Many plumbers who joined the trade 30 or 40 years ago believe the use of plastic pipe and fittings is the best thing that has happened to residential plumbing systems in a hundred years. On the other hand, old-timers can be heard complaining that plastic has taken much of the trade out of the business, and has given everyone the idea he can be his own plumber. Is it possible that both groups are right? Probably.
Since the late 1950s, plumbers have been introduced to a wide variety of plastic pipe and fittings to be used in drainage, waste and vents systems (DWV), supply piping, and hot and cold water distribution. Some plumbers were slow to make the change from metals to plastics, but code acceptance, the ease of installation and the economics of construction caused most to accept and even embrace the change.
My father installed plumbing when pouring lead joints and threading pipe were daily chores. I joined the trade at a time when this skill might have gotten you a dollar or two more an hour, but it was no longer a requirement for earning the title of Plumber.
Today, as plastic continues to evolve, more do-it-yourselfers are attempting to install and repair plumbing systems—something most of them would not have considered doing 30 years ago. This can be both good and bad.
Home inspectors can raise the alarm
Money can be saved, and that is good for the pocketbook. On the other hand, when installers use the wrong pipe for the job, the system is more likely to fail or, even worse, the installation can be an accident waiting to happen This is where the home inspector can have a huge impact. Before home inspections became commonplace, it was unlikely anyone with knowledge of construction or trade work would look at a house after the code guy checked off or until something went wrong.
Now home inspectors often go behind amateur installers and misinformed tradesmen. They see the improperly used products, including pipe and fittings, and they can alert owners and clients to dangerous situations. As plastic pipe gets easier to install, and pipe and fittings are sold to anyone with a buck, some of the trade’s fate will move from the daily trade practitioners to homeowners.
This adds to the importance of a home inspection. But home inspectors need to be able to do more than describe the pipe they find; they need to be certain of its application. And, who knows, maybe a hundred years from now, if someone asks, “What is the best thing to happen to plumbing during the past century?” the answer will be, “home inspectors.”
Plastic plumbing, the positives and the negatives
A number of characteristics can make plastic piping material a better choice than metal for residential use. Its resistance to corrosion and many chemicals, both inside and out, is a real plus for a plumbing material. In addition, it can be formulated to physically handle any residential plumbing need, including drainage, water supply or distribution.
Plastic has low thermal conductivity and is able to maintain the temperature of fluids well; therefore, with many applications, pipe condensation can be less of a problem than with metal pipe. For example, PVC (Polyvinyl Chloride) pipe sweats less than copper when used for condensate drains. It rarely requires pipe insulation to prevent dripping water from damaging the structure. This cannot be said for copper or brass pipe.
Plastic piping is immune to galvanic and electrolytic reactions; it can be connected to metal pipe with no adverse effects. Plastic plumbing systems benefit from low friction loss, too. Along with this positive aspect and the pipe’s ability to remain free of the interior damage found in many metal pipes, in my experience, plastic drainpipes seem to stop up less and are easier to clean.
The pipe and fittings almost always cost less than metal products used for the same work. Because it is lighter than most metal products and more elastic, plastic material can be easier to handle, thereby reducing job-site injuries. In most cases, plastic material is easier to install, thus saving time, which in turn lowers labor costs. Lower material and labor costs are necessary if plumbers are to remain competitive in the home construction industry.
Is there a plastic pipe for every residential need?
The negative characteristics that can limit its use include a tendency to expand and weaken as ambient temperatures or fluid temperatures increase. Nevertheless, as long as the correct plastic material is selected for the job and the need for additional support and proximity considerations are observed, there is plastic pipe that will deal with any residential plumbing need.
As a rule, plastics will burn or melt at a much lower temperature than most metals. Because of fire and smoke concerns, plastic pipes often have more restrictions than metal pipes on clearances to heat sources and air distribution systems. In fairness to the plastic pipe industry, it should be noted that Polyvinyl Chloride (PVC) and Chlorinated polyvinyl chloride (CPVC) will not actually support combustion and are self-extinguishing once the source of the heat is removed.
Some plumbing plastics have a poor resistance to UV (ultraviolet) light and need chemical or physical protection against these invisible sun rays for a long, safe service life. Some manufacturers recommend applying latex paint or installing other forms of protection to shield pipe that could be exposed to UV light.
PVC and ABS pipe
PVC is a vinyl thermoplastic product made from chlorine and ethylene that was developed before World War II. I began using PVC pipe and fittings in the 1970s, even though it was introduced to plumbers a decade or so before. According to the Charlotte Pipe Company, PVC is the most widely used material for piping systems in the world today.
PVC resin is combined, along with stabilizers, lubricants, filler and a white pigment, to make a compound that is extruded to make pipe or is molded to produce fittings. The white color of the plastic comes from a pigment and actually helps protect PVC from UV light.
