The minimalist single-story space is an addition to a 1930s house located on a sloping site in the residential neighborhood Dollis Hill, from which the house takes its name. Adopting an unmistakably contemporary design approach, Thomas-McBrien introduced a split level at the ground floor of the existing property to link the house to its garden, which is approximately 1.2 meters below the ground level. The interior is kept simple, with a muted material palette comprising of lightly washed oak elements along with natural stone worktops to enhance the overall natural aesthetic. A deep seating alcove extends along the timber wall into a casement window, which frames views of the surrounding greenery and fills the home with diffused light. Large full-height sliding doors open out onto the garden beyond, where an expansive terrace grounds the extension into the existing slope while inviting residents to linger and relax among the trees.