Insulation between roof rafters - Dormer Bungalow.

[Steveb21]

1950s Bungalow with a Dormer conversion done in approx. the 1980s.

Get a fair bit of traffic noise from the sloping roofs in the Dormer areas.
Plaster boarded with wallpaper.
I assume there is no insulation behind this.
The roof rafters are 75cm/3".
What would be the best type of insulation I can do to prevent heat loss and sound proof?

I believe a 25 mm gap will need to be left between the roof felt and and any insulation installed, is this correct?
If so, I will then only have 50mm of area (between the rafters) I will be able to insulate with celotex/Kingspan.
Would I then need to add insulation from the inside in say 50mm of insulated plaster board?
Also, I have heard of Trico Super 10, is this product any good?
Thank you.

 

[Leofric]

The insulation you mention isn't any good as acoustic insulation, Rockwool insulation is better for that. British Gypsum do a 'Soundbloc' board which has some acoustic properties. You need to look at the whole situation to see what level of acoustic and thermal insulation you are trying to achieve. This is where design input from an architectural technician say who could visit your bungalow would help you.

 

[Steveb21]

The insulation you mention isn't any good as acoustic insulation, Rockwool insulation is better for that. British Gypsum do a 'Soundbloc' board which has some acoustic properties. You need to look at the whole situation to see what level of acoustic and thermal insulation you are trying to achieve. This is where design input from an architectural technician say who could visit your bungalow would help you.

Thanks for the reply.
I have got a architect due to come over in the new year to discuss in more detail, I just like to get clued up on things before I talk to the experts.

I have added a few pictures of one of the dormer rooms.
On the picture I have added notes, I have 100mm of space between the hip rafter edge and the plaster board, adding to this is the 75mm rafter behind this sloping wall.

If I leave 50mm for ventilation on the rafter and then add 100mm Kingspan/Celotex so the plaster board will more of less meet with the edge of the hip rafter in the room, acknowledge that the I will lose a little room/ceiling space.

or

could I just add 75mm insulation on top of the plaster board that is already there, and then another plaster board on top?

 

[Steveb21]

Just picking up on this - now I've got a bit of spare time

I am planning to start this shortly on the smaller of the 2 rooms firstly.

Plan is to remove plasterboard from dwarf walls and sloped ceilings.
Install 50mm sound insulating rockwool (on a 75mm rafter - leaving air gap of 25mm) then 15mm soundbloc plasterboard on top. I believe the rockwool has good acoustic and insulation properties as well as being fireproof.

For the low walls although there is access via the crawl space - it is very tight. Don't fancy crawling all around the roof so will rip plaster off from inside the room and insulate - and then as metioned followed by acoustic plasterboard.

Any other things I should consider? Would I need to install a vapour barrier?