Should PEX Piping Be Insulated?

Pex Pipe Lg

PEX pipes is present in nearly all new home construction and plumbing pipe replacements done today. Insurance companies report that over 250 million homeowners annually have property damage from busted water pipes, many caused by frozen pipes.

PEX has become the piping of choice by plumbers because the piping polymers allow it to flex, making installation easier. PEX is lightweight and can bend, reducing the number of connection joints. Many debates that because the piping has flexing properties, it doesn’t need insulating. Does PEX need to be insulated?

You should insulate PEX piping exposed outdoors or inside uninsulated spaces like a basement, attic, or crawl space. The polymers in PEX can flex slightly with temperature changes where rigid CPVC, PVC, or copper can’t. However, PEX tubes can still freeze and burst when temperatures drop below 20 degrees Fahrenheit.

While PEX pipes can and will freeze in cold weather, they withstand cold temperatures better than rigid pipes like copper, PVC, or CPVC, which can freeze and burst. Manufacturers of PEX piping won’t provide a guarantee against the pipes bursting at freezing temperature.

As a general rule of thumb, if your PEX piping is traveling through interior walls or insulated exterior walls, you don’t need to insulate it. However, piping exposed outside or inside unconditioned spaces like a basement, crawl space, or attic should be insulated, mainly if you live in cold-weather areas.

While PEX is growing in popularity due to its unique and adaptable features, it is not invincible. There has been plenty of confusion regarding the standards and requirements for ensuring optimum efficiency, longevity, and safety.

Stick around to determine the fundamentals of insulating PEX piping compared to other piping materials and how you should approach the insulation process following manufacturers’ and professionals’ recommendations and guidelines. 

Should PEX Piping Be Insulated 

Yes, insulation is an essential part of installing PEX piping, as the lack thereof could lead to unfortunate outcomes. It is more resilient against fluctuations in temperatures than other commonly used materials. It’s flexible pipes and does not act as a conductor for heat and cold as easily as metal materials do.

PEX piping is still vulnerable to cracking when:

  • it’s not shielded effectively from freezing temperatures falling below 20 degrees Fahrenheit
  • long-term exposure various ultraviolet light sources 

Ensuring that the PEX piping has protection from these threats prolongs its longevity while still benefitting from its ability to contract and expand with cold, heat, and even water flow and pressure.

Insulating PEX piping also decreases the risk of potential functional failures due to moisture condensation and promotes energy efficiency. Limiting the exposure risks and insulating reduces water pipes’ chances of bursting or leaking and causing tiresome and frustrating outcomes, which may be costly to repair, not to mention the potential necessity for piping replacement. 

PEX Pipe Insulation Requirements

Another critical factor to consider is that the standards and requirements are applicable across all piping types, whether copper, CPVC, PVC, or PEX.

  1. ASTM Standard Requirements and Sizing for PEX Piping

PEX piping is generally available in standard sizes ranging from ¼ to 2 inches, at a length of 50 to 200 feet. It’s crucial to calculate the pipe’s size with the amount of insulation that will be necessary. According to the American Society for Testing & Materials, the standard for PEX piping is CTS, which is also the standard for copper pipes and CPVC. 

You can insulate PEX piping with the same foam insulation sized for copper, commonly found in home improvement stores. The standard IPS sizing is effective for insulation, but the fit would not be as snug due to incorrect size.

Trapped air space commonly plays a role in various insulation techniques. This approach would be efficient enough and may add additional insulation based on this principle. Select the right piping insulation size for a proper fit.

  1. Type of Material for Insulation of PEX Piping

Foam is usually the recommended type of insulation for PEX piping, as it meets the flexibility levels that such material demands. Since PEX is flexible pipes, the insulation needs to be flexible too. Fiberglass insulation is far more rigid and would not accommodate such tractability. 

  1. Type of Fit for Insulation of PEX Piping

Once the correct insulation material has been identified, the appropriate type of insulation will need to be chosen. Persons can select between a continuous length and polytype, which have various features and benefits for users.

While the continuous length type can be useful for PEX pipe, which spans over an extended area, polytypes are generally better suited to PEX flexibility and are easier to apply post-construction. 

Continuous Length Type: This insulation is a full-length tube with no openings of necessitated closures, which offers thorough and even insulation across the entire length of the PEX pipe.

While this would undoubtedly be beneficial, this is more commonly used during the building’s construction phase, as you can slip it over the PEX piping before being installed within the building.

