Looking at having an extra bathroom put in. It will be on the 2nd floor/attic. We currently have a sink up there and the water pressure looks good enough both hot and cold in my unqualified opinion. We have a combi boiler. I’m concerned that if someone is using the shower downstairs then it might not be so good.

Would you recommend running it off the combi hot supply or just putting in an electric shower off the cold supply. We’ll have a sink so there will be hot water going up anyway.

Is there a “norm” for this type of thing? Anyone got experience?

If you’ve already got hot and cold up there I’d use that, for an electric shower you’d have to run a 10mm(I think) cable directly from your consumer unit to the shower, causing big disruption to you home not to mention the cost.
Money might be better spent on a more powerfull combi( you don’t say how old it is).

I think it depends on the rating of your boiler – how much water (flow rate) it can heat.
That’s where I’d start anyway.

causing big disruption to you home not to mention the cost.

About £1/metre and a few hours work with a chaser and then polyfilla…

Depending on your water pressure, running a cold feed might not work anyway – if more than one person is having a shower it could still be effected, just in a different way.

Is there a “norm” for this type of thing?

I think the norm is to shout, very loudly, ‘Hey! Y’Dads havin’ a shower, don’t be buggerin’ about wit t’water or you’ll feel t’back o’miyand’.

Might have a play later and see what happens with the pressure when I turn various things on. I’ll check the boiler too. It isn’t that old…

Cold pressure is very good but it will drop when one shower is on anyway. Thermostat taps will stop people getting scalded.

Not too worried about the electrics side as we are doing other work and planning to decorate the hall anyway.

Do sparks still run cables down wall cavities? Of course, your house may be too old, etc…

Even with a giant 42kw Worcester, you won’t be able to run 2 showers at the same time if that’s what you’re thinking.to do that you need an unvented setup