A fabric-first design approach was taken to the project, prioritising the upgrade of the entire building envelope as well as a highly-insulated extension to wrap around the existing rear and side elevations. Significant amounts of glazing were incorporated into the design to remedy the under-scaled windows and low ceiling of the original house. This also unlocked the potential for natural solar gain on the western rear elevation, aiding the passive heating of the house.

In order to regulate this solar gain, a continuous steel balcony structure with timber brise-soleil and louvred screens was introduced to the entire rear facade. Integrated growing wires were used to train plants, helping the house settle within its surroundings. The balconies also allow external access from the bedrooms at first floor level and provide views towards a new planting scheme bounding the site. Further to the practical benefits, the balcony provides a central unifying element between the old and new parts of the house.

The whole house was thermally upgraded with the use of external wall insulation that allowed a uniform rendered facade, disguising the delineation between old and new. The existing ground floor slab was also replaced with a new insulated floor slab and underfloor heating throughout . Finally, the existing roof was removed and insulated continuously with the new roof to complete a full ‘blanket’ of insulation around the building.

To facilitate the design, a series of structural alterations were required to support the retained portions of the existing house. These were carefully coordinated between New British Design and Exact Structures to ensure new beams and columns would not intrude on the open-plan spaces.

Due to its location adjacent to the River Thames, the house is located in Floor Zone 3. Despite the floor level of the existing house being set above any historic flood levels, details were incorporated in the design for demountable flood gates to both the new and existing openings. Coupled with this, a solid block construction was selected for the new extension to reduce potential damage caused by water typically trapped by a cavity walls in the event of flooding. The interior of the house will feature bespoke oak joinery throughout, including the principal staircase designed by New British Design and made by a master craftsman Toby Sharp.

New British Design successfully achieved planning permission from South Oxfordshire District Council and were subsequently appointed to provide a full technical design package. This was produced using 3D BIM modelling to ensure clear integration between the existing fabric and new additions.