Insulation spec for under rafters

[tvrjohn]

Hi
Re-surrecting an unfinished project in an 1820s farmhouse where i submitted a Building Notice in Sept 2007 for a loft conversion to make it into two habitable rooms.

How can i establish the spec for insulating beneath the rafters ?

rafters only 3" x 2" so i will need 50mm air gap to start with,

option 1, can i run GEN-x Insulation blanket straight onto rafters then batten then plasterboard ?

option 2, batten the rafters to make them deeper to fit sheet insulation boards 50mm thk ? or rockwool ? then blanket, then batten then plasterboard ?

Please Advise

 

[Ian H]

How much headroom do you have?

I’d do a full layer of 100mm Celotex under the lot.

 

[foxhole]

Agree 100mm celotex.