boarding over insulation

[bazil-brush]

I wish to board out my attic but i have concerns that i will compress the insulation tightly between rafters and this will not allow the timbers to breath. Am i going to get problems with dry rot etc?

[Deluks]

Rafters are above your head and support the tiles/slates etc.

or do you mean joists? ie: upstairs ceiling/loft 'floor'

If it's rafters then you definitely need an air gap (minimum of 50mm between insulation and felt/tiles), otherwise condensation will form where the warm air inside the roof meets the cold air outside.

Between the joists, not such a problem, although never insulate right up to the external wall, leave a small gap round the edges.