The project site is located in Crouch End, North London. The home sits adjacent the Parkland Walk, a tree lined pedestrian and cycle route following the course of a disused railway line, running between Finsbury Park and Alexandra Palace.
The house is fairly traditional of the London area, built from brick in the late 1990s on a narrow plot.
The brief was to design a side extension to replace a dilapidated conservatory. The aim was to give the addition a more generous and naturally lit living space, which would be accessed off the kitchen. A further goal was improving the connection from the house to its garden. The new extension will also be used occasionally as a yoga studio.
The site is in a conservation area which is typified by large Victorian houses, interspersed with modern apartment blocks. From a planing perspective, the aim was to keep the extension low to the existing fence and discrete from the street.
Besides planning, a key constraint was the large beech tree growing very close to the house. The proposal, and delivered design, was to create a lightweight timber structure that made use of the existing foundation from the defunct conservatory. This would avoid the risk of harming the tree’s roots from excavation or piling.
The plan is based off the geometry of a perfect square, with columns in each of the four corners forming the basis for the grid. The structural members define a simple, well proportioned room.
The floor running through from the main house has been replaced with engineered oak. The floor in the extension has been laid with under floor heating.
The floor, end walls and roof are all heavily insulated to combat the cold London weather.
The design of the structural frame was refined in close collaboration with Devon based specialist timber frame contractor EmanuelHendry. The main frame of the building was prefabricated off site in their workshop, where it was pre-assembled to ensure an accurate fit on site. The frame was made from Canadian Douglas fir timber, which was imported from Canada. The fabricators were then able to pre-assess the frame for structural integrity, before partially dismantling it into large pieces. It was then brought to site on a truck and craned into place over a single morning.
Each side of the square plan has been divided into three equal bays, with intermediate columns set out in thirds along the span, to reduce the depth of the perimeter beam. In essence, the simple planning grid was designed to portion up a square into a more dynamic space. The four columns sit on a 4.8 x 4.8m planning grid, which is then subdivided into 3 bays of 1.6m each. That dimension divides again by four into rafters at 400mm centres. The grid results in a nice quick rhythm to the roof structure.
The columns have been set in 100 mm from the external skin. The perimeter beams spanning between columns have an upside down 'L' shaped profile, with the short leg fixed to the ply, allowing the gap between structure and cladding.
A deep central ridge connects two of these third points on a diagonal line, creating an axis from the existing kitchen door to the garden’s side entrance gate. Rafters span from the glazed side walls onto this diagonal beam. This geometry creates two roof planes which appear to be rising on one side whilst falling on the other, but are in fact both at a constant pitch. Down the two side elevations are sliding glass doors, also divided into three. Triple sliders allow 2 thirds of each elevation to be opened up to the garden.
Structurally, the existing two storey brick house acts as a stable anchor to one end of the extension. Left unrestrained however, the opposite end would want to sway under wind or snow loading. The external vertical cladding is fixed back via battens to an insulated plywood wall. The plywood acts as a brace to this end of the plan.
Sliding doors and cladding to the end walls are all also crafted from Douglas Fir, with a hand oiled finish. The roof framing, cladding and enclosure was completed over a two week period in winter, with the project finishing the week prior to Christmas 2019.