Best Pipes for Domestic Underground Plumbing

“Should I have it exposed or covered”, it’s a common question we ask ourselves as individuals or as plumbers, when planning the plumbing system for a new house or that new project you are trying to get done. Both have their benefits, both have detriments and risks. But ultimately, any choice made should be by personal preference or by certain factors considered. Underground (Covered) plumbing will be the focus of this article; choosing the right plumbing material to be buried underground both by soil or concrete and considering various factors that may affect what type of pipe you’d require.

underground pipe

According to added research and our own personal preferences, domestically, PPR pipes can be best used for minimal underground supplies such as; a singular house or a small group of houses. A PPR pipe is a type of polypropylene plastic that has some advantage over other plastic pipes used in residential plumbing. Their joints are made by heat fusion welding rather than glues; they have high resistance to leakages, are highly stable and durable. For large supplies, metallic alloys supposedly stainless steel is required. It is very similar to PPR pipe supply, except it is used to convey massive flow rates at once, materials are made from steel and they are more expensive.

ppr pipes

ppr pipe to be covered

For waste control and disposal pipes; domestically, PVC pipes are best to be used underground for waste. A PVC pipe of proper wall thickness between 2.5 – 3mm can withstand imposed load for overhead soil, lateral soil pressure, possible vibrations and mechanical impact from external sources. They convey waste seamlessly from point to another. To convey larger volumes of domestic waste at once. HDPE pipes can be used as they pose similar resistance to external impacts and are effectively corrosion resistant.


Hence, including the above mentioned; this following are the pipes that can be utilized for underground plumbing categorized by supply and waste:

Supply PipesWaste Pipes
PVC pipesPVC pipes
CPVC pipesCPVC  pipes
Copper pipesPP pipes
PEX tubingGalvanized pipes
PP pipesCast iron pipes
Brass pipesHDPE pipes
Stainless steel pipes

Factors in Choosing a Pipe Type for Local Underground Plumbing

Magnitude of Supply & Discharge

The quantity of liquid to be conveyed however large or medial determines the type of pipe you’d need for supply or waste discharge. Domestic supply lines can supply number of housing units varying from one to tens of houses or an entire town, however necessary. The amount of water conveyed if heavy, requires a pipe type strong enough to withstand water weight and pressure. Using a pipe material such as a 1 inch PEX tube for water flow of 50 to 80 psi would be terrible. Materials such as steel would be majorly ideal for large underground supply, PPR pipes can then be utilized for smaller underground supplies.

However, for waste discharge, typically PVC pipes are mainly implemented for small units. Combining housing units or having discharge for a large group of houses or a community would require the use of HDPE pipes. Cast iron or galvanized steel can be used although they are liable to rust and are quite expensive. Concrete pipes are just extravagant. Using a material too stiff for waste can backfire because movement of soil due to seismic activities can damage or break pipe. Drainage pipes are mostly buried deep due to its content and required slope.

Depth of Pipe from Ground Surface

Certain factors determine how deep the pipe is meant to be from the ground level. With regards to supply, it is either just the need of protecting pipe from damage, prevent obstructions or for aesthetic reasons. For waste discharge, foul water pipes are underground mostly for hygienic reasons and due to slope level for pipes. The depth of pipe affects the decision of type of pipe required for supply. Pipes too close to the surface would be exposed to partial loadings from soil and imposed loads. Having the pipe 2 feet and beyond would be ideal for soil to deflect mechanical loadings. However pipes too deep into the ground might be exposed to seismic activity which in turn will cause damage to underground pipe. It’s a factor to consider although supply pipes in most cases aren’t meant to go beyond 2 feet beneath the ground level. For personal preference, if supply pipe is to be placed within 1 – 2 feet, material should be strong enough to withstand any possible weight within the domestic area.

Chemical Reactions with Earth Minerals

Aggressive soil conditions in certain cases will cause pipe to degrade, mostly by corrosion, an exposure to soil moisture and strong chemical compounds react negatively to certain materials. Metallic alloys in most cases, concrete pipes get affected when there is high acidity within soil however plastic pipes do resist this form of damage.

Contacts from soluble chloride salts found in soil or water typically causes corrosion to metal surfaces. The severity of the corrosion is determined by the amount of moisture in soil, conductivity of the solution, the oxygen concentration within the soil and pH of the solution. Each metal degrades when exposed to specific element or compound present within soil. Going through research before installing a waste discharge or supply line underneath soil can be hectic; choosing plastic pipes is therefore the way the go provided supply and discharge lines don’t convey liquids with harmful objects or extreme temperatures.

Internal Water Pressure

The flow rate of contained liquid usually tests the resolve of pipe materials, majorly at the joints. You have to ensure that material or pipe type preferred has to possess strong fittings or an adequate method of fusion to prevent leakages or damage to pipes from pressure of water. Heat fusion for PPR pipes can withstand a sustainable amount of pressure. Usage of pipes that utilize glue or rubber to remain firm can be effective although they are not advisably the best. For larger supplies, steel can be used because their joints are also firmly welded. For waste lines; within domestic regions, pressurizing the liquid is rarely required. Slopes are mainly used to each flow of conveyed liquid.

Joe Taylor

Over 2 decades of remodeling experience, Joe is an expert in home improvement. He is now the Managing Editor of PlumbJoe where he writes guides for homeowners. His hobbies include climbing, running and playing the piano.

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