Utilizing a continuous length type of insulation will not be practical post-construction unless the PEX pipe is removed and disconnected entirely or if the insulation is cut, which may defeat the purpose of selecting the continuous type. 

Foam Pipe Insulation: This insulation is far more practical and simpler to apply since it is flexible. 

An opening on one side is the most practical for installing post-construction insulation, particularly for odd spaces, tight corners, and event tees.

The PEX piping should be clean before insulating, as it may not allow the adhesive to seal well. 

The PEX piping should be covered by the insulation and fitted snuggly by pushing down the insulation until the pipe pops into place. After insulating, seal off the opening by pulling off the protective strip to reveal the adhesive. You would then push the seams together to seal the insulation completely. Many professionals also use contact cement to join the ends of insulation lengths for further durability.

How to Insulate PEX Tubing

Plan Where PEX Pipes Are Run

Insulating a new home involves proper planning. It’s good to route hot water pipes through interior walls rather than exterior walls where possible. The heat from your home can prevent hot water pipes from freezing.

When outside temperatures are 20 degrees or lower, keep your interior temperature much warmer, keeping your internal pipes from freezing.

Insulate PEX Piping Exposed Outside

Sometimes, having hot water pipes outside can’t be avoided. Cold water pipes must run to exterior spigots (hose bibs) or other uses such as tankless water heaters. Any PEX pipes exposed outdoors need a minimum of R3 (3/8″ thick) pipe insulation. Some colder climates require an R4 (5/8″ thick) or higher pipe insulation.

Insulate all exposed PEX pipe and secure the pipe inspection in place with tape along seams and bends where pipe insulation is loose.

Open an Interior Faucet During Freezing Temperatures

When a hard freeze occurs, generally 25 degrees or lower, it’s a good idea to open the cold water tap on an interior faucet to allow the water to dribble out a small stream of water. Flowing water won’t freeze as easily or as quickly. This also reduces water pressure on the walls of the piping.

Winterize the PEX Pipes in Vacation Homes

If you have a secondary vacation home, you don’t visit in the winter. You should consider winterizing the plumbing. Winterizing the plumbing includes draining the entire system, including the water heater and toilets. The cold won’t hurt the plumbing system when water is not present. Also, insulate the plumbing P traps under sinks and inside crawl spaces or basements.

PEX Piping in Basements and Crawl Spaces

During winter, unconditioned spaces like attics, crawl spaces, and unfinished basements are particularly vulnerable for PEX piping. These spaces are not heated or insulated like the inside walls, which can cause the pipes to freeze if it gets cold enough.

Your hot and cold water supply lines (as well as your PVC drain traps) need insulating in unfinished spaces. Often, these pipes freeze and crack along connection joints. PEX will expand about 1 inch to 2.5 inches per 100 feet for every 10-degree temperature change, which can help prevent some damage. However, in short spans of PEX pipe, freezing and cracking can and likely will still happen.

Insulating the hot side will assist in delivering hot water to fixtures quicker, and the water inside the pipe cools at a slower rate. The cold water side may condensate in the summer, contributing to damp crawl space conditions.

PEX Piping in Attics

When installing insulation for PEX piping in an attic, the most challenging part is the tight spaces, sharp corners, hangers, joists, and tees running across the area. PEX and foam insulation will provide enough flexibility to cope with such factors, coupled with open insulation on one side.

There are varying approaches for applying the insulation, such as trimming it and running it from the opposite end for tees, mitering the insulation at elbow curves, and securing the ends with cable ties for extra hold and support for the adhesive.

PEX pipes in the attic are susceptible to fluctuations in climate and temperature as they are more exposed to outdoor conditions. Both the hot and cold lines should be insulated effectively, as insulation of the hot side will assist in delivering hot water to the load faster. In contrast, the cold pipe insulation will lower the risk of condensation forming in summer, which may cause seepage through the ceiling. 


Insulating PEX is fundamental for establishing a highly functional plumbing system with optimum efficiency. Taking the time to invest in this crucial process will be a fantastic investment in the long run. Having PEX pipes coupled with proper insulation will ensure that the piping is protected during freezing temperatures.


Hubert Miles | Licensed Home Inspector, CMI, CPI

Hubert Miles is a licensed home inspector (RBI# 2556) with more than two decades of experience in inspection and construction. Since 2008, he has been serving South Carolina through his company, Patriot Home Inspections LLC. As a Certified Master Inspector, Hubert is dedicated to providing his expertise in home inspections, repairs, maintenance, and DIY projects.