Posted By: maxsmour dreams of floor to ceiling South facing glass will lead to overheating. I understand external shading is the best way to tackle this

Correct and correct.

we are looking at either motorised external blinds or some form of brise soleil (ideally retractable)

Why do you need a retractable brise soleil? If placed the correct height above the window and of the correct width they are automatic in operation. They allow full sun into the room in winter and block the entire sun in summer. Calculate dimensions for the brise soleil so April is right on the edge. I finally put one up last year - just the aluminium frame for it and put some hessian over the top, which I've left for now because it works so well.

Blinds depend on the type of window you have. Are they outward or inward opening? Or fixed? Flyscreens are moderately effective as sunscreens as well. We got them from streme. Internal honeycomb blinds also work surprisingly well, because although the heat is inside the house, it transfers to the air in the house and is exhausted by the MVHR a lot more easily than if the sun shines on the floor and walls, or furniture etc.

edit: to add that PHPP has a summer overheating worksheet, so if it's possible to run that it may give you a better idea of the size of the problem and whether any proposed fixes are likely to be effective. Other packages may do a similar job; I just don't know.

thanks you both that's really useful