As a designer of loft conversions from a structural engineering point of view, i certainly agree with the previous comment from Mike H that you should never remove any timber from the roof or ceiling structure without professional engineering advice. As for insulation, you should always leave 50mm or 2 inches of ventilation from the underside of the felt and also add slate/tile vents near the apex if you don't want the build up of moisture. This means that in most cases you cannot place more than 25-45mm of insulation between the rafters. As for fixing plasterboard to the underside of the rafters, you should consider that most roof structures in houses over 50 years old are not capable of passing modern Building Regulation loading, so adding extra load will increase the existing deflections. It will however be unlikely that the addition of plasterboard will over stress the structure, causing failure of the timbers. Without wanting to sound to pessimistic the most important thing you should install in your loft is a linked fire alarm. In a two storey house it is unlikely that you will hear a smoke alarm ringing at ground floor level when you are running locos in the loft. By the time smoke reaches you your exit may well be cut off. On a more positive note, roof voids designed under Building Regulation approval in the last 40 years have ceilings capable of carrying the most ambitious layouts. So happy constructing to all!!!
regards
Dave
regards
Dave
