I have the option keeping MVHR ducts above or below loft space.Trying to decide based on practicalities and headroom. How much insulation do these ducts need over/around them? There will be plenty in the loft so will be well covered but would this be enough? It would be more straightforward to keep them in a small suspended ceiling space below this but I don't want to create a particularly low ceiling and I reckon these will need minimum 150mm void to form a 90 bend?