We would actually need to know the support structure for these tiles before any guidance can be given. Ventilation is a requirement, but, the concerned draughts can be eliminated.

Hi
The slate tiles are nailed to 2"x1" batens fixed to comman rafters on a double roof construction.I don't know whether all these terms will be the same in the US?
Thanks very much for replying and any help would be most appreciated.

Tez

There should be no problem enclosing the attic as long as you maintain the proper clearances for ventilation.

From the bottom of the eave, up the roofline and back down to the other eave you must maintain a clearance underneath the slate of no less than 4 centimeters. This is doubly important given the damp climatic conditions that you experience. Under this, dependent on space available, you may place any type of insulation. The more dense the better protected.

On the bottom of the rafters you may place your desired material (plywood, drywall, paneling, wood, etc.).

As to the floor, you may choose to insulate between the rafters to aid in the draught elimination. Air venting is of no concern here.

If your questions have not been answered correctly, please advise.