Hi guys, new to the forum as a poster although I have gleaned much good advice from the forum in the past. Been wondering for a while why my lounge (17m2) is always so cold, even with the 10000btu rad on full tilt it never really warms up sufficiently. Obviously this can only mean poor insulation. The lounge is in a flat roof extension which was built in the 80's it was signed off by building control but it seems back then they were a lot less strict. I knew the flat roof was insulated but I though I better take a proper look, it seems that there is about 100mm of mineral wool insulation fixed to the bottom of the deck with a 50mm approx. air gap between it and the plasterboard ceiling. As if that wasn't bad enough a few years back the previous owners had all the sofits and fascias replaced and they have fitted mesh vents in it. So now I have a 50mm air gap between the ceiling and the insulation and cold air circulating through it, no wonder it feels like the door is open most of the time. What I want to know is do I need the ventilation since the insulation is fitted to the underside of the deck? The rooms below have recently been replastered and the felt was replaced in the last 5 years so I don't really want to be ripping either the ceiling or the deck off.