Onoff

Dry?

Your doing?

The one @Nickfromwales said above, I imagine you could ditch the oil filled rad then.

I'd fit a single room MVHR unit. Fresh air and heat recovery. Around 75% efficient.

Please! It's TREKKERS!

Just read 35mm one end not 30mm! I have some foam backing rod here, could send you some.

You can grey foam first - you would still have too cut it to an oversized taper, then BT1 the whole width, from 0 to 30mm. Someone good with silicone could do it. I wouldn't try without a Fugi Cramer silicone tooling kit. The foam is primarily there to stop the silicone falling through. Or put the grey foam in as above then bed the plastic trim on top. The foam stops the plastic trim sagging whilst it sets.

Think my bathroom was 70mm out on two opposing walls.

You could counter batten at this point. First foil tape all the joists and PIR joints. Make sure the wires coming through are sealed. Counter batten deep enough to suit low profile downlights then plasterboard. It's what I should have done.

I have to do some "reinstatement". I've compromised my vcl in so many places: The fire hood will be stuck down where it's rim meets the foil/vcl: Edge of foil and vcl: With hindsight I'd have done a suspended ceiling!

Did none of you save those Bazooka Joe wrappers as kids?

30mm is a massive width to fill. You really need backer rod or something.

You could fill with foam backer rod - cut to fit. Tbh you can use cut down pipe insulation. Then I'd over seal with white BT1 not CT1. White CT1 will go yellow over time. Cut down insulation used as backer rod. Alternatively do you have any uPVC window board etc left over? Cut and stick on again with BT1. https://www.toolstation.com/bt1-ultimate-bathroom-adhesive-sealant/p74523?

As with airtightness, the Devil is in the detail!

Over Sexed Bristolian.

I assume you mean on the inside? That second Illbrück video I link above shows taping the window to the frame. Starts about half way through. As for foam then the Illbrück FM330 stuff stands head and shoulders against all the other foams out there imho. "hardly anything for the compriband to stick to" It really doesn't need much of an unsealed gap to lose heat / get a draught through.

For example. The tape I'm on about, colloquially called "compriband", whatever the make, expands massively to fill the gap. You can get it adhesive one side that you stick to the window frame JUST before it goes in. Or tape you push in afterwards.

Some of the black washers are formed conical.

That's an access/rodding point for cleaning the trap out. Try turning the rubber washer around. You need to be 100% sure it's not leaking from higher up and running down to there.

I agree but Jet Blue isn't a sealant per se but a joint compound.

Where the white meets the black? Going to be a bitch to get any PTFE tape around there for instance. In the white bit there should I think be a black rubber O ring and a solid backing washer? The backing washer compresses the rubber. Think I'd try and smear the threads with say Jet Blue Plus.

It's really not hard to get a seal there if the right product was used. The expanding tapes are great for this sort of thing. Expensive and you need your wits about you to use them. Sadly the average bodging builder will resort to foam, cheap foam at that and often after the event. Would it pay in the long run to have the windows removed and refitted?

Understood. Sadly all these little areas basically add up to one damn great hole in the airtight fabric was how someone here put it the other day. A great if sobering analogy.

Surely the windows were sealed around? Are you meaning there's no Compriband/foam between window frame and structure or no airtight tape inside?

Do you have any details / pictures of the area where you had to compromise? Reading above it sounds like where the ends of the joists abut the wall there's a continuous missing airtight layer? That is a horrible problem to have. I think though someone on here did address similar, taping around the ends of every joist and possibly using an airtight paint. I'll try and dig the thread up. It sounds like a poor design unfortunately.