Wooden Annex

We fully refurbished the existing 1950s end-of-terrace house and extended it with a single-story timber annex. The large garden had 9 different adjacent landowners and three beloved mature trees, all of which influenced the proposal. The tree root protection zones on the site determined the use of screw piles and the idea of an entirely timber building, including the foundations.

Our client’s wishes initially didn't fit with the existing long and narrow site. They wanted to interact with people in the dining area and the living room while cooking in the kitchen. So, we placed the kitchen next to the living area through a new large side opening from the existing house and positioned the dining area in front of the kitchen, projecting it out of the main house and setting it in the garden.

The main house was reconfigured with new stairs, significantly improving circulation to the upper level and providing more spacious bathrooms. We customized the structure and set out the construction sequence at the design stage instead of using the more common CLT system, prepared by a manufacturer or a conventional wood frame system. Our structure, a stud wall arrangement, uses a waffle roof slab fabricated from plywood sheets that span in both directions. This reduces at least 30% of the volume of timber used for the roof compared to traditional timber joists or a CLT slab. Between the posts, a ply-formed cassette containing insulation and a vapor sheet is inserted for bracing, built using a prefabricated flat-pack assembly method. This structure is laid over the acetylated wood foundation ground beam, avoiding the need for concrete foundations. The same wood was used to form the external envelope, posts, feather edge boards, windows, and roof copings, allowing for the sharing of off-cut pieces between components. Over 1222 individual pieces were produced digitally for the structure and envelope, which were assembled on-site using traditional carpenters' skills.

If the annex had been built using conventional brick and steel construction, the embodied CO2 would have been 70% more. It also used less timber compared to conventional methods. Our positive step is marginal, but small domestic projects dominate the majority of the UK construction output, so the communal contribution could be significant.

*10386 Kg CO2 (brick, steel, concrete footing version) against 3075 Kg CO2 (Wooden Annex)*