Recommended depth of insulation

[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

 

[DevilDamo]

What is this for... to make the habitable space warmer or to cut down on energy bills or a mixture of both?

 

[johnjones323]

Both

 

[jeds]

Insulation works on the law of diminishing returns so it is true that the first 50mm will save you more than the last 50mm. But you should really look at it in terms of overall service of the insulation. The balance changes dramatically when you punch in higher energy costs. You know energy is expensive now but it will get proportionally more expensive in future years. It wasn't all that long ago when 100mm of loft roll was considered good insulation - in fact a lot of people still think that is the standard. In fact 300mm is more like the minimum now, and in the not too distant future that will be cosidered low.

 

[mointainwalker]

Fibre-wool gives a much better financial return than insualtion board. Its insulation properties are 60% of the board for only about 20% of the cost but the board is easier to fit in this situation

How deep are your rafters ?.

 

[johnjones323]

3 inch rafters, I have used that up with the currecnt insulation I have installed.

 

[Deluks]

what are you using the attic for? Plasterboarding the rafters is only an option if you are converting the attic for habitable use. ie: can of worms. No lid.

 

[DevilDamo]

As per their first post...

My attic is has living space