The UK's first Energiesprong homes

[kenneal - lagger]

On a new build it's even cheaper, easier and still more efficient to insulate externally.

(Edited once to add efficient)

I'd have to see the data on that.
New builds on the high end here are going with a 19mm insulating board on the outside between the wall sheathing and the exterior siding with 200 mm of insulation between the studs (some have an air gap between a 138mm outer stud and a 50 to 90mm inner wall to support the giprock surface. ) Doors and window ledges have to be beveled to reach through the wall thickness as preformed door casings have yet to be adjusted to fit these new thicker wall sections.

Structurally on most domestic builds in the UK a 100 stud is all that is required, although sometimes a 150 stud is used with a fibre insulation to get the required U-value, and it would be easier to put all the rest of the insulation on the outside of the sheathing with the cladding over it. This ensures that there is no interstitial condensation in the structure which can happen if you have more than half of the insulation within or on the inside of the structure . When using a timber frame in the UK it is usual to use a single leaf construction. An extended cill and surround is necessary but is just a function of the additional wall width.