To Earn a Plumbing Permit, Head Back to the Drawing Board

Q: DEAR TIM: My city allows homeowners to install their own plumbing. To get the permit, I need to supply a rough-in plumbing diagram. What is a plumbing diagram? Can I just do a bathroom plumbing diagram? All I am doing is adding a bathroom. Is it a good idea to include a bathroom plumbing vent diagram? -- Dave B., Cincinnati

A: DEAR DAVE: You should count your blessings that you live in a community that allows you to do your own work. Some areas of the nation do not allow owners of single-family homes to do their own work. I happen to be a master plumber, among other things, and certain homeowners can do better work than some of the plumbers I have seen in my years in the field. If you can install the piping correctly, and it meets or exceeds the plumbing code, why shouldn't you be allowed to do the work?

A rough-in plumbing diagram is a simple isometric drawing that illustrates what your drainage and vent lines would look like if they were installed but all of the other building materials in your house were magically removed. You would see the pipes in three dimensions and be able to see all of the connections, pipe sizes, fittings and vent piping.

By drawing the lines that represent each pipe at certain angles, you can make a three-dimensional drawing on a flat piece of paper. This is simply a matter of perspective. Imagine looking at your house's plumbing system as you hover in the air at an angle instead of just looking at your house from the front door. This is what a rough-in plumbing diagram looks like.

A plumbing diagram is a useful tool that can save you lots of money and headaches. The drawing communicates to the plumbing inspector that your system will meet the code. When you apply for your permit, an inspector studies your rough-in plumbing diagram to make sure that the pipe sizes are correct and that you are using the correct fittings at the places where pipes connect.

For example, imagine you think it is acceptable to install a fitting connecting two drainpipes at a 90-degree angle and that this pipe is in the ground under a concrete slab. In almost every jurisdiction I know of, this is an illegal connection. You draw this, and the plumbing inspector corrects the mistake before you install the pipe and later have to rip it out to make the correct connection -- using two bends to make the 90-degree turn.

You should have to do only a bathroom plumbing diagram for your job. It would be unreasonable for you to have to make a drawing of your entire plumbing system, especially because it is hidden behind the walls. You will be expected to show how and where your new drains will connect to your existing plumbing system. This is important, as the branch line you install must connect to an existing drain in the right location.

The diagram will have to include bathroom plumbing vents. Vent pipes on plumbing diagrams are drawn as dashed lines, while pipes that carry water are drawn as solid lines. You will need to show how and where your new vent pipe connects to an existing vent pipe or exits the roof as a separate vent. If you are going to go through the roof with this pipe, be sure it is sized correctly to prevent getting choked with ice. This can happen in periods of severe cold weather if the pipe exiting the roof is too small in diameter.

Be sure you call out the size of each pipe shown on your rough-in plumbing diagram. Show all changes of direction correctly. If you intend to use a fitting that turns a hard 90-degree angle, show that on your drawing. If you intend to use fittings that turn just 45 degrees, draw those acute angles on the paper.

Tim Carter can be contacted via his Web site, http://www.askthebuilder.com/printer_Submit_Question.shtml.

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