I am planning to replace some tatty loft insulation and then lay loft boards (Wickes) over the joists, to provide a cleaner storage area. The Wickes project guide recommends either using a total 270mm depth of insulation roll in the joist gaps, or (ideally) filling the gaps between joists with 100mm and then cross-laying 170mm at a right angle over the joists. Because my joists are less than 270mm deep, either method would mean my loft boards will sit directly on the insulation. I gather from posts on this forum that this will cause 2 issues: 1. Squeezing air out of the insulation - makes it less effective. 2. Removing opportunity for air to flow over the insulation roll surface - causes condensation. Any advice on how I should proceed?