Can a loft have both ceiling and roof insulation?

like the rest of the house it will need ventilatyon & heat if you want to avoid a build up of condensation creating dampness what you are trying to do is create a loft room on the cheap without the proper building control regulations, lofts are meant to be cold draughty places to allow air flow to the timbers to stop them rotting , unfortunally people want to live in a lttle sealed bubles your house needs ventilation to prevent condensation creating rot & dampness

You will normally find that building control ant to see a fire proof insulation under the loft floor. As part of the work its standard practice to roof the property using a breathable membrane under the roofing lath, venting the insulation. If you don't reroof you'll need to install some vent tiles into the roof. All your doors on the stairwells will need to be upgraded to fire doors too

I do agree with the previous answer. However, so long as you leave a void above the insulation in both cases, then it allows air to flow but in the case of the floor, your soffits will have to be vented to allow air. With the ceiling, if you use a breathable membrane then that will allow air flow. Hope this helps Liam