As a plumber, I often hear customers call ABS pipe and fittings, “the black PVC.” But it is truly a different animal. This type of thermoplastic is primarily a petroleum-based product. Because of this, the price varies. It has greater flexibility than PVC, but can warp when exposed to uneven heat from exposure to sunlight. The pipe is often exposed to sunlight during building construction or while being strapped to the top of a plumber’s truck for an extended period of time. Carbon black is used to protect ABS from UV degradation.
Does PVC have limitations?
PVC pipe is used for DWV (drainage, waste and vent systems), as well as for the main water supply pipe to many homes. It also is the pipe of choice for many well installers, and it is used for yard irrigation systems, condensate drains and pool installations. But it is not recommended for plumbing use where the operating temperatures exceed 140ºF. As the temperature of the pipe increases, its ability to handle pressure is reduced.
Of course, under normal conditions there are occasions when PVC drainpipes encounter water in excess of 140ºF, such as when hot water is drained from pots while cooking or discharges from a dishwasher. Because these are intermittent occurrences and the water quickly cools as it mixes with air and moves through the system, the pipe handles it well. On the other hand, if the PVC drainpipe was under pressure and carrying a steady flow of 140ºF water, failure would be likely.
PVC should not be used as hot and cold water distribution piping. Because PVC is so easy to install and can be purchased at most home improvement outlets, home inspectors are likely to find that it has been used to repair or re-install distribution pipes. Over time, the pipe will weaken and break down. Home inspectors should identify PVC pipe used in this way as a concern or defect in their reports.
Home inspectors will see several types of PVC plumbing pipe in homes. For DWV work, solid wall schedule 40 and cellular core PVC is used. Plumbers often refer to cellular core as foam core, and they use the pipe because of the material’s reduced weight and lower price. Along with the manufacturer’s information and other pipe data, the words “NOT FOR PRESSURE” are often visible on cellular core pipe. The outside diameters of both versions are the same as iron pipe. The pipe is considered an iron pipe size (IPS) product.
How is PVC rated?
PVC pipe is rated with a schedule number or a standard dimensional ratio (SDR) number. These numbers are printed along the exterior wall of the pipe. The numbers essentially identify the pipe wall thickness. As the schedule number increases, the pipe wall thickness increases. Schedule 80 pipe, commonly used in commercial work, has a thicker wall than schedule 40 pipe, which is used extensively in residential plumbing. As the numbers increase in the standard dimensional ratio (SDR) rating, the pipe wall thickness decreases. SDR 21 is thicker than SDR 26.
As noted earlier, PVC pipe should not be used as a water distribution pipe. Schedule 40 and SDR 21 pipe, however, are used for the water supply pipe to many homes. Codes generally require it be terminated no more than 5 feet beyond its penetration point of the foundation wall. SDR 21 and SDR 26 often are used for irrigation systems.
Common ABS products
Sold in 10-foot and 20-foot sections, schedule 40 ABS solid wall pipe and ABS cellular core pipe are the most common ABS products used in residential plumbing. Like the PVC pipe we see in homes, ABS pipe also is an iron pipe size (IPS) product. The ABS pipe used in residential plumbing is not to be used as a water supply or a water distribution pipe. My sources say temperature limitations top out around 160º-180º.
Occasionally, I hear home inspectors talk about lawsuits concerning ABS pipe. Between 1984 and 1990, five manufacturers of ABS pipe—Centaur, Phoenix, Gable, Polaris and Apache—allegedly manufactured ABS pipe that sometimes cracked circumferentially at pipe joints, resulting in leaks. Though I personally have never encountered this type of leak in Hampton Roads, Va., home inspectors might have clients who are seeking information on this settlement. Information is available at www.abspipes.com. It appears the filing deadline was April 24, 1998.
Chlorinated polyvinyl chloride (CPVC) is a vinyl thermoplastic material made from chlorine and ethylene. CPVC begins as PVC resin; then it goes through a process to add an additional molecule of chlorine. The end result is a product that tolerates higher temperatures and performs better in a fire environment than PVC. Also, it generates less smoke when it combusts and, like PVC, is self-extinguishing once the heat source is removed. CPVC pipe and fittings are light tan or crème-colored.
The CPVC pipe and fittings used in residential construction are generally a copper tube size (CTS) product. The PVC tee at the left side in the photo below is a 1/2-inch IPS fitting. The CPVC tee at the right side of the photo is a 1/2-inch CTS fitting.
In use since the 1960s, it has had great success as a hot and cold water distribution pipe. CPVC has a continuous use rating of 180ºF at 100 psi. Larger CPVC piping can be purchased as an iron pipe size schedule 80 product, but I find this pipe is not commonly used for residential service.
