How to plan a Drain Waste Vent (DWV) system
Things You'll Need
- Plan for the job
- building permit
- Hand saw or power saw
- eye protection
- latex gloves
- de-burring tool (knife)
- Pipe cutters
- Measuring Tape
- Felt-tipped pen
- Forstner bit to match the outside diameter of the pipe
- PVC pipe (1-1/2" to 4" depending on the type of stack)
- PVC elbows (various)
- PVC tees (various)
The most important step of building a DWV system is the design stage. Every sink, tub, toilet and drain needs to be vented to the outside through a vent stack. If you are adding a new sink, such as for a wet bar or for a bathroom expansion, then it is important to know where the current waste pipes are. In newer construction, DWV pipes are primarily made of PVC pipe. In older homes, pipes may be constructed of cast iron or copper.
Once you have drawn the plans, most local governments require that the homeowner file the plan and obtain a building permit prior to starting the project. Building inspectors like to be able to correct any basic problems in the design before any pipes are installed that may need to be removed and re-worked. From my own personal experience, it is always better to partner with your local inspector. He/she wants you to succeed. They have seen it all - from excellent work, to installations that are downright dangerous.
I have been able to save many steps and several hundred dollars by talking with my local inspector before submitting the plan for a permit.
Check with your local county, township, town or city for requirements.
Create a list of parts. I always refer back to the plan before I make a trip to my local building supply store. By accurately measuring out how much straight pipe you need, as well as counting how many fittings you need, you will be able to save gas, time and money.
A helpful tip is to locate your equipment (drill bit, measuring tape, eye protection, saw, etc.) before going to the store.
It is helpful to buy an extra PVC joint of each type you need. I always pick up two more couplers (the straight joint) than I need. That way, if I need to make a correction, I have the parts.
Measure out all of the cuts that will be required. Remember that the joints will result in more length being added to the run.
Plan what piece will be the last assembled. This is a critical step. When measuring out the lengths, make sure that you leave space for joining the pipes together. Some wall spaces are very tight. Adding a coupling will require that there be about 1/2" extra clearance than the finished joint will require. Part of the pipe fits in the joint.
Make the required cuts to the pipes. After each cut, de-burr the pipes on the inside and out. I use a common pocket knife for this step. There are special de-burring tools especially designed for cleaning the ends of pipes. Inspect the pipe for any cracks or chips that were caused by the saw. If there are cracks, then re-cut the pipe, removing the damaged section.
Pre-fit all of the parts. Use the felt tipped marker or pencil to mark the joint and the pipe. This way, when the joint is cleaned and glued, the pieces will line up. Don't skip this step!
Start gluing the assembly together. Clean the outside of the pipe as well as the inside of the pipe with cleaner. Then coat the outside of the pipe and the inside of the coupling with the PVC glue. This glue sets up very rapidly. Make a 1/4 turn when assembling the pipes to ensure that the glue covers all of the joint.
Align the joint and the pipe to the marks made earlier.
Work from one direction to the other, remembering what piece will be the last section joined together.
If your inspector requires a pressure test, make sure to install the temporary caps. After the pressure test, you will need to cut them off and then hook the section to the main drainage system.
Let the pipes dry overnight. While the glue will set up very quickly, waiting a day will ensure that every coupling will have a great seal.
If you needed to cut a hole in the roof, try to put the vent piping hole on the back side of the roof. This will allow the vent piping to extend through the roof while keeping from detracting from the front of the house. If you do need to cut a hole in the roof, ensure that you buy the right flashing based on the roofing materials used on your house.
Congratulations! You have installed your DWV system!
Tips & Warnings
- I always use latex gloves when cleaning and gluing PVC. The gloves are inexpensive and will keep your hands from being discolored from the cleaner or become sticky from the glue.
- If you need to cut into a pipe that services another sink or bathroom, make that the last step. Nobody likes to wait to use a dishwasher or bathroom until you are done with the project.
- Wear eye protection! The cleaner and glue are hazardous to your vision. Sawdust and wood from drilling holes also may land in your eyes. Save your vision.
- DWV plumbing may not have pressure like other plumbing systems in the house. However, that doesn't mean that the system is less complex. Always ensure that you keep a minimum grade of 1/4" per foot for straight runs, and that each fixture is vented to the main stack.
- PVC solvent and glue are toxic and highly flammable. Never work around an open flame or smoke while gluing the pipes.
- Photo Credit Google Images
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