Insulated plasterboards - are thinner ones worth installing?

moneysaver1978

The reason why this thread piqued my interest - our new house is a 1930s semi solid-wall with an EPC D and 100mm loft insulation so we need to add additional insulation on top of the existing 100mm. The space between the joists are 40cm.

Option A was my original plan:



This option means, I require around 140 loft legs or something like that (each requiring 8 screws) and I would no longer be able to stand up in the middle. Thinking now if boarding the full width of the roof is really necessary which brings me to Option B:



Although Option B still has the issue of reduced height, it does require a lot less number of loft legs and perhaps the existing chipboards are enough so a good MSE! But now... thanks to this thread, I wonder if mixing PIR and roll insulation (Option C) would give us the best of both worlds.



While Option C is more costly than Option B (I need to do some maths later!), there is no issue with a reduced height, no need to purchase loft legs or chipboards.

https://www.insulationsuperstore.co.uk/product/warmline-insulated-decking-board-2400mm-x-1200mm-x-156mm.html

Or is Option C unworkable and won't improve EPC?