Is Non-foiled PIR insulation suitable for roof insulation?

[Dunmow]

Hi I am doing a self-build and we are currently installing the roof.

 

Our roof build up is planned to be

 

slates
to 50 x 25 pre-graded battens
to Cromar Breathble Membrane
to trussed rafters 150mm

 

We want to put 125mm PIR insulation in the trusses and then 100mm PIR below the trusses (no gap)

We have been offered non-foiled 100mm PIR insulation which are slight seconds. We want to combine this with 25mm foiled insulation and put both inside the trusses (to achieve 125mm). Will this work? Or is it better just to use 100mm foiled insulation inside the trusses?

[Iceverge]

I'd avoid PIR in the roof if I could. Especially between timbers. 

 

Mineral wool, woodfiber or cellulose would be better. I went on a bit if a rant here. 

 

https://forum.buildhub.org.uk/topic/23894-u-value-for-solid-wall/?do=findComment&comment=369038

 

 

[Patrick]

On 19/11/2021 at 21:03, Iceverge said:

I'd avoid PIR in the roof if I could. Especially between timbers. 

 

Mineral wool, woodfiber or cellulose would be better. I went on a bit if a rant here. 

 

https://forum.buildhub.org.uk/topic/23894-u-value-for-solid-wall/?do=findComment&comment=369038

 

 

Second that. Pir also terrible sound insulation. That's often forgotten.