Sealing ends of joists for loft boarding

[hyposmurf69]

Hi I'm currently adding loft insulation up to 300mm and part of the loft near the loft hatch in going to board up for loft access and possible bly done storage.I have since 4x2s and tongue and groove boards.Im going to run the new 4x2s perpendicular to the current joists and then possibly another set perpendicular to that.I have a reduced head height in my loft so maybe need to just board to a certain height and then add some I insulation on top that can easily be removed for access to water tanks and rest of loft
By running the joists perpendicularly to each other this will create open gaps at the ends.Should these be sealed with smaller sections of joists or is it good practise to leave the sides open so that moisture can be released that rises from rooms below?Ive also heard if leaving a gap above the top layer of insulation and the boards to prevent damp.

Where do building regs stand on sealing in the sides of the joists would the be more in favour of sealed or open for ventilation?

 

[Murdochcat]

Lofts must have, in the majority of homes airflow

 

[hyposmurf69]

Hi I realise they need air flow running up from the soffit vents and through the loft but do I need to keep the ends if the joists open as well.im talking about an area like a an island within the centre if the loft so not any where near the soffit vents.The sides to the outer perimeter of this island and the sides of the inner perimeter to the loft hatch.