Polybutylene piping or PB, is a form of plastic that was commonly used in older homes for water supply piping in 1978 up until around 1995. It was used mostly because it was inexpensive, easy to install, and more flexible unlike most rigid piping such as copper. It can usually be identified by its grey color, although sometimes can be a dull white or blueish grey. Easiest way to know if you have PB piping is to look for "PB2110" that is usually stamped onto the piping.
Issues with Polybutylene
Multiple studies have been done that have found that certain disinfectants in water can react with the polybutylene and cause it to deteriorate from the inside out. Causing the pipe to start to flake inside and eventually make its way to the exterior of the pipe causing it to leak. This issue could easily go unnoticed in the crawlspace or in between drywall and cause major water damage or even mold. Lawsuits have even been filed since the 1980's claiming defects in the manufacturing of the pipes resulting in millions in dollars in damage.
Although homeowners are not required to replace polybutylene piping, it is highly recommended. Replacing the homes plumbing can be costly, but it could actually save you money if the piping were to fail and cost you more money in water damage and property damage to the home. Homeowners can also run into issues with insurance companies if the home still has active polybutylene piping because it puts the home at risk of property damage.
Given all this information, older homes with polybutylene piping should not make you turn or run away from your dream home but do your own research of the history of PB piping to be aware of the risk. However it is a good idea to have an inspector and plumber thoroughly evaluate the current status of your home's plumbing, talk to insurance companies about polybutylene piping, and consider replacing or working out a deal to replace the homes plumbing to avoid any issues, leaks, or water damage in the long run and cost you more money down the road.