PEX is relatively new material (less than 20 years) that has gained widespread acceptance in the new construction piping and building renovation repiping for potable water systems.

The reasons are obvious – PEX has flex. The material is inexpensive AND the installation is fast and simple.  PEX is especially desirable on repipes since it can greatly reduce the size of the wall intrusions as plumbers can snake the material across smaller openings.

Unfortunately, there are some vulnerabilities that the owner needs to be aware of so that they can specify the right PEX components for their specific job.  Keep in mind that contractors are only liable for workmanship, manufacturers are liable for material defects, and the owner is liable for everything else. While we would always recommend obtaining a professional engineering opinion, this short article will help the owner understand what PEX is and how to manage the big vulnerabilities to using PEX: brass fittings, UV exposure, water quality, and even vermin!.

Cross linked Polyethylene – advantages

Cross Linked Polyethylene is a modification of polyethylene plastic commonly found in children’s playground equipment.  Cross linking means that the individual ‘mers’ in the ‘polymer’ are bunched up into knots instead of aligned in direction.  This allows the material to return to its original size and shape after being stretched.  This is great for holding on to fittings, bending around corners, and expanding under pressure, heat, or even freezing conditions.

PEX is very fast to install and can be threaded through walls without having to necessarily cut out large sections of wall board.  Connections can be visually inspected with great reliability and precise measurement is not a critical as materials such as copper or CPVC.  PEX has been widely used for several decades with broad acceptance in the market and universal familiarity in the plumbing trade.  Many different companies support the PEX products with accessories and connectors such as manifolds, hangers, and specialty adapters.

Preventable Problems With PEX

PEX is clearly not without its own problems, fortunately these may be avoidable. In the engineering profession, we understand that it is rare for one single problem to cause a failure, rather, it is the combination on two or more problems that lead to the major accidents. Many times accidents occur when one party does not communicate with another. With PEX, the owner, contractors, builders, maintenance personnel, etc, must be aware of the system configuration and have a plan for interacting with the system.  For this reason, engineering counsel is often warranted in a complex system.

Dezincification:

Brass is an alloy of copper and zinc.  When the zinc content is too high, it can corrode away under certain water conditions leaving a weak and porous copper shell, which can lead to failure conditions ranging from persistent leaks to a rare breach of a pressurized line.    At least one class action lawsuit was filed against the makers of a particular brass fitting that was failing in service causing substantial property damage.  The root cause was found to be the dezincification.

Most of these defective fittings were found in big box hardware stores and made cheaply overseas.  This suit was settled for 90 million dollars or so and the problem is now easily avoidable. Other problems have been found in areas with high mineral content such as Nevada and Hawaii. The owner should specify low zinc brass fittings or use ‘engineered plastic’ fitting components.

Dezincification in the Pacific Northwest

Coengineers recently conducted a more extensive analysis for a condominium association in the Pacific Northwest.  One interesting feature that we encountered was strong disagreement in the engineering community whether dezincification presents a problem in the Pacific Northwest or not.  In cases of suspected dezincification in the PNW, it may be prudent to perform a limited test. If there are currently no leaks, it is important to only disturb the minimum amount necessary to identify the composition of the zinc used in your system, then watch and maintain the system. A case study for conducting due diligence may be found here.

Chemical leaching

PEX was also suspected of leaching controversial chemicals such as MBTA, TBA, BPA, and other chemicals that are considered toxic. While we cannot testify to the truthfulness of this claim, the State of California has banned PEX in many building structures.  Given the segmented nature of permitting jurisdictions in the US, it would be wise to be aware of these concerns.

It is generally accepted that of the three types of PEX (called type A, B, or C), type B is the only formulation that does has not been suspected of any leaching considerations.  As such, a leaching concern is easily avoidable (given proper attention to other considerations such as strength and temperature ratings among the 3 varieties). Owners should be diligent to specify the type of PEX that is being installed.

Ultraviolet Radiation:

The stabilizers in PEX are highly vulnerable to breaking down under UV radiation – while some sources may claim that some UV exposure is acceptable, we advise that all precautions should be taken to shield this material from UV rays. Even fluorescent lamps and CFLs are to be avoided especially where ceiling route may interact with recessed fluorescent lighting. There are many shielding products available to solve this problem. However, PEX is best suited in total darkness. 

Agressive Water Chemistry:

PEX is also known to be slightly vulnerable to chlorinated water and possibly copper ions resulting from copper corrosion upstream.  The temperature rating of the water must be strictly adhered to. Alone, these factors may not be worrisome in many application, however when combined with the the other aggravating factors, the aggressiveness of the water may amplify hazard potential.  

Externalities:

Most builders will shield a PEX installation from a future owner or contractor, say, hammering a nail into the wall.  For this reason, the homeowner should be aware of the potential to cause a leak by intruding through the wall with a nail or saw. Some contractors will use a thermal measurement device to identify water piping before cutting into a wall for any other reason.  It is important for the owner to know where the pipes are before cutting into a wall.

We have seen several instances where mysterious leaks appear in PEX installation corresponding to the extermination of rodents.  The poison that is often used to kill small animals causes them to become very thirsty and seek water.  Rats appear to be especially clever and can discern the sound of water flowing through PEX pipes – then rapidly chew through the PEX to access water.  Make sure that ALL hired contractors – from electricians to exterminators – are licensed and experienced when interacting with a building that has a PEX system.

Conclusion:

It can be seen that failures will most likely occur from the combination of two or more seemingly unrelated problems.  It is rare that any single person or contractor is aware – on a scientific basis – of all these factors and the way that they can interact with each other.

Further, The owner or maintenance personnel cannot be expected to know all of these details – they just install what they buy at the supply shop.  It is important that the owner stay aware of these vulnerabilities of PEX and watch the installation closely.

A vigilant owner will hire an engineer to oversee the specifications and construction