I would have to agree with envirotechure...and I would look it like this - if it is sunny, warm and no wind and you open the door/window you will be warm and so will be the room. If it was sunny and windy, the wind will cause a decrease in temperature and you will be cold and so will the room, so sit behind the closed glass window and you and the room will be toastie. If it is overcast and cold, you won't get any heat from the sun, so close up the room and put the heating on or go back to bed and snuggle up. When the sun moves and it is no longer heating you and the room, close the window and door and go catch the sun in another part of the house. I think we all do that naturally anyway, it's just common sense. And in a really hot summer, you will be wanting to shade that room to cool it and yourself - the exact opposite. Obviously, if you have good insulation, thermal mass etc etc the effect of heating that room will last much longer than that moment, but you will still want to catch the sun in winter and you will want shade in summer.

I don't know why people want to invest in render. If money limited I would always first go with replacing Windows with energy efficient Windows which increase natural light and maximise views or garden trees from interior Plus I'd remove brick fence in front of door as houses where you can see front door always look so much more welcoming as upgrade of workers cottage on these latest dilemmas shows

Those will be very helpful as I will use them straight away!!

Can you post any more photos including the staircase, and how the room next to the staircase is accessed interesting extension not following in the traditional manner of the house, Always follow KISS, keep it simple S for the best result. You could add a traditional front door in black but I don't think it necessary as from what I can see in the photo is the entrance and door already have a lot of character. The lovely Picket will look less fussy if done in one colour quoting Taking the new build/old build divide quite literally, the existing cottage has been redefined as a crisp white entity. In a street of Heritage vernacular, where every architectural shift is picked out in a nuanced tone, this is a drastic departure in itself. Add to this the decision to present the new addition in solid black, and the radical nature of the build becomes apparent (Dulux low sheen black and Lexington white). http://www.wrightsonstewart.com.au/wilston-project