Sandy Rendel Architects Ltd 

the house was constructed using a lightweight steel frame on a piled slab. The steelwork was prefabricated as a series of portal frames that were craned down the alley and site-welded together. Given that every inch in such a narrow space was valuable we chose to fully weld the connections and express the frame internally, even utilising the depth of the steels to maximise the space.

https://archello.com/project/the-slot-house