insulate a ceiling

[stevie-b]

Hi people hope your all well, I am in a right pickle and could do with some ideas
i am wanting to insulate a ceiling in an old cottage. The existing ceiling is lath and plaster directly on to the joists then there are the slate tiles. a total distance of 100 mm max and no where to put insulation.
the area is a crock loft so it currently has a maximum height in the apex of the roof of 6 foot.

i have two purlins that are 150mm into the room and i think i could reduce the ceiling height by no more than 50-100mm.

what is the most effective way of insulating the house bearing in mind the need for limmited thickness?

 

[Deltamale]

If the existing lath and plaster is sound (no cracks or loose areas) you could apply Gyproc thermaline, see http://www.british-gypsum.com/products/gyproc-thermaline-plus in thicknesses up to 90mm which includes the plasterboard finish and need only to be screwed in place and can be wet finished or dry line finished and sealed.