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I’m refurbishing a early 1930s property. Detached. Solid brick wall construction with crittle windows. Im part way through, structural demolition work complete, 1st fix plumbing done. Electrics 1st fix yet to start. The putting back together has started as the builder has started putting ceilings back together then he will halt till electrician done their work. I wish I’d found this forum sooner!!!! So many questions and queries I’ve had along the way. Ive got a question about insulation but hopefully will be able to post on that forum soon specifically but in the interim here is my query: I am having brand new ceilings put in ground floor hallway and 1st floor bedroom. Above is loft. It’s a solid wall property with no wall or floor insulation. Ie high heat loss. Double glazed windows are ordered. I want to specify insulated plasterboard for new ceilings for thermal performance (not acoustic). My builder has said most people either just use standard non-insulated plasterboard and then rockwool on top in between the joists. He thinks I’m going overboard. My builders alternate suggestion was a standard plasterboard with 1cm foam, (which I think is called a PUR board?) and again rockwool In between joists on top. Is this effective? I was thinking PIR board. But then what brand and thickness is appropriate?? I just need advice on the most effective material/method for insulating ceilings in intermediate rooms? Ie bedtooms/lounges from a thermal perspective. I rang buildbase: They said they have 6 different products. 1) Siniat PIR board at 37.5ml - this is what they recommended as the most effective. 2) Thermal XP board 27ml 3) 4 different thicknesses of polystyrene (foam) plasterboard at 22, 30, 40 and 50 ml. My builder suggests getting this last one at 22ml and that with rockwool in between the joists too will suffice. He is a youngish builder, early 30s whose forte was the structural work and how I originally appointed him. He’s great to work with, but there are are areas sometimes where I wonder if he’s out his depth or experience. He does listen to my concerns and is willing to work with me But I would really appreciate guidance on appropriate product. Like I said earlier, he said his previous clients all just used non-insulated standard plasterboard and rockwool between joists at ceilings at ground and 1st floor. My my concern is this is an old property, very poor thermal performance, i just want to do what’s right for the property. Im not sure if I’m going overboard or overworrying. Detached property. The windows I have upgraded from single to double glazed. Wall insulation - external I couldn’t afford!!! Internal I don’t want to lose floor space. Floor is suspended timber non-insulated. Roof insulation I will do and board up as plan to use loft for storage. Ceilings wise - whilst putting up new ones if too far gone during structural work, I want to do right/effective thing thermal wise. Any insight from those in the know would be appreciated property is in london. Building regulations don’t apply as refurbishment of existing property (no extensions). Photo attached of plasterboard builder suggests 22ml siniat PUR board https://www.siniat.co.uk/en/products-and-systems/products/internal-boards/gtec-eps-thermal-board this is product. Is it right one??? many thanks

A while ago I remember seeing some great photos someone had posted showing their ceiling insulation between web joists prior to boarding. I am just about to start this job & seeing the photos again would be so helpful. I have tried to find with lots of searches but to no avail. Anyone remember this? Thanks