Loft insulationI need to insulate my

Loft insulationI need to insulate my loft. The ceiling of my bedrooms is made of chestnut wood planks. This is also the floor of the lost space. I am thinking of using a foil backed solid insulation such as kingspan and laying this directly onto the boards. My one concern is could this trap moisture ? Any one out there used this or have any other suggestions? Many Thanks