According to the Plastic Pipe and Fitting Association, unless prohibited by the locality, CPVC is acceptable for use as discharge piping for Temperature Pressure Relief Valves. On high efficiency gas water heaters that employ plastic vents and on electric water heaters, CPVC can be connected directly to the tank with the use of a metal-to-CPVC transition fitting. Installers should maintain a 6-inch lateral clearance between the flue and CPVC pipe on all other gas water heaters, and use a 12-inch metal nipple or appliance connector to connect the water pipes to the tank.
Also, unless prohibited by the locality, it can be used in return-air plenum and in a hot water circulating loop. It is not recommended for use on commercial and non-storage tank-type water heaters and, of course, it should not be used to provide electrical grounding.
Making the connections
PVC and ABS pipe are cut with a plastic pipe handsaw, electric cut-off saw or miter saw. Smaller pipe can be cut with a plastic pipe ratchet cutter and a wheel- type cutter that employs a special wheel. Specialty tools for cutting installed pipe include a leader-like tool that is fished behind the pipe, then pulled through in a sawing motion, and a tool that cuts the pipe from the inside out with a miniature, circular saw blade turned by a drill.
Once the pipe is cut, deburring and beveling are recommended. Deburring is the process of removing small pieces of pipe that cling to the inside and outside perimeter of the cut. Beveling is the process of shaving the outside edge of the pipe into a slight angle to create a better joint. I must confess, I’ve seen a lot of pipe quickly deburred with a pocketknife and, though recommended, rarely do I see plumbers bevel the end.
PVC and ABS do not require sanding before pipe and fittings are joined. In fact, sanding is discouraged. If dirt and oils are present, chemical cleaners are used to clean the surface. The recommended method for joining PVC pipe and fittings is to apply primer followed by solvent cement. The primer actually functions much like the cement. The pipe and fitting surfaces are softened by the chemicals and are solvent-welded together to create the joint. Standard PVC glue is clear.
To prime or not
Though clear primers are available, many municipalities require that the primer be purple in color so code officials can determine if it was indeed used on the joint. Joints can be put together without the use of primer, but by using it, you gain an additional level of confidence in the integrity of the connection. Unless required by the municipality, primer almost always is skipped with ABS installations. The glue is black.
With PVC and ABS DWV (drainage, waste and venting) systems, you will occasionally see joints held together with no-hub bands or similar connectors (see photo). Often, these connectors are used to make repairs and to connect unlike materials such as ABS to steel, cast iron and even other plastics. Plumbers sometimes combine plastic and cast iron DWV systems in a manner that helps reduce sound transmission. Use of the bands is common for this purpose. Old cast iron and steel traps are occasionally replaced for newer, better draining plastic traps. The bands are used here as well.
Transition glue or solvent cement is also available to connect ABS to PVC. In my area, I’m finding this specialty glue to be light green in color, but you may find clear transition glues or other colors as well. Talk to plumbers and plumbing wholesalers to learn what transition cements are acceptable in your area.
For connecting pipe and fittings under wet situations, fast-acting solvent cement is available. It is dark blue in color. Though it was created for use under wet situations, plumbers use it for quick, general repairs as well.
Cutting and cementing CPVC
CPVC can be cut in the same manner as PVC and ABS. The most popular method is to use a plastic pipe ratchet cutter. This tool is easy to use. It’s small and can be hung on your hip. When the tool is maintained, it’s unlikely to produce burrs, but, as with PVC and ABS, beveling is still recommended.
There are two common glues or solvent cements used to join CPVC pipe and fittings. The first cement is yellow in color and has its own primer. Because primer and cement are combined, there is only one step to complete a joint. The second frequently used cement is applied in a two-step process. It requires a primer to be used first, followed by cement. This cement is orange.
Pay close attention to plastic- threaded connections
Plastic-threaded connections require special attention. Many pipe and fitting makers recommend using only a tape-type pipe joint sealant, such as Teflon® tape, for threaded connections. I agree the best joints are made with this product, but other thread sealers–commonly called pipe dope or paste–deemed safe for plastic fitting use, are available. The secret to a good threaded connection demands that no thread sealer, tape or otherwise be applied to the starting threads of the fitting. Unless the first two or three threads are left clean, often the fitting will become cross-threaded and unusable.
When combining metal and plastic, it is generally best to insert plastic male pipe threads into a female metal fitting. Female threaded plastic fittings are more apt to split if excessive force is applied when making up the joint. I should note that Genova Products produces a female adapter for CPVC hot and cold water distribution systems that uses a straight thread instead of a tapered pipe thread. This helps eliminate splitting. An elastomeric washer is used so no thread tape or pipe dope is needed.
