Iceverge

The timber intel over the door looks to stop about 150mm over the pillar. That would need to be propped removed and extended before hacking the pillar done. More pics the better. Show outside too.

https://www.gumtree.com/p/plant-tractors/hitachi-digger/1499766158

Sweet spot is where they leak oil slower than you can pour it in…. Get organised, hire somebody with a 13t and dumper or heavier to get everything roughly in the right place. Then do a few days hire yourself of a 3 tonner for the fine tuning. Or else buy the very best you can afford, it’s frustrating moving soil with a digger though. Wrong machine for the job.

Could you perhaps label the materials in the drawing please and also draw the neighbours conservatory and pipes. In my experience nothing deals with water long term better than gravity. This would always be my first port of call. Establishing a low drainage plane for any liquid to flow harmlessly away. Failing that mass concrete is an option. I'd be tempted to pour a 200mm reinforced retaining wall at the boundary line of your property and forget all about the neighbours pipes. Maybe something like ICF could actual work with the concrete core acting as the support for the outer leaf of your extension.

Nope! Just get it in a position that you won't need to move it for a stroke.

I wouldn't worry about it.

Eps is a great material in the right application (usually underground !) but you've hit the nail on the head with fire concerns. It tends to melt into air the small bit of liquid dribbles away then when you burn it. Alarmingly quickly too. Rockwool hardrock is expensive in comparison but over your area the difference won't be mega. I'd stick with that. There's other brands too. Knauf rocksilk etc or maybe woodfiber. Is there any reason you don't want to have fullfill rafters with insulation inside like I suggested above.

Yup they're rubbish, specifically sliding sash with brush seals. You can get fake ones with the horns that look ok but I'd be looking at compression seals on the windows whatever I did. Have you considered that noise may be coming through the ceiling or from under a suspended floor too?

Might you have forgotten that you put kooltherm in there instead of PIR.......🥷. Say 50mm between the rafters and 80mm below....... Also stupid rules. This would be easy to solve if everyone was allowed to simply bulldoze and rebuild their houses properly every 70 years.

Top down, Tiles 38mm Tile Battens across the rafters 25*75 Battens up the rafters Glidevale VP400 membrane. 11mm OSB taped at all joints. 200*44mm rafters at 600cc full fill with blown cellulose ( or mineral wool batts) Airtight membrane, 45*50mm battens at 400cc across the rafters with 50mm mineral wool in the service cavity . 12.5mm plasterboard a skim. U value about 0.17.

I would argue this is exactly what you need to avoid, primarily through good airtighess. Buildings die when water (in whatever medium ) gets into the structure and cannot get out. Stop all drafts taking vapour through a structure. Also at all costs avoid sandwiching materials of very low permeability. That's why I don't like the polythene VCL, Foil faced PIR and EDPM all together. If water gets in then it's never getting out. Always better to stick to one impermeable layer maximum. Are you suggesting that just having poor airtightness is a solution to ventilation? That's much the same as having a hole in the roof as a solution to getting drinking water into your house. Beware your designer and NHBC aren't gospel either. It's a woefully misunderstood topic this. Stick up a section of your roof and we'll have a look at it. What roof covering is on your current house?

Reality unfortunately gets in the way of these assumptions. Mistakes and sloppyness are a part of building and I think any design should be somewhat tolerant of non perfect workmanship.

It's there in pretty much every detail. That comes up on Google so I assume that's how the majority are built too. Ply or OSB above the insulation. I think you can get some types of insulation with specific fleeces bonded to one side to take grp/EDPM.

Also I would prefer something like metal cladding as instead of EDPM or GRP as it isn't weather dependent for install and as vulnerable to imperfect workmanship.

I think we're storing a mountain of problems with unventilated flat roofs in the long term. The grp/edpm is the only barrier to water ingress. Its waterproofness is completely reliant on its total integrity. Being exposed to the temperature variations of the sun and weather it will inevitably fail at some stage. The first thing the occupants will know, is water will emerge from somewhere in their roof, with zero clue to where it started. Maybe months after it has failed, in the meantime causing significant damage. We all know how sloppy builders can be with membranes so I bet most VCLs are full of holes or nobody's taped the joints properly. The layer of OSB under the is GRP is the ultimate stopping point for the internal vapour to condensate. I think these will start to rot out and nobody will know until the roof leaks. I would far prefer something like this. GRP/EDPM 18mm OSB 25*75mm battens across the joists. 25*75mm battens up the joist with the void fully ventilated at both ends. Breather membrane Rigid insulation. Furring strips. 18mm OSB diligently taped as airtightness. Joists . Plasterboard I would also happily install insulation between the joists if I was doing it myself for a hybrid roof. However I understand the issues and am picky about details.