Hi Louise. In the end we merely added new windows and a new door. We went for a mixture of Sapele and aluminium to break up the width of the house. The windows are made by Smart and are the Alitherm Heritage 47 range which are supposed to a close match to Critall. We also converted our garage and matched the windows and use of Sapele frame as well as having a bespoke Sapele gate. We're still not convinced we made the right choice by adding two sapele windows - but we always have the option to add aluminium ones to replace them and they are not too costly. So - it's not 100% what we wanted, but for the budget we had we are very pleased. The garage conversion is very cool inside with bespoke ply shelves/desk and seating area as well as ply walls. It is a homage to Corbusier and his Cabana in South of France :)

Completely agree with Jonathan. I have seen a couple of 70s houses modernised fantastically in my area, both with some type of grey/grey wood cladding in parts. It retains the 'character' (I'm sure in 50 years time this architecture will be to die for!) whilst giving it a modern twist. I also think the house is very 'garage heavy' so I would get a really modern garage door (possibly wooden) and try and have a balcony above to distract from it. See this fab example... [https://www.houzz.com/discussions/how-to-modernize-my-mid-century-split-level-house-exterior-dsvw-vd~3882230[(https://www.houzz.com/discussions/how-to-modernize-my-mid-century-split-level-house-exterior-dsvw-vd~3882230) This would only work if you extend fully over garage as Jonathan suggests, and would obviously require pp. Could be a fab master bedroom or upstairs living space if you did it though :)

You could consider matching the existing white render to whatever is used on your new extension. If you chose timber cladding, I could suggest something lighter, maybe a larch/Douglas fir/oak(/Marley board as suggested - as budget allows) with a protective UV oil coating (most people do not like the weathered timber look). You could then wrap this cladding over the existing area of white render across the corner and wrapping the garage also. This would give a very modern look that ties the house together, and given the area of the garage is actually fairly small (once the garage door is discounted) the cost would be minimal. If you are set of replacing the windows, ensure you pain the garage door the same colour. This is a really cheap change but again will help tie all together. However, for the cheapest option, just using white render on the extension, will also work. This negates the requirement to over-clad perfectly serviceable finishes on the rest of the house. N.B. Any changes to the front of the house may require a re-submission to the council for amendments.

P.s. I would measure the roofing tiles too given half a chance. So you can assure yourself all colours on the exterior work well together. (Even if a roof tile looks grey to you, it still belongs to one of those hue families,,,,why fight with it when you can harmonise?) 🤓