Insulation Between Rafters

[AndyNewBuild]

Hi All,

In the middle of a new build and starting to look at insulating the roof. I can squeeze 150mm of insulation between the rafters but am wondering which method is best.

I'll be using foil backed insulation board but have the choice of one single layer of 150mm thick board or two layers of thinner board totalling 150mm. Anyone any advice at which method will provide the best insulation? Obviously having just one layer would make cutting easier!

Thanks for the advice.

 

[Deluks]

Flat/pitched? Habitable room or attic space? U values shouldn't make a difference either way if using only 1 type of insulation. Whatever works out easier/cheaper for you.

What is important it to overboard under the joists as well, 20mm will suffice.

 

[AndyNewBuild]

Thanks for the reply.

It's habitable space and it's a pitched roof. I will be using insulated plasterboard over the rafters.

It will work out cheaper to use one thickness, and easier!

Thanks.

 

[Chukka63]

have you tried cutting 150mm boards between rafters???.

 

[AndyNewBuild]

have you tried cutting 150mm boards between rafters???.

Not 150mm but have cut 100mm between rafters without problem. If you measure the gap for each cut, use a fine tooth saw and cut at an angle to give a snug fit, it's quite straight forward.

It certainly saves time rather than cutting two separate layers.