Redbeard

Hi @francis0990, I don't think there's any substitute for structural engineering advice, whether from an independent SE or from the timber frame co.'s SE. As @markc states the doubling suggests load-bearing, and it is not worth taking risks.

Some installers will say a 'thin solution' ('insulated mat' - type pipe trays) is OK. I am very convinced it is not. You don't want to be heating a void or a slab. A client had 75mm PIR below UFH and I still do not think this is sufficient. I would like to see 150mm. (BTW, it does not have to be PIR - other choices - including natural materials such as wood fibre or cork - exist).

You say "the most i feel I can sacrifice in height is 5mm including wood floor." but then you go on to say "What would be the best to put as underlay? 25mm eps topped with backer board". 25mm + backer board is a lot more than 5mm! Was the '5mm' figure meant to be '50mm'? If the latter then a vestigial flooating floor of 25 PIR, DPM as VCL, 18mm T & G OSB + finished floor may 'cut the mustard'. Not goood enough for UFH, though, IMO. Remember, though, if you lift the ground floor by c50mm you put your stairs out of compliance with Bldg Regs, unless you can make the bottom stair a 'landing', in which case, IIRC, it can have a lesser riser.

The problem with using a long extension tube is that it slows the flow very significantly, so the tendency (on full pressure) to blow in and 'stick' is lost, and you get a lot of falling back out. Could you not open out more on the outside, weasel a bit of board over the hole on the inside, then fill back towards the outside before finishing with brick or whatever the external skin is? As far as the drain connection goes I wonder (if you could let off the bracket on the horizontal run) whether you could get a 110mm stop-end, drill a hole in it and shorten the 'pipe end' so that you can slot it up onto the 40mm waste, then down into the rubber of the socket end. Then a finger-full of silicone to seal, if you feel the need to seal.

I doubt there is a difference between a hole in the sash and a hole in the top rail, but the top rail appears to have mmore 'meat' - unless there is a bigger 'downstand' on the outside). Why would you want to fit a trickle vent into a tight space on the sash instaed of a more generous space on the top rail of the main frame? @HughF asks an understandable Q, but one answer could be 'as part of a thought-out decentralised mechanical extract (dMEV) system' (if MVHR is beyond the pale).

Don't know what the claimed U value is, but my rough 'n' dirty calc (assuming 2 skins of brick, where yours will be 1 x brick and 1 x block) doesn't even get the Bldg Regs (England) U value of 0.18. It might if you substitute lightweight block (and maybe, as often happens, if you assume that the air gap has still air in it - which it almost certainly won't!) but it'll be a close thing. Also the 'spec' is incomplete. 50 PIR inside the block skin is fine, but what is it finished in? If it's insulation-backed plasterboard then (a) it is 50 + 12.5mm and (b) the VCL will only be perfect on the back of the boards. The joints won't have one. If worried re loads on the wall you could do 50 PIR, taped tightly at all joints and perimeters, or add a plastic VCL treated similarly, screw 25mm ply to the wall and then plasterboard (or even Fermacell if you don't dislike cutting it as much as I do). It's a faff, though. If it were me I'd consider getting the cavities built empty (and I'd be tempted to go 150 - 100 is not too exciting - and carefully (no rubble and cr*p inside) then get the cavities fully filled with graphite EPS beads when you get your old cavities filled.

Welcome! You don't mention insulation, but I guess it is 'fairly original' but with 'non-original' roof insulation and the addition of cavity wall insulation. What's the insulation spec?

I confess I did not always dampen down, , and I never had the 'expansion failure' that you have had. Have you asked SF to investigate? I am sure they will refund, but it wants more than that, I think.

Used mountains of No Nonsense foam and never had an issue like this. A few stuck valves, yes... I have now moved onto (much more expensive) Illbruck FM330* and would not use anything else (unless I want adhesive grade, of course). (*Satisfied customer - not salesman!)

