This was a response to a forum thread (elsewhere) and something that has been touched on in an earlier blog.
I designed a small mock coach house, at the end of a very long garden. (It was mock to the planners, and a possible nimby backlash, and their were no coaches) The site was less than 5.6m and agreement had been reached to build on the boundary thus leaving an internal width of 3.6m. Plainly there were no projections over the neighbour's land and the wall and gutters etc were designed to be virtually maintenance free.
One trick (such as it is) is to create the main entrance half way along, into the side, rather than front.
If necessary, the daylight can be dealt with internal courtyards...see Peter Phippen's project in Hatfield for a terrace of very narrow houses...https://www.themodernhouse.com/wp-content/uploads/2017/10/THE_RYDE-TMH.pdf
Thus, anything is possible within the blessing of planners and neighbours... a gift of a bottle of good whisky works wonders (obviously not to a planner!)
So, don't discount a narrow site...all problems are an opportunity: the wise tell us! huh