On the other hand, plumbers know that PVC plastic male fittings screwed directly into the metal housing of some water pumps often end up loose and leaking. When water pumps lose their prime, the heat generated by the pump operating with little or no fresh water causes the fitting to be overheated and it can become loose. This can be true for CPVC male adapters installed on the hot water side of the distribution system as well. Installing a metal nipple into the pump at the suction end, followed by a fitting that allows the plastic to be properly connected away from the pump is a good way to eliminate the problem.
Most home inspectors know to pay close attention to all fittings during an inspection, and to pay extra close attention to threaded connections at pumps and other potential heat-producing equipment.
Support issues for PVC, ABS and CPVC pipe
As the diameter of plastic pipe increases, the span on pipe support can be de-creased. As the temperature of the pipe increases, the span decreases. According to the Charlotte Pipe Company, 2-inch PVC Schedule 40 requires support at
6-foot intervals. The same material in 4-inch can be supported every 7-1/2 feet. However, according to the 2005 International Plumbing Code®, maximum spacing for horizontal support of PVC and ABS pipe is 4 feet.
When plastic pipe is used to deliver a product that has a wide range in temperatures, support issues such as sagging can develop. Manufacturers recommend support considerations be calculated at the pipe’s likely highest temperature of use. By using the International Plumbing Code® support numbers, the temperature considerations should be well covered.
The price of poor support
Pipe support for residential PVC and ABS is generally done with strapping, anchor straps or clamps. No matter what device is used, it should be wide enough not to cut into the pipe, installed loose enough to allow for expansion and contraction of the pipe, and installed in a manner that will keep the pipe from swaying or bouncing when in service. Improper support of DWV systems can create air pockets, unnecessary trapping and clogged drains. It can also lead to stress on the pipe and fittings, causing leaks on both pressure and DWV systems. Poor support can also cause the system to be noisy.
Overloading is common
A common mistake I find with today’s DWV systems is overloaded plastic strapping. As the strapping material ages and undergoes a few seasons of multiple temperature changes, it weakens. Once this occurs, it’s common to find broken strapping throughout the DWV system. As each section of strapping breaks, more weight is transferred to other sections, resulting in more breaks.
Home inspectors should use caution while inspecting a pipe system. Try to avoid applying any weight as you move over the drainage systems in crawlspaces or attics. If you break a section of plastic strapping, you can start a chain reaction of breaks that can leave the system sagging and leaking.
According to the International Plumbing Code®, the maximum spacing for CPVC pipe support should be 36 inches for 1/2-inch and 3/4-inch pipe. Along with actual strapping and support considerations, expansion can be a concern. According to the PPFA, a 100-foot run of CPVC will expand as much as 4 inches when the temperature increases 100º F. To allow for this, plumbers will install expansion fittings or use directional changes in the piping layout to provide relief.Rigid, flexible or both
Polyvinyl Chloride (PVC) and Acrylonitrile Butadiene Styrene (ABS) piping systems found in residential plumbing are considered rigid pipe. They usually are sold in 10-foot or 20-foot sections. Tradesmen refer to manufactured pipe sections as lengths or sticks.
Although rigid materials can be used for water supply and distribution, they have a natural advantage over flexible pipe when used for drainpipes. A rigid material drainpipe can be installed evenly and sloped without sags. When secured or imbedded properly, it's the preferred material for this kind of work.
Chlorinated polyvinyl chloride (CPVC) is primarily sold as a rigid
piping material. It is installed in crawlspaces and above the floor; however, it can be purchased in rolls and is often installed with the groundwork below slabs.
Polyethylene (PE), Cross-Linked Polyethylene (PEX) and Polybutylene (PB) found in residential properties fall under the category of flexible pipe and are generally referred to as tubing. Flexibility is one reason for the widespread use of tubing. PE and PB primarily are sold in rolls or coils. Even though PEX is equally limber,
it is widely sold today in straight sections, much like PB was sold in the 1980s and 1990s. Straight sections of flexible pipe produce a cleaner look and are used for stubs outs below fixtures.
Plumbers are able to pull flexible piping through drilled holes at much greater distances than rigid pipe and do so with the use of fewer fittings. Reducing fittings reduces the potential for leaks. Using a 100-foot or longer roll, plumbers can loop the pipe from wall to wall at greater distances below slab homes and, again, can avoid burying fittings.
Special thanks to Dewey Manus of the Charlotte Pipe Company, Lorry Ebeling and Gary Morgan of Vanguard Piping Systems, Mary Berklich of Genova Products, and T.S. Hart for his photo contributions.
Kenny Hart is an ASHI Member, Virginia State-Certified Home Inspector and Master Plumber from Hampton Roads, Va. He has been a speaker and instructor at numerous home inspector conventions. Meet Kenny at the 2006 InspectionWorld in Fort Lauderdale.