Tldr What's the approximate cost / range of a small side extension say a bedroom size 3.5m x 2.5m and adding a shower to a guest wc in London?
I live in a semi-detached house in travel zone 3 in London. About 2000 sqft on 3 floors incl converted loft, with a small garden (quite small - about 1000 sqft). I haven't done any work to the house - it came with a small extension- a utility that adjoins the kitchen and goes to the wall shared with a neighbouring block of flats. So there is no through access to the garden - see image - the top is the front and the bottom is the back of the house. there is space between the front of the house and the utility.
My father visits a few months a year and navigating stairs to the first floor is getting difficult for him. I am considering extending to the side to make a small double bedroom made, and to add a shower to the wc by extending out.
I still want a small courtyard left open to the side between the utility and the new bedroom so the kitchen gets light and I have space for a shed.
What is the current rate / range for labour and materials for such a refurb, including design, electrics etc.? It would need to be done while we are living in the house (cannot afford the cost or hassle of moving out). Some people seem to go for modular extensions but I'm not sure if this is permitted to the side or if it would be significantly cheaper - in any case I will need planning permission.
I'm not looking to recover the cost of this when i sell since likely not planning to downsize for several years, I hope. But need to figure if my budget will stretch to it.
Thank you.