Well thought out plumbing drawings are often, but not always, required to obtain a building permit. An understanding of how to produce plumbing drawings that show the right information is critical for your new home or renovation project in order to get your permit the first time and avoid a series of schedule killing resubmissions to the Building Department. Clear and accurate drawings also help during the building inspection process should disagreements arise. Fortunately, a little due diligence and some guidance is all that is needed to produce these drawings.
Check with the building department where the project is located to get their requirements for plumbing drawings. If you feel that the requirements are beyond your skill to produce, hire an engineer or architect to produce the drawings for you. Also, some building departments require the drawings to be produced by a design professional anyway. Verify this requirement before you put pencil to paper and you may save a lot of time and aggravation.
Draw the plumbing plan. The plumbing plan is similar to the floor plan of the house, but highlights the plumbing fixtures (usually in bold.) The plumbing plan will show the hot and cold water routes to each fixture, waste lines from the fixture, and the size of each pipe. Use different line types for hot, cold and waste. One method is to use a dashed line with the letter "H," "C," or "W" about every half inch to distinguish the different lines. Another common linetype designation uses a long dash with one short dash for cold, a long dash with two short dashes for hot, and a solid line for waste. Special symbols are usually used to show valves, elbows, and other specific devices. There are common symbols used in the industry, but the exact symbol used is not important as long as there is a clear and accurate legend explaining all special symbols on the drawing. Be sure to show your line types in the legend as well. The plumbing plan is typically done to a standard drawing scale, so choose a scale that works with the size of your paper.
Draw the plumbing isometric. A plumbing isometric is a little more difficult for people that are not used to technical drafting. An isometric is a type of three dimensional representation of the plumbing system. Use notes to call out the pipe sizes between each fixture, and after each branch drain line joins the main line. You should also call out the pipe size of the vent lines, including the size of the line through the roof. To visualize this drawing, imagine that you have removed all of the walls from the building and that you are viewing it from above one of the roof corners.
In this drawing, scale is not as important as relationships. The intent of this drawing is to give a three dimensional representation of the entire system. Often, this drawing is broken up into two drawings, one showing the supply lines, and one showing the waste and vent system. Sometimes it is only required to show the waste and vent systems in this drawing. Again, consult the Building Department for their requirements.