Because she lives in a single level unrenovated Victorian terrace, architect Julie Firkin has indulged in much idle redesigning in her imagination. So when it came to a commission to amend a similar Fitzroy terrace for a single occupant who felt so space squeezed she was considering moving, Firkin had a whole lot of well-rehearsed moves worked out.

Reshaping the rear of the property with the north-facing courtyard, she avoided the main traps of the bulky box behind claustrophobically dark middle rooms. Instead, she created “a sequence of large and small spaces” that progress up and down a staircase dextrously wrapped around a modern chimney-like structure. This means there is no need for cluttering balustrades.

The graphic ziggurat stairway of engineered oak treads, descend seven steps from the middle living space down to the kitchen/dining on the natural ground level. They ascend five treads up to a partial mezzanine study made for an occupant “who always had her laptop open on the kitchen table”.

Turning another corner of the chimney breast, the stair, which has open-back risers to maintain light and through-views to backstreet vignettes, then rises to the upper two bedrooms, which bring the tally in a small house to three levels, three bedrooms and two bathrooms.

The fluidity of the house, with some spaces (the kitchen galley) having 2.1 metre ceiling heights and the adjacent dining area with 4.5 metres of headroom, was “about making slight divisions of space while still keeping those nice views to the courtyard”. “I was aiming at a feeling of cascading spatiality and rooms that gave the right sense of repose or movement.”

Firkin’s other intentions were to minimize the additions’ impact on the near neighbours and to maintain an atmosphere of calmly appointed liveability. “It’s too easy to add space at the expense of the quality of that space,” she believes.