Loft room rafter insulation

[DIYNotts]

Hello, I have a loft room which requires re-insulating at the ceiling and between the rafters. I am not sure what to put in, kinspan/isover, gypsum board, to meet building regs with the following sizes:
2.5" (65mm) rafter depth.

Could anyone point me in the right direction for a solution?

Thanks

 

[jeds]

You won't meet regs with rafters that deep. See this discussion here.

//www.diynot.com/forums/viewtopic.php?t=178038

You could build the rafters down by adding 50x50 to the underside. That would give you 115mm depth to which you could then fit 65mm Kingspan or Celotex between and 50mm beneath the rafters underboarded with 12.5mm plasterboard.

The sizes of the rafters seem very small for a converted roof. Is this a new conversion or existing?