The existing long and narrow 1950’s end of terrace house has been fully refurbished and extended with the addition of a single-story timber annex. The large garden, with nine adjacent landowners and three mature trees, influenced the proposal. The tree root protection zones determined the use of screw piles and the consequent idea of an entirely timber building, including the foundations. The client wanted to be able to interact with people in the dining and living areas whilst in the kitchen. The side of the house has been opened up to allow a new kitchen to be placed next to the living area. The new dining area sits in front of the kitchen and projects out into the garden. In the main house, the insertion of new stairs has significantly improved upper-level circulation and allowed for more spacious bathrooms. The construction sequence of the customised CLT system was set out at the design stage. The slab-on-stud arrangement uses a waffle slab fabricated from plywood sheets that span in both directions. This reduces at least 30% of the timber used to form the roof in comparison to traditional timber joists or a CLT slab. Between the posts, a ply-formed cassette containing insulation and a vapor sheet has been inserted for bracing, built using a prefabricated flat-pack assembly method. The structure is laid over the acetylated wood foundation ring beam which avoids the need for concrete foundations. The same wood was used to form the external envelope, posts, feather edge boards, windows, and roof copings, meaning that all the components could share off-cut pieces.