Hi, I'm looking to replace my roof completely so will do loft conversion at the same time and I want to add PIR or phenolic insulation over rafters and I'm wondering if I can also add mineral wool in between the rafters to make it even warmer and increase sound insulation. My only concern is if I will have any condensation issues as in theory mineral wool and air will be trapped in between VCL and PIR which is also a VCL... Any advice?
PIR + Mineral wool
- Thread starter Hosti3000
- Start date
You would generally put PIR in between the rafters with a 50mm gap to the underfelt and 25mm PIR over the underside of the rafters so for example 150mm rafters would accept 100mm PIR maintaining the 50mm space and 25mm PIR underneath gives you a total of 125mm PIR followed by plasterboards and skim.
An all PIR setup isn't the best if sound absorption is wanted. It's terrible for that, so having a thick mineral wool layer behind the PIR would work great for that.