Insulating Roof

[HopelessatDIY]

I live in a top floor flat and in the bedroom the roof has zero insulation.
I have roof tiles and below that roofing felt/paper. Attached to the underside of the roof rafters are wooden planks so I cannot really remove these. In summer it gets very hot and in winter very cold. Further to this is the noise when it rains.
The roof is sloping and has further internal beams supporting the roof structure with a depth of 90mm. What is the best way to insulate so:
1. I still get ventilation to roof
2. External sound(rain) is minimised
3. Heat is retained.
4. Is as easy as possible to install (ideally just stuck up or similar)
5. No head space is lost

I know I cannot get the depth recommended (270mm) but something is better than nothing
thanks

 

[PerryOne]

If you do not live in the roof, there is no point in spending good money insulating it.
Far better to concentrate on keeping the heat inside your home.
With this in mind your best bet is to ignore Government guidelines.
Five inches of closed cell insulation saves far more heat than piles of fibre glass.
I recommend that you spray polyurethane foam between and over the joists to get the very best possible insulation at the best price.
One thing about poly foam you can stand things on it without spoiling its effect.
Where you cannot access the roof, then pull off the plasterboard and carefully cut and fit polystyrene sheets.
To make the best job, pull all the plasterboard down and fix one or two inch thick polystyrene or similar under the joists and then re plasterboard and skim coat.