New Best Practices for Plumbing
The plumbing transition to Autodesk® Revit® has some challenges stemming from a history of good drafting practice. That's not to say Revit does not respect good drafting practices, but the software focuses more on how plumbing will be installed rather than how it is easiest to read on a two-dimensional drawing. Historically, plumbing has been represented diagrammatically to improve drawing clarity while minimizing the number of views required. While Revit is very good at representing pipes and valves precisely where they are, it struggles a bit at being diagrammatic. This is where we need to remember this isn't your father's drafting table. Understand why "this is the way we have always done it," and ask yourself if the reasons are still relevant.
There are some diagrammatic practices on floor plans that are not necessarily still relevant in Revit. Let's start with a simple example of line spacing. Let's look at a typical 1/8" scale domestic water plan. Traditionally, cold and hot water lines are drawn nine inches apart. This is to allow room for nine-inch-tall text (in model space) to be legible, without overlapping the opposite line work or text. Installed, if the pipes are each a half-inch diameter with two inches of insulation, then really they should be modeled about six inches apart. By separating them further, we are not being efficient with the allotted space, and we are potentially creating false clashes in the model. If we have cold and hot water, throw in a hot water return line, fire protection main, and a gas line, the problem is compounded several times over. Now, consider it would take two five-inch pipes with two inches of insulation to equal a nine-inch separation. Diagrammatically it isn't a problem to show things offset, but this example illustrates that it is not good practice to model it like we did when we were drafting. We are not drafting anymore, we are modeling.
Figure 1: Needed spread
Figure 2: 9-inch spread
Breaking from tradition, why are we restrained to 1/8" scale? Historically, it was because we only wanted to "show it once." When we were hand drafting, we only wanted to represent objects one time so we didn't need to correct multiple views upon making a single change. Also, we didn't want to make larger scale views and add more sheets to the drawing set, adding to labor and material costs. These practices survived the CAD transition for drafting, as the principles behind them were still valid and, in fact, we were still drafting.
Figure 3: Overlapping view ranges
Figure 4: Overlapping section
I don't believe they are valid when modeling. In Revit, the "show it once" mentality is no longer relevant. It is one element regardless of the number of views in which it shows. You model it once, but show it as many times and ways as you need. Should you need to make a change, all the places it is shown are updated, because it is the same element. Using a larger scale will perhaps add additional sheets to the set, but the time needed to manage the additional sheets is negligible compared to the days of hand drafting. So that argument also does not hold water in my opinion. Finally, arguing that minimizing sheet count minimizes printing costs is also outdated. Most drawings are exchanged electronically now days, either as PDFs, DWFs, Navisworks® or Revit models themselves. Furthermore, I would argue that using a larger scale stays true to the traditional drafting principles of clarity and readability. It does so by providing a drawing that is clear to read with less clutter.
Now let's turn our attention to traditions on waste and vent drawings. Most show the waste below the level, and the vent in the plenum space above. (insert Overlapping View Ranges & insert Overlapping Section) Well, the plenum space above also has a waste line in it for the floor above. The waste line serving the floor above is also in the same view range as the vent line for this floor. We need a way to differentiate between the waste on the current level and the waste serving the floor above while sharing the same view range. There are several solutions to this. Creating separate worksets for each level and using a filter to isolate only the piping pertinent to the current level is one solution, though there is significant effort required to maintain the accuracy of which elements are on which workset. One trick that helps there is not to have one workset per floor, but to use odd and even worksets. That reduces the needed number of worksets to three, odd, even, and common. If you are using this method be sure to pay close attention to the pipe rise drop symbols—they can easily get confused if you have one portion split between two worksets.
Another way around this complication is to create one waste view and one vent view. Place the vent view over the waste view on the same sheet. If the two views are using the same scope box, then Revit will assist you with placing the second view by providing an alignment guide vertically and horizontally. There is one drawback to this approach: the pipe gap settings do not get applied when the vent line crosses over a waste line. It helps to have good differentiation between the line types as does printing to PDF with a good line merge setting. Annotating these views can get tricky as you don’t see the elements and annotation from the other view. If you are working directly on the waste view, you won’t see the vent lines and corresponding annotation. If you open the sheet and activate a view to annotate, you see the elements and annotation from both views.
Figure 5: Vent links kicked out
Our next traditional practice is also on the waste and vent plans. Traditionally they show the vent line risers kicked out at a 30° angle so that you can see the lines more clearly. (Vent Lines kicked out image here) The 30° angle does not represent what will actually be installed. It is there simply to improve clarity. One of the strengths of Revit is drawing sections and 3D views. Well, include enough sections and 3D views to provide the clarity needed, but model it accurately. I am suggesting that any areas where the plan view is not sufficient, include a section or two and an isometric view. It takes little to no time to generate and place them on the sheet, so why not?
The last topic I want to touch on is riser diagrams. They may resemble the piping systems designed, but the pipe lengths, fixtures, and actual connections do not represent how it will actually be installed. It is just a diagram, after all. In Revit, a skewed view at 30° NE will give you a view that resembles a riser diagram, but then there will be areas where critical piping is hidden by a gang toilet or some other obstruction. Traditionally the piping would just be stretched until the obstruction was out of the way, but in Revit, stretching the piping around would ruin your floor plans.
With a few simple tricks, riser diagrams can be better in Revit then they have ever been before, while actually using the piping from the model. (insert Riser Diagram image here) The riser diagram shown is composed of three duplicated 3D views with different scope boxes on each, showing different areas. Then place each onto the same sheet in relatively the correct locations. Now you can stretch the gang toilets out of the way by moving the 3D view. You can add some continuation squiggles to your views where the lines appear to end, then maybe add some drafting lines with a hidden line type. Then add pipe tags and fixture tags that will actually update as the design changes. You have your same old riser diagrams that are now built from the actual piping used in your model. Regrettably, there is still an issue with the pipe gap setting being ignored on 3D views. If this is causing you trouble, my only suggestion is to break from the traditional single-line riser diagram and show it double line. As double line, you still don't get a pipe gap, but the closer pipe does hide the pipe in the background where they overlap. For domestic water, show the insulation as well increasing the hidden portion of pipe. This makes for a good-looking set of riser diagrams that are much clearer and accurate than traditional.
Figure 6: Riser diagram
Perhaps it isn't that plumbing has more challenges with transitioning to Revit as it does to transitioning to modeling. Some of our drafting practices are becoming outdated. Perhaps some can adapt, some may need to be pruned, but I don't think any are immune to change. Also recognize the opportunity to improve our craft. With the improvements to Revit's sloped piping and system calculation abilities, plumbing is making a giant step up from traditional 2D drawings. Sure, modeling is different from drafting, but it does not mean we must sacrifice the traditions of quality and clarity in our drawings.
