pipes in underscreed insulation

[Tim Lamb]

Next extension issue...

The plastering is now complete. Laying in 100mm of floor insulation and then the Polypipe underfloor heating is next.

At some stage pipe runs to the shower room need installing. The builder has already hinted that he does not consider separate cold water

*non-softened* feeds to the toilet necessary so I am hoping to be armed with good advice regarding laying in.

I assume the pipe used will be plastic.

Are under-screed T's OK?

What sort of hot/cold segregation is advised?

Local isolating valves above skirting obviously but how do you get from push-fit plastic to compression/solder copper? Do you go straight to the flexi tap connectors?

What is the preferred way to supply a shower? Tray type and cavity wall hard plastered.

Are there issues with using combi-boilers and mixer showers?

regards

[The Natural Philosopher]

Possible but not mandatory.

Not really, strictly.

Run all pipes whether copper or plastic in insulating foam sleeves sleeves.

You can push fit onto copper. Personally I would lay all copper, with insulating sleeves to allow for insulation and expansion.

? Pipes seem to work for me?

Not really.

[Roger Mills]

I'm not sure about the legality of push-fit fittings buried in screed - but I certainly wouldn't fancy it. If using plastic pipes, I'd use continuous runs - and only fit fittings in 'fresh air' where the pipes emerge from the screed and run up the wall. If using copper pipe, soldered fittings under the screed would probably be ok.

Not *all* pipes - I wouldn't recommend that for under-floor heating!

[Andrew Gabriel]

Where plastic pipes run through concrete/screed, make sure they are pressurized whilst it's setting, if possible.

Plumber won't mind, but he doesn't have to live there. I'd prefer no joins in such inaccessible places.

ISTR there's something in the building regs, to make sure hot pipework doesn't heat up cold pipework. (Never seen any plumber even consider the issue though.)

You can use compression fittings on plastic pipe, but make sure you use pipe inserts or it will leak. (From my limited experience with plastic, I'd also say use metal pipe inserts and not plastic ones. Plastic ones have to be larger, and probably restrict the flow more.)

You could do. The problem with having plastic pipework visible is that it will never be straight runs because it will curl. If it's hidden from view, this doesn't matter.

I chased the pipework into the wall (but it was a 9" brick wall). I sleaved the 15mm copper with 20mm electrical plastic conduit under the plaster. (This would probably work with 15mm plastic too.)

Yes. You should have a thermostatic mixer valve that's designed for multipoint and combi boiler use (high cold pressure, widely varying hot pressure). Cheap mixers don't work so well, because they aren't fast enough response to changes in hot pressure or temperature, and they don't realise they can't change the temperature of the shower outlet by changing the hot flow rate.

[Simon]

I put in a hot/cold pressure balancing valve before my thermostatic mixer which is supplied by combi, and the result is very satisfactory. Not sure if the mixer (triton tyne bar-style) would have been OK without it though. I believe some expensive shower mixer include both functions. Arguably a balancing valve and basic non-thermostatic mixer would work, but its nice to know the temperature is repeatable day to day. Simon.

[Tim Lamb]

In message , Tim Lamb writes

Right.

Summarising the response...

Avoid under screed joins in plastic.

Plumb in copper above floor level to achieve straight runs.

Segregate hot and cold using insulated sleeve.

Exercise caution when selecting shower mixer with regard to varying hot supply temperatures and pressure.

Shower plumbing can be buried in the wall.

Easy:-)

But, how do I fend off a builder who may want to slap 100mm slabs of Celotex on top of a couple of plastic pipe runs laid across the oversite?

regards