Please help!! Insulation depth?

[johnjones323]

until last week I had no insulation at all in my 1896 house. My attic is has living space and I decided to put 65mm insulation board between the rafters.
I have read that they recommend 120mm of insulation board but cant find any fact that justifies me do increase to save money. http://www.energysavingtrust.org.uk...ducts/Home-insulation-glazing/Loft-insulation

they basically say that its the first 50mm that saves you. It will cost me a further 300pounds to cover the whole area again.

Is it worth it?

Second question
If I was to do it could I just use 75mm plaster board screws to hold them against rafters then plasterboard them with 100mm plasterboard screws. Is it ok to have the rafters hold 65mm insulation board and plasterboard?

Regards

John

 

[freddiemercurystwin]

Well it will keep your loft warmer but not twice as warm. What size and spacings are the rafters? Probably quite small given the age although its pretty lightweight.

 

[johnjones323]

Hi.
Rafters are around 35cm apart. the room is 7 meters long.