piping

How the system works

Tubing made from PEX, or cross-linked polyethylene, has quickly become the norm in residential construction.

A flexible tubing, PEX is joined using brass or plastic elbows and tees that are made watertight with a copper compression ring that is squeezed over the joint.

Indoor environment Quality- Low to moderate

There were many concerns about potential health effects from PEX piping when it was launched, and it was not allowed for use in potable water systems in some jurisdictions until the early 2000s. A number of studies since have found no direct health effects from the use of PEX tubing in potable water systems, but there are claims that standard testing does not necessarily include elements or compounds that may be unique to PEX. Some types of PEX are made with bisphenol A (BPA), a controversial organic compound that may pose health risks. PEX tubing is nonetheless considered safe by all national, state and provincial governments and standards associations in North America.

Environmental impacts: High

The petrochemicals used to make high-density polyethylene have a wide range of impacts from harvesting, including habitat destruction, ground and surface water contamination and air pollution.

The manufacturing process requires significant amounts of heat and the use of toxic compounds, with impacts including air pollution and water contamination.

Embodied Energy: high

Waste: moderate to High

PEX offcuts are not recyclable and must be sent to landfill. Offcuts can be minimal, because the material comes in long rolls and can be cut exactly to required lengths.

Cost: Low

PEX is by far the most affordable option for supply-side plumbing

Labour Input: Low

The ability of PEX to bend around corners without requiring joints greatly reduces labor time, as single runs of pipe can be used between fixtures and trunk lines. Where joints are required, the compression rings are fast to install and require little skill and no heating equipment.

Durability: moderate

PEX is expected to be quite durable, though it has not been in use long enough to have proven itself in the field over decades. It is prone to degradation in sunlight, and must not be run in exposed locations. There were early issues with failures of brass fittings at joints, and of damage from contact between certain brass formulations and PEX. These issues have been addressed in recent years.

PEX has an upper temperature limit of 90–140 °C (195–285 °F), depending on the type of tubing. It is typically not used to attach directly to hot water tanks, flash heaters or solar hot water systems.

How the system works

Polypropylene tubing is not nearly as common as PEX, and many types of polypropylene are not rated for potable use. However, some manufacturers produce certified plumbing tubing from polypropylene, a type of thermoplastic polymer resin. It has been more widely adopted in Europe over the past few decades, and is only just finding its way into the North American market.

High-grade polypropylene is formed into lengths of tubing. Elbows and tees are also polypropylene, and are joined using heat fusion. This process uses relatively low heat on both sides of the joint and pressure to bond the two sides together, resulting in joints that are solid and continuous, with no unlike materials or weak points.

Polypropylene tubing may also be used on the waste/drain side of the plumbing system, where it is by far the most sustainable option.

Indoor environment Quality- moderate to high

Polypropylene is considered a non-leaching plastic, with approvals for potable use. It is considered the least toxic of the food-grade plastics and does not contain bisphenol A (BPA). Its high melting point makes it stable even for hot water piping.

Some green building programs recognize polypropylene piping as the least toxic option available and will reward its use with points in scoring systems.

Environmental impacts: Moderate to High

The petrochemicals used to make polypropylene have a wide range of impacts from harvesting, including habitat destruction, ground and surface water contamination and air pollution.

The manufacturing process requires less heat input and chemical processes than other plastics, but still contributes to air and water pollution.

Embodied Energy: Moderate

Waste: moderate

The tubing and connectors are fully recyclable, even once fused.

Cost: high

As a relative newcomer to the North American market, polypropylene is more expensive than other potable plastic pipe. This is likely to change as it is more widely adopted.

The fusing tools required for joints are an investment that must be made in order to use polypropylene pipe.

Labour Input: Moderate to High

Polypropylene pipe is faster to install than copper but slower than PEX, as it is not flexible enough to turn sharp corners and requires more fittings, with each fitting taking longer to install.

Durability: Moderate to high

Over the past three decades in Europe, polypropylene pipe has proven itself to be very durable. Its main marketing angle is increased durability over metal and other plastic pipe, due in large part to the fused joints. 

Polyvinyl chloride (PVC) pipe is used widely in DWV and septic systems. This plastic is rigid, slightly brittle and is biologically and chemically resistant. It is more UV-resistant than many other plastics.

The manufacturing process for PVC is intensive, and it is singled out by many environmental organizations as the most problematic plastic due to its high chlorine content and the dangerous by-products that result from its manufacture and degradation. Vinyl chloride is a known carcinogen, and high levels of cancer among workers involved in PVC manufacturing are attributed to exposure.

On the job site, PVC piping is joined using a glue that is highly toxic to installers, containing tetrahydrofuran, methyl ethyl ketone and cyclohexanone. The vapors disperse relatively quickly, but in manufacturing, use and disposal of this product is very problematic.

PVC recycling programs exist, and will often accept piping offcuts.

Polypropylene pipe is a relatively recent option in North America, gaining acceptance in many codes in the past decade. See supply-side pipe description above.

Polypropylene is the best choice among the plastic piping options for DWV, as

Most of what is still commonly called cast iron pipe is actually ductile iron pipe, which largely replaced cast iron in the 1970s and ’80s. This type of pipe usually has a polyurethane or cement mortar lining on the inside to help resist corrosion. The exterior of the pipe may be coated as well (often with plastic) when the pipe is buried. This type of pipe is not typically used in residential DWV systems, but is an accepted solution in most codes. It may not be available in some of the smaller diameters commonly used in residential plumbing.

Iron pipe is manufactured from largely recycled metal content, but the process is still energy-intensive, requiring high heat input. The cement and/or plastic linings and coatings are also high-impact materials.

Iron pipe is fit together on-site using flanges and bolts or spigot and socket connections. Both rely on an elastomeric gasket and/or sealant to prevent leakage. Pipes come in pre-determined lengths with flanges or sockets cast in, making on-site fitting clumsy and time-consuming.

The cost and weight of iron pipe, the slow fitting process and the potential for leakage at joints are all drawbacks for this option. For a homeowner attempting to make a plastic-free home, the nature of the gaskets, sealant and pipe linings must be considered.

Iron pipe is recyclable.

Galvanized steel pipe with threaded joints and fittings is an accepted solution in most codes for DWV uses in a building, but not for buried lines. This type of pipe was commonly used on supply-side plumbing for many decades, but is no longer supported by codes because of corrosion issues.

Steel pipe is manufactured from largely recycled metal content, but the process is still energy-intensive, requiring high heat input. The galvanization process typically involves dipping the steel pipe and fittings into molten zinc, a second heat-intensive process. The zinc coating helps to inhibit corrosion.

Galvanized steel pipe is fit together on-site using threaded couplings, elbows and tees. Pipe comes in standard lengths, but can be cut and threaded on-site where custom sizing is required. This is a labor-intensive process, and is avoided whenever possible. Threads are wrapped in Teflon tape or “pipe dope” to prevent leakage.

The cost and weight of steel pipe, the slow fitting process and the potential for leakage are all drawbacks for this option. For a homeowner attempting to make a plastic-free home, it is nonetheless the best option available.

Steel pipe is recyclable.

Vitrified clay pipe (VCP) is allowable by some codes for use as a drainage pipe for sewage systems and weeping beds, but not as a DWV solution.