Q: My town has recently started allowing plastic waste-pipe instead of cast iron in residential construction, and a lot of my competitors are making the switch. What are the big differences between the two kinds of pipe?

A: PVC PLASTIC, ABS PLASTIC, and cast-iron drain and waste pipe are considered equivalent in most jurisdictions within the U.S., although a handful of municipalities still cling to older code rules favoring cast iron. Any of the three materials can do the job, explains plumbing engineer, licensed plumber, and code consultant Julius Ballanco. But there are some differences that might lead a builder to prefer one to the other. Cost, appearance, weight, strength, labor considerations, and availability could all factor into a builder's decision.

PRICES AND DISCOUNTS

“Plastic pipe is a lot cheaper to purchase,” says Ballanco. Price hikes for PVC have narrowed the gap, and cast-iron suppliers say it adds up to only $150 per bathroom. But Ballanco says complex discount structures mask the actual comparison.

“A typical plumber's discount on cast-iron pipe could be anywhere from 25 percent off up to 45 percent off list price,” Ballanco explains. “Smaller guys get 25 percent off. Bigger guys doing thousands of feet get 45 percent off. But if they use plastic, they can get up to 75 percent off list price. So, if cast iron is listed as four bucks, big plumbers pay $2.50 a foot. If plastic is listed as a dollar a foot, they really pay 25 cents a foot. You see the difference?”

EASY AS PIE: Complex joints and fittings like this are quick and easy to assemble with PVC  pipe and special adhesive.

EASY AS PIE: Complex joints and fittings like this are quick and easy to assemble with PVC pipe and special adhesive.

Home-center pricing further complicates the picture. “Any consumer can look up the list price of plastic. If they shop at a big home center, they will pay less than half—like 35 percent or 40 percent of list price. ... But if you look up cast iron's list price, a home center will charge you close to that list price—if they will even sell you cast iron, which not many do.”

PERCEIVED QUALITY

So why would anyone pay extra for cast iron? Ballanco says that cast iron carries a customer perception of higher quality. “I try not to jump into that fray,” he says. “But one issue is that PVC pipe can look ugly when it's exposed in a basement.” The white pipe shows dirt, and the purple primer applied at joints can drip and streak. “ABS pipe, which is black like iron and uses no primer, actually has greater consumer acceptance than PVC.”

LIMITED VISIBILITY: Adhesive joints for ABS plastic drainpipe are not as visible as the purple  adhesive used with PVC. However, the two types of pipe function equivalently, and  the choice is usually based on availability.

LIMITED VISIBILITY: Adhesive joints for ABS plastic drainpipe are not as visible as the purple adhesive used with PVC. However, the two types of pipe function equivalently, and the choice is usually based on availability.

Noise is another issue, Ballanco notes. “I've gone into a few new McMansions where, to get the drain from the master bath down into the basement, they have run pipe across the living-room ceiling. Here these people just spent $750,000 on a house, and whenever somebody upstairs flushes, people in the living room hear a whooshing sound coming across the ceiling.”

The greater mass of cast-iron pipe largely silences the rushing sound of a flowing drain. Major supplier Charlotte Pipe and Foundry Co. (www.charlottepipe.com) coined the phrase “Quiet House” for its hybrid drain-waste-vent (DWV) system, which couples cast-iron drainpipes to PVC vents. But a thoughtful floor plan can allow waste pipes to be located at the back of a closet or in an out-of-the-way partition. “And if you're going to run plastic up in the ceiling,” says Ballanco, “throw in some unfaced fiberglass batt insulation, and you'll be amazed at how much it deadens the sound.”