If your home was built before the 1980s and hasn’t had any significant renovations recently, chances are pretty good that there are cast-iron drain pipes in your home. These heavy, durable pipes were a hallmark of wastewater lines for nearly a century due to the relatively low cost of manufacturing and ease of installation. Now, with lighter weight and easier-to-install materials such as PVC, plumbers rarely use cast-iron in residential installations.
In the event that you find yourself either needing to install new plumbing due to a bathroom renovation or re-route existing work during a renovation project, you may need a way to tie into the existing cast-iron piping. While a renovation is a good opportunity to update the entire line, sometimes a T into a current line is more convenient.
Before you start
Before you start, check with your local code enforcement body (municipal, county, plumbing board, etc.) to make sure that you are allowed to perform this work yourself. You should also look into any relevant permit or licensing requirements as well as any exemptions that you may need to file before beginning work. You don’t want to have to redo work after the fact because you failed to follow the legal process for plumbing work.
What you’ll need
- Reciprocating saw with blade rated for cast-iron
- Measuring tape
- PVC wye* and two 6” pieces of pipe in the same diameter. (Example: a 4” wye and a foot of 4” DWV** PVC pipe will create one T)
- Means for marking the pipe (I prefer to use a black marker, but I have seen others use white chalk, crayon or soapstone for clear marking)
- A screwdriver or ratcheting torque wrench
- A no-hub fitting in the diameter pipe you are working with (for our example, a 4” fitting). A no-hub fitting is essentially a rubber sleeve with hose clamps that can be tightened down on the pipe. They are not to be used for pressured applications but are useful for drain, waste, and venting applications.
**DWV stands for Drain-Waste-Vent and is a type of pipe that is rated for non-pressure applications. That means that it’s not used for any water delivery systems like faucets or other fixtures.
The first thing you need to do is fabricate a wye that can fit your cast-iron pipe. Using your wye and the pieces of pipe, glue two pieces into either end in a straight line, leaving enough pipe exposed to connect the no-hub fitting. In a 4” fitting, the amount you should leave exposed will be about 1 ¼” to 1 ½”. To get your cutting length, measure the full assembly (the two glued pieces of pipe and the wye) and add ½” to that measurement. Next, transfer the cutting length to your cast iron pipe and mark it appropriately. Use a pipe wrap or a piece of paper to make sure that you mark the entire diameter of the pipe for your cut. Remember to measure twice and cut once.
Cutting the Cast Iron
The very first thing that you need to do before you cut into anything is to make sure to turn off the water supply.
Now, before you cut into the cast-iron pipe, you need to ensure that it is adequately supported so that it will not fall onto your toe or another sensitive body part. You can support the pipe by strapping it to a nearby stud, making a temporary support brace using wood scraps and rope, or otherwise securing the cast iron pipe to the structure.
Next, line up your reciprocating saw blade with your measured cut lines and cut the pipe. Be sure to keep the saw aligned so that your cuts are square. Use consistent pressure throughout without forcing the tool. Use a file to clean off any burrs, and wipe the whole pipe clean with a rag.
If there is access around the entire diameter of the pipe, you can use a circular saw with a metal cutting blade in lieu of a reciprocating saw.
Preparing the assembly and assembling
Next, you’ll need to prepare the assembly that you’re installing. Do this by removing the bands from the no-hub fitting and sliding the rubber sleeve onto your previously prepared PVC wye. Fold the sleeve back on itself so that you can lift the wye into place, and then hold the wye in place while unrolling the sleeves. This should look like a straight line (more or less). Re-install the banding and tighten into place with the ratcheting torque wrench.
Now you can install any new plumbing work and tie it into the newly installed wye.
A few tips
- Be sure that your wye is faced in the correct direction for flow towards your drain. Trust us: you do not want to accidentally install your wye going the opposite direction because that means you’ll be sending all sorts of undesirable matter to places you definitely don’t want it to be.
- Hold your wye up to your cast iron cutting location before making a cut in your cast iron. We said it earlier, but it’s worth repeating: the old adage goes “measure twice, cut once,” so be sure to measure an extra time or two just so that you’re confident your cut will be correct.
- Don’t overtighten the bands. It can be tempting to really bear down on the bands for the no-hub fittings, but overtightening can cause the fitting to strain and eventually fail. Drain lines tend to be in the basement, so they can cause significant damage if there is an undetected leak.
It’s been a while since shag carpets, Soul Train, and cast-iron pipes, and it’s about time to get your plumbing into the new millennium. They don’t build them like they used to, but in at least this case, that is probably a good thing.