I have a loft conversion I intend to re insulate.

Im thinking of removing the plasterboard to the pitched roof and using
50mm Kingspan or similar between the trusses leaving a air space between
the tiles for ventilation. Then possibly battening by 25mm and using the
thermofoil type material now available, such as

http://www.wickes.co.uk/Wickes-Therm...mmx8m/p/210022

Or I could use a further layer of 25mm Kingspan with no battens then the
plasterboards.

Any thoughts?