One of our bedrooms has apparently already been insulated on the ceiling with a layer of polystyrene before the plasterboard. As this room is much warmer than the others and the ceilings need doing anyway we are very tempted to do it in the other rooms.

I know the normal route is loft insulation, which we will do as well, but there are eves (which we have been told to leave free of insulation for ventilation) that form the sloping part of the ceiling. Plus loft access is a nightmare and there is boarding in the way as well.

If we do go for it, Any advice on material? So far we have been comparing the kingspan insulated plasterboard and just polystyrene under normal plasterboard.

We have asked 3 plasterers, all of whom basically think we are mad. Are they right or just behind the times??!!
I really need advice to steer me out of the quagmire that has developed in my brain!
Thanks in advance

Have made comments elsewhere about creating an artificial skeiling at the eaves internally (45 degrees and about 300 deep) where heat loss is greatest (creates a coffered effect in the room). The question is do you have enough height to lowere the ceiling? If you do then what about creating a vaulted ceiling? Did you know that plasterboard bends quite easily? Just lean it against a wall for a few days, if a big bend it may need a light spray with water occasionally. The beauty of a vaulted ceiling is not only that it looks good and you can put in insulation where it is needed most (well at two ends anyway) is that you can put in fibre-optic lighting and have a ceiling that looks like twinkling stars! Just batten up to u/s ex ceiling, make ply formers to the shape you want and fix more battens to lower curved edge, fix curved p/b to the u/side, stuff in rockwool/sheeps wool/ecowool as you go!

Bear in mind you need something like 130mm of PUR to meet the building regs. Can you afford to lower the ceiling that much or would it look odd? Got any down lights?

I have a similar problem, but not with skeilings. My open-plan sitting room with stairs to the side has a vaulted monopitch ceiling from standard height to about 14 feet at the peak. It's currently clad with T&G nailed to joists and the cladding has warped in places.
I suspect that the insulation between the cladding and the slates is well below current standards and I would like to do something about it. Without stripping all the t&g off (exceedingly messy), can I just add some insulation on top of the underside of the t&g (if you see what I mean)?
If so, what and how? If not, any suggestions?