loft insulation + breathable membrane



hi all, looking for advice on fitting loft insulation to our extension,
building control asked for a breathable membrane which we fitted.

when fitting loft insulation, the instructions say it should be fitted over the top of the cavity wall insulation, pushed right into the eaves.
if we do this with all of the 270mm insulation thickness then the insulation will touch the breather membrane at the eaves.

any advice, also have read today that some people recommend fitting plastic sheet such as dpm (visqueen) , between the plaster board and the insulation, bco hasnt asked for this what are your thoughts, seems to make sense over bathrooms. to stop condensation making way into the loft space.

also our extension has added approx 30% to the size of our property, the roof on the existing is fitted with traditional roof felt but has vents at the eaves.

would you increase the ventilation in that part of the roof or leave as is.
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