Water Pipes: Polypropylene, PEX-AL-PEX and Copper

Polypropylene, multilayer and copper pipes compared for home water supply: jointing methods, hot water suitability and concealed installation.

Water pipes are among the first things to disappear inside walls or screed during a renovation, and replacing them usually means tearing out the finishes. So the choice of pipe material deserves more thought than "which is cheapest". In apartments and private houses three options come up most often: polypropylene, multilayer (PEX-AL-PEX) and copper. Each has its own logic and its own risks.

Polypropylene pipes

Polypropylene pipes are joined by heat fusion with a special welding tool. A properly fused joint becomes one body with the pipe, which is why this system is widely used for concealed runs in walls and screed.

Strengths:

• joints are permanent, so there are no nuts to loosen over time;
• the material does not corrode and resists scale build-up;
• fittings are widely available in a broad range.

Points to consider: hot water lines need reinforced pipes with an aluminium or glass-fibre layer, not plain ones, because polypropylene expands considerably when heated. Joint quality depends directly on the installer's experience: an overheated joint narrows the bore, while an underheated one lacks strength. The pipe is rigid, so every change of direction needs a fitting, which increases the number of joints.

Multilayer pipes

A multilayer pipe consists of a thin aluminium layer between two plastic layers. It can be bent by hand or with a bending tool and holds its shape, so long runs need fewer fittings.

There are two jointing methods: threaded compression fittings and press fittings. Compression fittings are tightened with a nut and may need re-tightening over time, particularly after temperature cycles. For that reason they are not recommended inside closed walls; press fittings are preferred for concealed work. A press fitting is crimped with a dedicated tool and cannot be undone.

The weak point is poor preparation of pipe ends. A crooked cut or skipped calibration can damage the O-rings. Bending tighter than the manufacturer's minimum radius creases the aluminium layer.

Copper pipes

Copper is regarded as long-lived, resistant to heat and pressure and reliable in hygienic terms. It is joined by soldering or press fittings. It also looks good when left exposed, which is why it is sometimes chosen for classic interiors.

Copper has its own demands. Material and installation are expensive and labour-intensive. Connecting copper directly to other metals, such as galvanised steel, can cause galvanic corrosion, so transition fittings must be chosen carefully. Water chemistry also matters; where water is very acidic or aggressive, ask a local specialist how copper will behave.

Concealed installation and pressure testing

Whatever the material, a few general rules apply to hidden pipework:

• keep the number of joints inside walls or screed to a minimum;
• run hot water pipes in insulation or corrugated sleeving to reduce heat loss and allow for expansion;
• record the pipe routes with photos and a dimensioned drawing;
• pressure-test the system before the walls are closed and write down the result.

During the test the line is filled with water, pressure is raised above working pressure and the gauge is watched for a set period. A pressure drop indicates a leak somewhere.

Which to choose

There is no single right answer. For concealed runs in apartments, polypropylene or multilayer with press fittings are both common; multilayer is convenient for manifold systems, underfloor heating and routes with many bends; copper is worth considering when longevity and exposed installation matter. The quality of the joints and a properly conducted test count for more than the pipe material itself. It is also important not to mix pipes and fittings from different manufacturers within one system.

Before deciding, ask the installer a few questions: how much experience they have with this system, which tools they use, how they will run the pressure test and how they will record the location of hidden joints. Clear answers often tell you more than the brand name on the pipe.

Zaferoğlu İnşaat plans water supply pipework together with the rest of the renovation in apartments and private houses. Tell us whether the pipes will run in walls, in the screed or exposed, since that decides a lot between the three materials.