Ive had my loft boarded up so that i can use it for storage,the joiner has screwed boards on the floor and the sides,and put some hardboard on some parts of the roof,will this be ok in regards to ventilation? its an old roof ,tiles were cemented on..so is not the modern felt/tile roof.
The main thing to remember is that if joists haven't been beefed up, don't store heavy things up there (eg loads of boxes of old books etc etc). Most modern roof spaces are only designed for about 25kg/m2. Older roof spaces will generally have an even smaller capacity before the ceilings start to sag.
Personally I wouldn't have underboarded the rafters. If its an old roof there might still be enough ventilation around the rafters, but the boarding certainly won't help it. The boarding might trap any water that gets through the roof covering. If you don't go up there regularly you migh not be aware of a leak.