The apparently simple form of Robin Partington and Partners’ Park House conceals complex and subtle geometric relationships, writes Felix Mara
Call me blasé, but as a born and substantially bred Londoner, I’ve always found 99 per cent of the architecture of my home town’s main shopping thoroughfare in Oxford Street unmemorable. But that percentage has been diminished by the arrival of Robin Partington and Partners’ Park House mixed-use development on Europe’s busiest shopping street. With a 145m frontage, it dominates surprisingly distant street-level viewpoints. On technical grounds alone, and in particular for its engagement with glass technology, it would warrant at least a paragraph in Pevsner.
There’s a rationale behind Park House’s geometry. Its unifying form identifies it as a singular entity on a similar scale to Daniel Burnham’s Selfridges across the way. Radiused edges soften its form and, with its crouch-backed roof geometry, Park House bridges the leap in scale between its eastern and western neighbours. Inclined facades optimise the balance between ground-level pedestrian space, and floor area for the offices and flats above the shops, and its tapering plan form accommodates the office entrance at its west end. The outcome may look simple, but it involves complex and subtle geometric relationships, and cladding components needed to be rationalised to keep a handle on the cost and programme. Parametric software, initially used by Robin Partington and Partners to convince the project team that Park House was a viable construction proposition, was invaluable and it picked up Bentley’s Be Inspired Generative Design award in 2012.
First, Robin Partington and Partners used Bentley Generative Components parametric software and Bentley Architecture to refine the setting out of the external envelope, producing a network of dynamically linked geometrical relationships. The top surface of the roof and each of the four facades were defined as tori which intersect to generate the overall volume. These tori have radii as large as 2.5km, and the radius and locus of each torus was adjusted to fine-tune the building’s geometry according to its rationale. The four facade tori all have the same radius, optimising panel repetition economies. The junctions where the toroid surfaces of the facades meet were defined as a series of cones which are tangentially related to the gently curved surfaces of the principal facade plane, and also rationalised panelisation. ‘The main area of complexity was the fillet zone between the facades and the roof,’ says Robin Partington and Partners’ project director Paul Rogers. Here, the facade tori have to blend with the roof torus, and software which enabled these local relationships to be quickly appraised and refined was essential.
The next stage involved defining the size and geometry of the glass and aluminium panels used to construct the facade and roof. The vast majority of these panels, including those on the roof, were double-glazed units. There are, of course, cost premiums attached to bent - and in particular double-curved - glass panels, driven by a hit-and-miss manufacturing process which involves remaking units whose geometry is outside the required tolerances. However, it was possible to cold bend approximately 80 per cent of the panels on site rather than heat bending them in the factory, and this was beneficial to the cost and to the programme.
Robin Partington and Partners also used Bentley software to maximise the number of panels which could be cold bent and to optimise their size. This modelling process resembled a complex equation which enabled the architect to evaluate the essential variables: reducing the size of panels (and therefore their bow) to achieve a closer approximation to the curved setting out entailed more junctions, which carries a cost penalty; pronounced faceting is potentially visible and offsets between adjacent panels, especially at corner intersections, not only create visual ‘ping’, but are more difficult to construct and make weather-tight.
This parametric modelling was just the beginning of an elaborate reiterative process of appraising and developing the surface geometry of the cladding and secondary support structures, as well as the interface between the two, which involved cladding specialists Seele and Focchi. But it was an essential stage in the project, without which Park House would have been more angular, less transparent, or even both.