The garden of this north London house was the final phase of a large refurbishment project. The client wanted a serene retreat for yoga set in a ‘tropical’ garden. The building needed to have a sense of solidity and permanence yet be open to and part of the garden. It had to be better than off the shelf garden rooms which were rejected on the grounds of flimsiness and restricted openings. The site is a conservation area and therefore the building had to be built without requiring planning permission (permitted development). The area was also surrounded by mature tress with shallow roots, making traditional strip foundations impossible and had to resist the spread of fire across the garden boundaries which is was adjacent to on two sides. The structural solution for the tree roots was to cast 3 sides of a cube in reinforced concrete. This acts as one and was cast straight onto the ground - the whole building floats over the roots. The 2 walls are left exposed internally and were cast with meranti board formwork that matched the surrounding fence. The boards were used for three lifts, then cleaned and charred to be reused as a flexible boarded ceiling under the incredibly thin (100mm structural zone) steel roof that cantilevers over the fully openable sliding corner glazing. All 6 panels slide to give flexibility The copper roof gives the building a refined elegance that is visible from the upper floors of the house so had to be beautiful.