Lead roofing tends to get recycled into bullets in time of war, but those roofs that don't, are typically there forever (400+ years) and never leak. Some plastics are UV resistant due to additives but even copper struggles to compete with lead as a roofing material. You only need to look back to the 1970s to find PEX water piping and the disaster/flooding it can cause due to age.

Are you thinking of polybutylene pipe, rather than Pex (cross-linked polyethylene)?

> Lead roofing tends to get recycled into bullets in time of war

That's interesting - I've read that there are a lot of castles and stately houses whose demise started from the owners selling off the lead roof, but I never understood why it would be so valuable that you'd destroy the building for it. Is that why?

Quite a number of British monastic churches and castles had their roofs sold off by Henry VIII, who was fully intending to destroy the building.

Using McMaster-Carr as a benchmark, lead sheet is a bit more expensive than the same size and thickness of 316 stainless sheet. One of these is extremely toxic and the other is pretty much harmless. (Also, 316 stainless won’t magically corrode if there’s condensation on it, and the Internet suggests this is a problem with lead.)

Sure, lead can be molded into place with traditional techniques if you can find a competent roofer with a sufficiently minimal desire for self-preservation. But modern standing seam roofs work pretty well.

Hopefully you don't have a fire....See: Notre Dame

Those don’t seem like comparables though. Lead is just one (or arguably a handful of) compounds, while there are at least dozens of species of plastic.

I highly doubt it. They don't seem to be perfect, but they clearly aren't anywhere near as toxic as lead.

Plastics for potable water tend to be copper lined where I live, not sure what is used elsewhere.

I've never heard of copper-lined PEX, can you tell me more?

I think op may be referring to 'barrier pipe', which is a plastic -copper-plastic sandwich, which is designed to keep out pollutants which can diffuse through the plastic - eg. Diesel oil.

If you don't use it for underground water pipes in cities, you'll normally get complaints from homeowners about 'chemical smelling' water, particularly first thing in the morning when water has been sitting stationary in pipes all night.

oh dear i forgot that plastics are permeable to petrochemicals lile paper is to water

There is a test for plastics where they weigh a block of plastic then soak it in water and weigh it again. For some plastics the gain in weight can be a few percent.

That's like saying "metal is strong". There are huge differences among different plastics.

Well, there are < 100 metals but thousands of varieties of plastic?

Not thousands, certainly not in common use. But yes there are many, and they have very different properties from one another, including permeability.

Barrier PEX (often referred to as PEX-Al-PEX) uses a layer of aluminum, not copper. A far more common type of barrier PEX uses a low-permeability polymer coating.

Oooooohhhh.. That make sense. Today I learned.

I still have a length of it in storage but I don't know the brand by heart. It was pretty expensive stuff and it needed weird fittings, which were also expensive, the inner liner was blue, that much I do recall. In the end I mostly regretted going for plastic, I'd probably use regular copper pipe and crimp fittings again, less hassle and I'm just more familiar with it.

Do you mean PEX-Al-PEX? It’s mostly obsolete now, in favor of “oxygen barrier” PEX. The latter is generally approved for potable use, but there’s no reason to use it. It’s intended for closed-loop heating or cooling systems that contain non-stainless iron alloys, and the idea is that any oxygen initially in the water will be rapidly depleted, and deoxygenated water is not corrosive.

Probably alupex "meerlagenbuis"? Comparing it to copper it seems to be much more affordable per meter. I worked mostly with copper in the past, but did some work with alupex on my brother's house a couple of years ago. It's much more convenient and affordable than copper!