PEX tubing is approved for direct burial outdoors, a practice most often necessary when running a water supply line to a house. PEX, since it can expand, resists freezing more effectively than rigid pipe, but PEX can still burst if water freezes in a line. As a result, it’s a must to bury the tubing below the frost line. The depth of the frost line in a given area can be obtained by contacting the municipality or local water company. Although an unbroken line of PEX would be ideal, dezincification-resistant brass PEX fittings or plastic PEX fittings should be used in areas known to have aggressive water or soil when a fitting is necessary. Stainless steel clamp rings are a better choice than copper crimp rings due to their increased corrosion resistance.
Residential water supply lines generally use 3/4” pipe (occasionally 1”). SupplyHouse carries PEX-B tubing in these sizes, as well as PEX-A rated AquaPEX and pre-insulated AquaPEX. Sleeving the buried PEX (in PVC, for example) shields the tubing and can make potential repairs easier. Embedding PEX in sand protects it from any rocks in the soil. Always check with all applicable local codes prior to installation.