It is not often that we are given such an exciting and complex challenge! An old retail space with a small dark basement to be converted into two separate spaces: a rentable flat on the lower ground floor and commercial unit on the ground floor. We managed to create a new separate street level entrance to the flat and devised creative ways to bring in daylight and ventilation into the lower ground floor. Our contemporary design around a courtyard allowed us to extend the lower ground floor flat laterally underneath the adjacent building (also owned by the client).
Our client, keen to have a clean modern, open-plan space – a living room with a multimedia wall transitioning into the kitchen, with concrete columns providing a visual distinction between the living and kitchen area. We created new openings in the existing walls to open-up the living and bedroom spaces to the existing courtyard light well, now an attractive patio, with bi-folding and sliding doors opening creating openness and visual continuity across the whole space. In addition, we were able to bring in daylight to the front of the flat through new high-level windows in the lower part to the shopfront’s stall riser (the part below the shop window) and from new pavement lights.
We designed the concrete ceiling with a smooth upward curve, a.k.a. “swan-neck”, to bring further light into the basement. This swan-neck supports the ground floor shopfront windows, creating a generous seating/display area for the shop window.
We designed exposed concrete columns for the new structure, with oak doors and wall panels adding warmth and contrast to the industrial aesthetic. We chose to create an exposed structural concrete ceiling to maximise floor to ceiling heights, (we dug out the floor slab to gain a further 300mm). A new 900 mm staircase was designed to be as wide as possible despite the space restriction.
During construction, we found two vault spaces underneath the pavement level (one possibly used in the past as a bread oven) which we chose to retain to enlarge both a second bedroom and to create a den in the living area. For all our clients we always aim to provide value for money. In this case we are proud to state that the client was extremely satisfied with the outcome. We achieved a 61% expansion in the gross internal area which increased both the rental income and also the long-term investment for our client. Due to the high-quality finish, he had no problem finding immediate tenants for both the flat and the now commercial space [now Class E] on the ground floor.
Technical information
Structural challenges
The property needed extensive underpinning due to shallow 19th century foundations. An existing beam and two chimney breasts were removed to gain space, and exposed concrete columns were added. Some original brick walls brickwork around the light well courtyard needed re-building in concrete, with steel lintels added to make the folding doors as wide as possible. The whole front pier (holding the weight of the 4-storey building) had to be supported by temporary works while the ground slab was taken away and a new beam cast.
Mechanical Ventilation and Heat-Recovery
We installed an MVHR unit to control ventilation and airflow to the basement area which runs 24/7 delivering an 89% thermal efficiency heat exchange and ensuring that cooler air enters the property on warmer days while also extracting moisture from the bathrooms and kitchen areas. This has a positive effect also on the maintenance of all the concrete structures.
Sustainable Urban Drainage System
As part of SUDS, to reduce existing dischargerates by 50%, the whole courtyard was built with a water attenuation system so as not to overwhelm the public sewer. The courtyard now achieves 4.3 cubic meter water storage, which is greater than the 3.4 required.
Fire + specialist waterproofing systems
Due to the open plan design, we chose the Plumis Automist system, which will spray a fine mist of water only when set off by a multi-criteria alarm followed by a heat sensor algorithm, so will not go off due to just smoke. A specialist Delta system for waterproofing and drainage (with insurance backed guarantee) was part of the specification.
Futureproofing
The new extension was built with foundations designed to take the load of not just the existing building, but also 2.5 extra storeys for a possible vertical extension of the flat above, should the opportunity arise in the future. An SVP [soil vent pipe] was also incorporated into the basement at this stage to prevent any disruption to the flat later-on.
