Avatech Tricks: Creating Dormer Roofs in Revit Building

11 Jan, 2006 By: Craig R. Thomas Cadalyst

Revit Building helps you create dormer roofs, including the dormer geometry required by the opening in the main roof.

Adding a dormer is easy if you don't care about overlapping geometry or what the interior might look like (figure 1). But we usually do care about such things. The following steps will help you create the dormer components and also create the opening in the main roof that corresponds to the dormer geometry.

Figure 1. Interior with overlapping geometry (left) and roofs trimmed and opening created (right).

Creating the Dormer Geometry
1. In any elevation view add a new level that represents the top of the dormer walls and the level where you will draw the dormer roof. Also, we will assume that you have a level named Roof that corresponds to the main roof (figure 2).

Figure 2. Elevation view with the Dormer level added.

2. Make the Roof level the current view.

3. Draw three walls out in front of the main roof to form the dormer walls. Set the top of the wall to the Dormer level (figure 3).

Figure 3. Dormer walls.

4. Now open the Dormer level view.

5. Add a roof by footprint to the dormer walls.

    a. Use a 1' offset and make sure the Defines Slope box is checked for the sides of the roof (figure 4).

Figure 4. Roof lines that define the slope.

    b. Use a 1' offset and uncheck the Defines Slope box for the front of the roof (figure 5).

Figure 5. Front roof line.

    c. For the rear line, use the Lines tool and draw a line 2 or 3 feet from the front roof line, but not all the way back to the end of the dormer walls (figure 6).

Figure 6. Back roof line.

    d. Trim the side lines back to the rear line.

    e. In the Roof Properties (figure 7), set the Rise/12 property to a shallower slope (try 4").

Figure 7. Rise/12" property.

    f. Select Finish Roof.
Attaching the Dormer to the Main Roof
At this point, your model should look something like figure 8. Next we will move the roof into place over the main roof and attach the top of the dormer walls to the two roof objects.

Figure 8. Dormer geometry before being attached.

1. In the Roof Level view, move the dormer over the main roof (figure 9). Snap the face of the front dormer wall to the face of the wall below.

Figure 9. Moving the dormer geometry into place.

2. Use the Join Roofs tool to trim the dormer roof to the main roof. Notice that you are able to select the back edge of the dormer roof because it is not buried within the main roof (figure 10).

Figure 10. Joining the dormer roof to the main roof.

3. Select each of the dormer walls. Click the Attach button on the Options bar. Make sure the Top button is selected and pick the dormer roof.

4. At this point, the parts of the dormer walls that are not directly beneath the dormer roof are down at the dormer level. That may or may not work for you, depending on your design intent. If this portion of the wall needs to attach to the main roof, follow the remainder of this step. If not, you may skip this step.

    a. Open the dormer level view. Hide the main roof. This should expose the dormer walls below.

    b. Draw a reference plane that passes through the intersection of the dormer roof and the dormer side walls (figure 11). Split the dormer walls along that reference plane line.

Figure 11. Reference plane that intersects dormer roof and side walls.

    c. After the spilt, you should be able to select both newly created side walls (figure 12). Change to the Roof Level view and attach these walls to the main roof.

Figure 12. Side walls after split.

Cutting the Hole in the Main Roof
We're almost ready to cut the opening in the main roof. But first, we need to check that the dormer walls are connected properly at the front of the dormer.

1. Select the front wall and look at each end. If it isn't the same, as in figure 13, the opening may not be symmetrical.

Figure 13. Check to make sure the ends of the front wall are the same.

2. Use the Edit Wall Joins command on one end to get it to match the other. It should look like figure 14 when you're done.

Figure 14. Symmetrical front wall.

3. Now we're ready to cut the dormer opening in the main roof. Open the 3D view. On the Modeling tab in the Design bar, select the Opening command. Select the Pick a Roof to be Cut by a Dormer Opening option (figure 15).

Figure 15. Select a placement option.

4. Select the main roof (figure 16).

Figure 16. Main roof selected.

5. You'll notice that your only option at this point is to pick either a wall or a roof.

    a. Pick the dormer roof (figure 17). Two lines appear that represent the intersection of the main roof and the dormer roof.

Figure 17. Two lines represent the intersection of the main roof and the dormer roof.

    b. Now pick a side wall (figure 18). A line representing the intersection of the side wall and the main roof is drawn.

Figure 18. The line represents the intersection of the side wall and the main roof.

    c. Pick the remaining walls (figure 19). Again, a line is created representing each intersection between the wall and the main roof. Unlike most sketches in Revit, you do not need to trim these edges to each other.

Figure 19. A line represents the intersection between the wall and the main roof.

    d. Select Finish Boundary.

You're done! I've inserted a small window in my dormer wall (figure 20). Now that the opening is created, you can copy it and all the dormer geometry (walls, windows and roof) to other locations on the roof.

Figure 20. Completed dormer roof.

Of course you can do many variations on this theme. The front dormer wall does not have to line up with the wall below. Try creating the dormer roof as an arc (roof by extrusion) in elevation. Let your imagination run wild!

About the Author: Craig R. Thomas

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