Insulating the rafters

[trowelandhawk]

Hi everyone.
I am using this time I have to sort out the loft and then start boarding out, beaux etc etc. Looking at the roof underlay it is not breatheable by the look of it. Which leads me to next question.
Aldi are doing insulation quilt blanket at the moment at reasonable price hence me starting project if it’s doable...I was going to tack this to the rafters then seal joins, batten on top of rafter then plasterboard that. I just have a nagging feeling that I can’t do it because the underlay needs to be of a breatheable type ie tyvek or the like.
Some help / advice would be appreciated.
Thankyou all.
Keep safe

 

[Alastairreid]

You will need to introduce ventilation between the quilt and tar felt at eaves and ridge..
Fix a vapour barrier above the plasterboard.

 

[trowelandhawk]

I have seen a sort of ‘fag packet’ diagram.. if I understood you correctly then I will install as follows..
1. Foil blanket tacked to rafters and Aluminium tape over joins.
2. Batten on top of rafters
3.THEN ADD A VAPOUR BARRIER(plastic sheet roll ?).tape up joins.
4. Install plasterboard.

Forgive the questions. I just want to be sure. If I do a job it will be correctly and once. Not a diy cowboy. If it’s not in my limit I not gonna do it.

 

[datarebal]

that is 1F and not breathable

 

[trowelandhawk]

Sorry... the red is meant to signify the vapour barrier on top of batten but before plasterboard

 

[Alastairreid]

If you're insulation is the foil type and you tape the joints you can omit the vapour barrier above the plasterboard.
Open the overlaps in the felt to introduce some air in the cavity.

 

[catlad]

Type manthorpe felt lap vents into ebay
I would also recommend using foil backed plasterboard.

 

[trowelandhawk]

Thankyou.
The manthorpe felt lap vents look a great idea. Simple always works and simple ideas also make people millionaires!!. I was going to get foil backed insulated plasterboard in answer to you yes.