Onoff

Rip it out and start again. Clean all the silicone off of it, every last bit. Was the trap the same make as the tray? Sometimes the trap rubber washers are generic thus a bit of a crap fit to that particular tray ( so said your uncle way back). I can only go by what I did and the tips given. I ditched one washer and loaded with Sika EBT. The top side has come out really well IMO. I wasn't overly fussed about underneath. Baby wipe around and walk away until set: Did the same with the overflow:

@Construction Channel I seem to recall did his own, DIY underpinning, in stages.

1860's? ?

You've got wood?

Each to their own but you listen to some weird, off the wall stuff!

I used white SikaFlex EBT on my bath waste and binned the washers it came with.

Got his name written all over it. Quite a few sores visible in that picture...

I think I've seen this sprayed on a wall.

ST collector:

Sorry, didn't read 'outside", saw the black bits inside I thought were the dreaded black mould.

Could you have built it turned through 45 degrees and had a condensate drain?

Not here. I've got the biggest Band A Yagi available as at the bottom of a valley. A fringe area and then some.

In all seriousness it'd be nice to down tools and chill on the sofa during a break from the office side completely. Pity you haven't a floor to ceiling window you could put the sofa in front of.

The Bristolian school of Pocsterism dictates one's computer monitor should not be visible to anyone entering the room.

Get some nice cheap, sloppy Slik door gear. It's the AK47 of the pocket door world, it just works!

Like Nigella?

Do you mean aliens?

Don't forget reflexologists!

Haven't you already got a DPM under the slab / DPM at the base of the blocks where they sit on the slab? If so, and the blocks are being clad externally, I can't see the issue of how they will get damp hence maybe leave as is.

The 5mm gap is the gap to aid fitting. It MUST be filled otherwise it's just a route for the outside cold. The expanding foam has enough "give". You will need a proper foam gun and low expansion foam, gun cleaner etc. I'd also run some masking tape up the window before you do it. The absolute ideal, professional method is to use an expanding foam tape like Coompriband before the window goes in. Around the outside of the window and cill is a channel. You stick this tape on only when you know the window fits and you have to be quick about it. The tape then expands from say 5mm thick to 25mm thick and seals between window and wall. Those in the know here actually go to the lengths of, in effect, applying airtight tape around their windows to where they meet the walls. It's all very well btw, sealing everything up but you must consider ventilation to. Have your windows got trickle vents fitted?

Were there wooden windows there before, that the uPVC windows replaced? Have you got cavity walls? Two brick / block skins separated by a cavity. The ideal when fitting a replacement window is a 5mm gap all round but perhaps had to achieve in practice unless you DIY, chip bits of wall out to measure the old wooden frame exactly etc. A firm you get in won't go to the nth degree and likely allow a bit more. Or as you and I know a LOT more to make fitting easier. They won't give a sh!t you're left with draughty gaps forever. The ones that did some of my windows didn't even use foam. Tbh I'm not sure what I'm looking at there ref that black DPC. Yes, that's what it is, judging by the diamond pattern in it. Comes in rolls 100 - 200mm or more wide. Traditionally, wooden frame windows would be wrapped in a damp proof membrane to stop the frames getting damp and transferring damp/cold, from the outer to inner wall leaf (assuming a cavity). Is it wrapped around the uPVC frames and just tucked over inside? I've seen folk wrap a uPVC i.e "plastic" window in more plastic before, insisting it "stops damp" ? @craig is our resident window expert and can probably best advise what you might have there and the history of fitting.

Acoustic tiles? I used to line the WC reveal and deaden the flush / fill noise: Or egg boxes... ?

It was a thinly veiled jibe ref your prowess with the stuff! ? Seriously though, isn't the humidistat just doing its job? I reckon if I got the UFH going it'd help dry the wet room floor out and the fan wouldn't have to work so hard.

Maybe there's leak on a solvent welded joint?