In 1968, German inventor Thomas Engle created a new, more flexible form of plastic we've come to know as PEX tubing from radiating Polyethylene (standard plastic). Arriving in the United States in the 1980's it became popularized through its usage in radiant floor heating, water supply lines, and buried applications. Pex tubing has become even more widely used because of its successful and broad applications, including underground usage. 

Advantages and Disadvantages of PEX Piping Material

Pex piping is used in over 60% of new construction for water supply systems in residential areas alone. There is a time and place for everything, as with any building material. PEX piping has strengths and weaknesses like anything else. Here is a lean overview of the Pros and Cons:

Pros:

Pex tubing is an inexpensive material.

PEX is color-coded, making them easy to work with.

Pex tubing and piping can run for extremely long or short lengths with minimum fittings required.

PEX material is highly corrosion resistant.

They are incredibly soft materials. This is an often-overlooked advantage but relevant and nice to have as a homeowner with experience in copper piping.

The average lifespan is 40-50 years.

Cons:

Not suitable or up to code for external outdoor use. They would require additional help.

PEX material isn't recyclable.  

The Different Types of PEX

The three available PEX materials include PEX A, B, and C. They are named this way because of the manufacturing process they undergo, and this is not an actual grading scale. Each PEX material is still considered a high-density polyethylene plastic (HDPE). They share the same fundamental strengths and weaknesses, but installation methods vary.  Understanding the different types of PEX is essential to know when planning your specific project:

PEX A

Pex A is the most flexible. In terms of kink resistance, it also has the most outstanding resistance. This type of PEX also withstands extremely well to cold temperatures but is more susceptible to burst pressure. PEX A is straightforward to work with for beginner plumbers. 

PEX B

PEX B works very well with both hot and cold temperatures. This makes it better to run from your hot water tank, but you will need a connecting material in between. PEX B is also less expensive than PEX A. PEX B is also susceptible to kinking, and once it is kinked, The piping cannot be repaired. This also makes it the least suitable material for extremely cold environments.

PEX C

PEX C is the cheapest of the three types, making it well designed for inexpensive repair projects. PEX C also has the most extended list of poor attributing factors.  PEX C is the stiffest of all three making it the most susceptible to cracking and breaking. This also makes it the least friendly PEX for novice and DIY'ers to work with. 

What Kind of PEX is Best Used Underground?

PEX A and PEX B are the most suitable forms of PEX for underground application, but PEX B is the best choice.  Keep in mind that all three PEX types meet every major building code requirement for several reasons. There are two organizations to resource for specific coding standards: Plastic Pipe and Fittings Association (PPFA) and Plastics Pipe Institute (PPI). 

Not only can PEX be used underground, but there is also a range of choices available depending on the project it is being used for. PEX can be installed as water lines for hot and cold temperatures, and they have even carried chemicals and sewage. PEX piping can be a better alternative to copper, PVC, and CPVC piping materials but can be used with existing systems. 

Due to the ability of PEX to expand and its flexibility, PEX A and PEX B are the premier choice when used for ALL underground applications, such as. This safeguards waterlines from bursting, which is more of a common occurrence with materials like copper, PVC, and CPVC. 

PEX can still be affected by extremely low temperatures (below 20 degrees Fahrenheit). If you are a homeowner trying to install water lines or sewage lines underground, ensure they are buried below the frost line, and the standard practice is roughly 12" to 18" under the frost line.  A shallow, improper burial can rupture connections and ruin fittings regardless of how resistant PEX is.

If this is particularly problematic because of your geographical location or you are aware of older fittings and hard piping connections, "sleeving" is an effective method of protecting newly installed PEX piping. In this instance, you will run your trouble spots through PVC piping, and the PVC pipe will act as an insulating sleeve covering your fittings, connections, and piping.

Would PVC Make a Better Alternative for Underground Application?

If you are going to sleeve your PEX piping with PVC, should you use PVC then? The answer is no. They are both durable plastics, but PVC will not withstand the fluctuations in temperature as effectively as PEX, making PEX the superior choice for underground lines. 

PVC does have strong points, which is why it has practical uses. It is cost-effective, corrosion-resistant, and durable. For underground use, PEX consistently is the chosen material by professionals over PVC. PVC is more widely used for insulating a PEX piping system because of its different strengths.

Does this make PEX Applicable for Outdoor Usage?

PEX pipe is not rated for outdoor use, and it can be used for outdoor purposes. Insulating or wrapping the piping would be necessary to ensure it will not burst from the elements. PEX is exceptionally durable to temperature change but isn't impervious to freezing and cracking.

The other factor is UV light. UV light is very harmful to PEX piping material and can reduce the overall lifespan of the pipe if used uninsulated for outdoor use. Insulation wrap will aid in the protection from freezing but can also help with UV exposure and physical damage. Homeowners, professionals, and DIY'ers can find wraps that block UV light. 

Although, PEX is more susceptible to breaking from physical damage (tree roots, natural disasters) than PVC. PEX and PVC work so well in conjunction. Use the proper materials to protect your piping if you decide to use PEX for outdoor use.

Conclusion

In summation, whether you are a professional plumber or an amateur starting your first project, PEX is the preferred material for underground applications. PEX is easy to work with, has a long life span, is corrosion-resistant, and is reasonably resistant to physical damage. 

PEX also has alternative applications. It can withstand transferring chemical usage and sewage. PEX material has also been used effectively for outdoor use when supplemented with wraps and PVC pipe insulators. PEX can even be buried in cement. In all actuality, staying away from tree roots, ensuring the lines you bury underground is under the frost depth, and insulating PEX in extreme temperatures will assure a long-lasting project. For underground plumbing projects, PEX should be your number one material choice.