"It is almost completely air tight but at the small points where it is not...." Errrr....... Good luck with the 'negotiations'. Of course they may not entertain comparison with others' products but what your pics show is not typical.

Yes, that's not right. The fact that you have condensation on some of the frame and not on the rest suggests a local shortcoming. As far as the condensation on the glazing goes I don't know the glazing spec but my triple-glazed (3G) windows (some 4/18/4/18/4/soft-coat Low E/Argon and some same spec but 16mm and 20mm spacers respectively) have *never* had any internal condensation*. What's the make-up of the Velux 3G unit? * Loads (frozen) on the outside!!

200 PIR will give you 0.11 at worst. What is your target U value and how much extra will the M-F give you? If the timber counter-batten is 25mm I would wonder about loading it up with the wight of the 'sandwich'. Are you going to use stainless screws to reduce thermal bridging? Even if the battens are only 25mm how much will x number of minimum 250mm S/S screws cost?

I wonder if the ridge section is the width of a 'landscape' panel, in which case I guess you'd get 5 panels up to the L of the stack. One more can go anywhere you want in the remaining triangle. I think 9 might look 'busy'. I am no expert of aesthetics, and not a lot bothers me, but I think the 'notchy' look where PV 'climbs a hip' is not to everyone's taste. Prices look about what I'd expect. Some have, I think, had 4kW for £4k or just under, but £4400 sounds acceptable to me (especially when that could have cost £17 - 20k in 2009/10!!

"...So I’m not looking to fit solar panels " Presumably not = 'now'.

@Temp writes: "The void under the membrane can also be reduced to 25mm just to allow the membrane to drape correctly". This is the 'rule' used by many membrane companies and by most roofers retrofitting insulation over a room-in -the-roof, and what I have used for many attic bedroom retrofits, but the most recent government guidance (https://www.gov.uk/government/publications/room-in-roof-insulation-riri-best-practice) suggests 50mm if I remember rightly.

If the ridge height is really a problem could you have a mainly-vaulted ceiling with just a tiny dropped area at the apex to allow an air-passage/'plenum chamber'?

Eaves-to-eaves ventilation works for a huge number of roofs, but it may not work for your BCO... My house has no ridge ventiulation and no moisture issues (well, not in the roof....)

"I’d compare ChapGPT to a very recent joiner at an accounting firm". Ah well, that's where they're going wrong! They need an accountant.

As @ProDavesaid, try ringing from a number he will not recognise. If he puts the phone down when he realises it's you then you have a pretty good idea of where the land lies, but it *may* be that you have time to explain that you want to resolve this in a way that works for both of you. Worth a try...

It was a little less straightforward for us since (a) every extension had to be birdsmouthed and (b) the roof has spread in the middle. At that point I was glad I wasn't doing that bit. Less glad when I got the roofer's bill! We had to extend eaves x 1 elev and verge x 1 elev (we only EWI'd 2 sides). We bolted rather than nailed.

If you want it to be useable I would bump up the 40mm PIR straight away and yes, insulate your floor. If you are looking for quick warm-up, however, you may be better with a floating floor on top of the slab rather than insulating the slab.

An external pic with context would be good - for my part so that I can see whether external wall insulation (EWI) might be an option. You say "the roof definitely needs changing, but again is this something that would require completely starting from scratch? Would an experienced builder recommend a new flat roof or a pitched roof?". Again, pics will help, and heights (from surrounding ground to current top of roof) so that we can look at it in relation to Permitted Development (Planning) rules.

@Mr Punter, as I read it I think that when @richo106 says 'over the top' it means 'underneath', as the next things are VCL and plasterboard. @richo106, can you confirm?

Agree with @ProDave. You *might* find a manufacturer's tech dept might suggest a lay-up, but I should have thought they would fight shy of 'designing', in terms of the potential liability.

That's not what I'd call a Warm Roof, whatever the caption says! A 'full' Warm Roof has all the insulation above the rafters. A 'hybrid' WR has some above and some between, but beware of interstitial condensation risk.