gable end insulation u-values

[KayleyH]

We have a 8 x 5m extension, things are progressing nicely and we are doing the bits of work we can ourselves.  It is mainly timber frame (oak frame company) with a mix of brick walls and weatherboarding.  And the 2 gable ends are weatherboarded. 

 

We are trying to find insulation to match the details given on our building regs drawings but are really struggling with the u-values and trying to find a product that matches the requirement ... has anyone else had this experience or know whats best to use .... details from build regs drawings as below.  Many thanks for any advice.

 

(W2) Wall Construction - Habitable Insulated Walls U-VALUE: 0.18 W/m2K

 

Finished externally with horizontal larch, Douglas fir or cedar cladding fixed back to 46x72mm battens. 9mm ply layer fixed to 38x90mm studs with 90mm PIR Insulation between. Internally finished with 62.5mm insulated backed plasterboard to achieve minimum U-value of 0.18W/m²k.

Edited August 3, 2023 by KayleyH

[Dave Jones]

badly planned from the start unfortunately, need much bigger cavity to accommodate todays level of insulation. easiest will be to overboard inside the rooms with 100mm celotex then plasterboard over.

[Conor]

You can fit 22x38mm battens to the inside of the studs so you can fit 100mm PIR in-between. An afternoon with a nailgun. An alternative to 63mm insulated PB is 50mm PIR fixed to the studs, taped, then normal PB. More labour for you but straightforward.