https://www.greenbuildingstore.co.uk...ent-retrofits/

Well worth a read as it shows the detailing for EWI on the outside face of the wall.

If you are installing a good triple glazed window (eg Uw value around 0.8 W/m2K), with bad installation details then the overall heat loss of the window can be doubled to an effective installed Uw value of 1.6 W/m2K or more.

This is a critical piece that applies to all such work when using high quality products.