
| Task | On CAD | In Revit 2027 |
|---|---|---|
| Slope | a note in text | a parameter of the segment; change it and the model follows |
| Invert | typed at both ends | computed from centreline elevation, diameter and slope |
| Level symbol | a block with attributes | Spot Elevation set to Bottom Elevation |
| Wyes and bends | blocks placed by hand | generated from the pipe type's Routing Preferences |
| Clashes with beams and ducts | a section drawn by hand | sections cut from the model, checked with Interference Check |
The drafting work disappears; in exchange you have to declare the pipe type, the system and the elevation before you click.
When the slope will not behave
| Symptom | Cause | Fix |
|---|---|---|
| The pipe is nowhere on the plan | It runs under the slab, outside the view range | Adjust View Range, or check in a section |
| The pipe comes out level | Slope Up or Slope Down was not pressed before the first click | Select the pipe and type the slope into the on-screen control |
| The fall runs the wrong way | The first click is the reference end | Click the direction triangle beside the slope box |
| The slope is lost when connecting | Change Slope is active | Switch to Add Vertical to keep the fall and add a vertical piece |
| Display Elevation is greyed out | The view is at Coarse or Medium, so the pipe is a single line | Set Detail Level to Fine and place the spot elevation again |
| The design slope is not in the list | It is not in the Slopes table | Mechanical Settings › Pipe Settings › Slopes › New Slope |
Three things you often hear
| What you often hear | What Revit 2027 actually does |
|---|---|
| The slope is typed on the Options Bar | 2027 removed the Options Bar; the three slope buttons and the value box are on the Sloped Piping panel |
| The level on the drawing is the centreline | Centreline is the default, but Spot Elevation has a Bottom Elevation mode, and setting Vertical Justification to Bottom makes the elevation you type an invert |
| Fixing the slope afterwards is the same thing | It works, but segments already connected to fixtures drag their fittings along; settle the slope before connecting |
In short, revit pipe slope work is four linked moves: fill the slope table, set the sanitary system and the size, switch Slope Down on and draw from branch to stack, then tag the invert at both ends of every segment. If the discipline is new to you, what Revit MEP is sets out the three M–E–P systems first.
Frequently asked questions
What slope should a drain have?
Whatever the design and the applicable standard require; TCVN 4474:1987 sets the diameter and minimum slope of the branch from each appliance. Revit only carries out the number you type.
Draw from the fixture outwards or from the stack inwards?
Draw the main run first and branch towards the fixtures. The branch then inherits the elevation and size of the main, which saves editing twice.
How do I reverse the fall without deleting the pipe?
Select the pipe and click the direction triangle beside the slope box. The reference end swaps and the slope value stays.
What is the difference between bottom elevation and invert elevation?
Lower End Bottom Elevation is the outside of the pipe, Lower End Invert Elevation the inside; they differ by one wall thickness, 5.3 mm on uPVC D110.
Why can I not pick Bottom Elevation for a spot elevation?
The view is at Coarse or Medium detail, so the pipe is drawn as a single line. Switch Detail Level to Fine and all four options become available.