Copper vs Plastic Pipes: Which Should You Use at Home?

What "plastic pipe" actually means

Indoor plastic plumbing is not the grey waste pipe under your sink. For hot and cold water supply it means cross linked polyethylene or polybutylene pipe, usually white or grey, sold in 15mm and 22mm to match copper sizes and joined with push fit fittings. Speedfit and Hep2O are the names most people have seen on the side of the pipe.

The blue pipe that brings the water main into the house from the street is a different product again, a polyethylene made for burial. And copper for supply pipework is thin walled tube, joined by soldered, compression or press fittings. When people compare copper and plastic they almost always mean the pipework inside the house, so that is what this guide covers.

Copper vs plastic pipes at a glance

• Hidden runs under floors: plastic, because long lengths go in with no joints under the boards.
• Visible pipework: copper, because it looks right and does not sag between clips.
• First stretch out of a boiler: copper, because most boiler makers require it.
• Around an unvented cylinder: copper for the safety discharge, which must be metal.
• Repairs to an existing run: match what is there, or join to it with a proper adaptor.
• Gas: copper or other approved metal only. Plastic water pipe is never used for gas.

Where plastic pipe earns its place

The big advantage of plastic is that it comes on a coil. A run from the airing cupboard to a bathroom at the far end of a house can go in as one continuous length threaded through the joists, with a fitting at each end and nothing in between. Every joint is a place a leak can start, and under a floor you cannot see, fewer joints is a real gain.

It is also quicker to install, needs no flame, and flexes. Soldering copper under old timber floors carries a fire risk that disappears with push fit plastic. In a hard frost, water freezing inside plastic pipe will usually stretch it rather than split it, although no pipe likes being frozen and the fittings can still let go. Plastic also carries less noise, so the ticking and knocking you hear from expanding copper is quieter.

Where the pipe is going under floors in a rewire or renovation, plastic is what we fit in most London properties.

Where copper is still the better choice

Copper stays rigid, so it sits straight on a wall and stays tidy on long visible runs where plastic would bow between clips. It tolerates heat far better, which is why boiler makers normally ask for copper for the first section of pipework out of the appliance. It cannot be chewed by rats or mice, which in some London basements and under ground floors is a genuine concern. And it can be found with a simple detector before anybody drills a wall.

Around a hot water cylinder there is a specific rule. The discharge pipe that carries water away from an unvented cylinder's safety valves has to be metal, normally copper, because it may have to carry very hot water or steam. Plastic is not acceptable there under any circumstances. If you have an unvented system and are not sure what the discharge pipe is made of, it is worth having it looked at during an unvented cylinder service.

The downsides of each

Plastic depends entirely on its fittings being made properly. Push fit joints need the pipe cut square, deburred, fitted with a metal insert and pushed fully home. A joint pushed in only partly can hold for weeks and then let go. Plastic also must not be left in sunlight, should not be buried in plaster without the right sleeving, and does not suit a run that will be exposed to high temperatures.

Copper's weaknesses are different. It costs more as a material, it needs more skill to join well, and it can corrode in the wrong conditions. In London the main failure is pinholing, a tiny hole eaten through the wall of the pipe, often near a joint where excess flux was left inside or where the water turns sharply at speed. The question of how long do copper pipes last in a London house, what causes pinholes and when a run is worth replacing, has its own guide.

Replacing a length of copper with plastic can break the metal path that your electrical earth bonding relies on. If a section of copper near the incoming main or the boiler is swapped for plastic, have the bonding checked by an electrician.

Can you mix copper and plastic in one system?

Yes, and most houses already do. Push fit fittings accept copper and plastic interchangeably, and there are dedicated adaptors for joining the two. What matters is doing it properly: a pipe insert in every plastic end, the copper cleaned and deburred, and the joint clipped so it is not taking the weight of the pipe.

The one thing to avoid is a patchwork of repairs in different materials and fittings from different makers on a single short run. That is a sign of emergency repairs that were never finished off, and it usually leaks again. If you have had more than one leak on the same run, it is often better to renew the whole length than to add another joint.

Which lasts longer?

Both last for decades. Copper has the longer track record in British homes, and much of the copper fitted in London after lead supply pipes were replaced is still in service. Modern plastic pipe has not been in houses as long, but it does not corrode, and makers back it with long guarantees provided it is installed to their instructions.

In practice, the life of the system is set by the quality of the installation rather than the material. A copper system with clean, well made joints and a plastic system with every insert fitted will both outlive the kitchen above them. Badly made joints in either will leak early.

What we would use for your job

For a leak repair we match what is there where we can, and we tell you if the rest of the run looks like it will be next. For a new bathroom or a kitchen move we normally run plastic under the floors and copper wherever it shows, around the boiler and around the cylinder. For work on an unvented system the safety pipework is always copper.

If water is escaping now, turn it off first. Our guide on where is my stopcock shows where to find the valve in most London properties, and our burst pipe repair service covers the emergency visit. Where the water is going somewhere you cannot see, our leak detection and repair service finds it before anything is lifted.

Call 020 4652 5111 to book. Our rates are on the pricing page and are agreed before we attend.