I've done a few the old school way as follows;
1. Strip off tiles, timber lats, sarking, leadwork.
2. Insulate? Total subject on its own.
3. Breathable membrane.
4. Thin plywood.
5. Building paper.
6. Stainless Steel EML.
7. Beads, drip and I put a stop at top butted up to underside of window cill that way you can run a thin layer of clear silicone when render dry for future window changes without cracking render.
8. Choice of render system. S&C or thin coat system.
There are a range of flexible backer boards that will replace steps 3-6.
@Runswithscissors?