Cast Iron vs. PVC: Which Material is Right for Drainage Systems in My Building?

May 7, 2018 by Chris Drake

Cost vs. performance is often a primary debate when an owner or developer is deciding on material selection for their building. Decades ago, the debate on drainage pipe material selection was oftentimes not a debate at all. Cast Iron was the primary drainage material utilized for most all construction.

In recent times, PVC has become a very viable option for use in both residential and commercial construction. Cost and ease of use is often the justification for this selection. However, it’s important to discuss the pros and cons of each drainage piping material with the building owner before making a selection.

PVC
PVC storm drainage piping hung on clevis hanger. 📷: Plastic Pipe and Fittings Association

Below are a few discussion points that may be relevant when helping make a decision:

Durability:

Cast iron often lasts significantly longer than PVC piping when utilized in drainage systems. Cast iron piping can last several decades, if not for a century. One downside of cast iron is that it is susceptible to rusting if not maintained properly. The lifespan of PVC is harder to predict, as it’s use in drainage systems doesn’t have as long a history as does PVC.

PVC has a lower temperature limit and higher expansion rate. It is important to consider the system that PVC will be utilized in, as it is susceptible to damage at high temperatures and highly acidic wastes. Bracing and hanger support also has to be taken into consideration for PVC, as it can expand with higher levels of temperature swing.

PVC is not fire proof. It’s essential to ensure it is properly fire sealed at penetrations, as they will need to be handled differently than a cast iron penetration. Also, the use of PVC in return air plenums is not permitted.

Cast Iron Pipe
Cast Iron sanitary and vent stacks (black) for future connection by office tenant

Cost:

The cost for installation of PVC piping is significantly less than that of cast iron in construction. PVC is easy to work with; however, it does require more hangers and supports as compared to cast iron. Contractors generally prefer to work with PVC in my experience. It’s important to take note of what type of material was bid on by the contractor. If both PVC and cast iron are offered as appropriate drainage piping material, there may be a credit due to the owner.

Noise:

An important factor for building owners to consider is the noise factor. PVC piping noise is much greater as compared to cast iron, as it is less dense than cast iron piping and does not have the dampening affect as cast iron will provide. One of the biggest complaints by building tenants is often the noise created as wastewater is running through sanitary and storm piping. It is very important to bring this up to the owner during the schematic design process.

In conclusion:

It is important for the engineer to help an owner/developer understand the pros/cons with the selection of drainage material in construction.

For an owner who is considering cost as the prime factor in construction of their building, PVC will be the selection nearly every time. This is especially true for general multi-family apartment construction, where ownership will likely change frequently, and where upfront cost is most important. For owners in development of condo, hotel, hospitals, educational, and office construction, selection of cast iron over PVC should be carefully considered due to durability and noise reduction; which will directly relate to possible occupant complaints.

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Written by Chris Drake

Chris Drake

Chris Drake is the Plumbing Discipline Leader at BIG RED DOG. He received a degree in Aeronautical Engineering from Rensselaer Polytechnic Institute in Troy, NY and is a registered P.E. His professional experience includes the design of plumbing and HVAC systems in the campus, institutional, sports, federal, and manufacturing markets. His is also experienced in design/build, construction administration, and is a member of ASHRAE and ASPE. Chris originally hails from the Finger Lakes region of upstate New York. Outside of work, Chris enjoys exploring Austin and the surrounding hill country, traveling, and supporting the Buffalo Bills.