Explore I Blog I Out of Thin Air by Matt Somerville

Our new Clore Learning Centre for the Roman Baths in our home city of Bath is the product of a long and complex process which has brought new life to a group of overlooked and dilapidated buildings in the heart of the UNESCO World Heritage Site. A new rooftop room is the most prominent outward signal of these changes, but it has been designed to reflect the site’s character and industrial heritage.
The buildings we adapted and re-used were built in the late nineteenth century as the “engine room” of new spa facilities on the Roman Baths site: a steam-powered laundry, boiler house and warehouse. The black smoke that belched from the elaborate boiler house chimney as its pumps lifted spring water to a rooftop cistern was the cause of many complaints at the time. But, from this tank, heated and pressurised water was supplied to the spa treatment rooms through the York Street archway – both arch and aqueduct, as it turns out. Like so many things in Bath, it’s all about water.

In 2011 when we first visited these buildings, their industrial character had been eroded. The coal-blackened interior of the boiler house was hidden behind plasterboard and its roof-level water tank demolished. This loss, however, provided an opportunity: to re-occupy the spatial envelope of the tank to provide a much-needed lunch room for visiting school groups, with an elevated and unique outlook over the roofs and backs of a densely built-up urban setting.
We wanted the new rooftop volume to evoke the lost tank and its purpose as a container for hot water from Bath’s “Sacred Spring”. It should also be legibly new, a lightweight and light-filled counterpoint to the mass of Bath Stone masonry on which it’s set. Our first concept image tried to capture this: steam rising from the thermal spring; a sense of misty insubstantiality.

The new room needed to be thermally efficient. This suggested that most glazing should face the street, with other walls largely solid and punctuated by windows framing particular views. However, we would need a treatment that could unify or mask the placement of wall and windows: more sculptural abstraction than architectural composition. Our solution was a two-layer façade with a translucent “veil” of perforated aluminium panels, a visual foil, overlying a weathertight and cost-effective envelope. The opacity of the veil would respond to the presence of windows behind it: more open on the glazed front of the room, more closed on the other three sides. It would filter light, acting as a brise-soleil, and screening views of neighbouring properties across the street.
To achieve a mist-like effect we would need to give the panels a sense of gradation or dissolution. This would rely on a pattern of perforation that could transition from solid and visually opaque, to open and relatively transparent. Panels in front of windows should give a filtered view out, while also controlling solar gain; those in front of solid walls should be more closed, concealing the underlying construction.

To give a naturalistic effect of mist, our cutting pattern needed to be bespoke and non-repeating rather than linear and mechanical. For laser cutting, it doesn’t matter whether every hole is the same or whether they’re all different. Our challenge was that the panels would have about a quarter of a million perforations, more than we could possibly draw without resorting to standardisation and repetition. We had to find a way of converting our photographic image of mist into a CAD-format cutting pattern that would give the overall composition of a more natural effect, rather than the mechanical one that would have resulted from a simple, linear gradation.
To add another layer into the composition, we drew a geometry of tessellating fan-like shapes as our organisational device, rather than a simple grid. This could be interpreted as the laying pattern of a mosaic, of the granite cobbles in front of the Roman Baths or, perhaps, as stylised cloud or waves (in its Japanese origins it is called seigaiha, meaning ‘blue sea waves’). It adds another visual layer that is only revealed on closer approach to the building or, of course, from the interior. This sense of a subtly shifting appearance according to the viewpoint and light conditions varies and enriches the experience of the building.

To overcome the challenges presented by this complexity we needed parametric design, an algorithm that could generate a pattern according to a range of parameters defined by us. The technical solution was provided by Dr Paul Shepherd, Reader in Computational Design at the University of Bath. He programmed software that could produce vector-based CAD drawings based on grayscale raster images. For our panels, we used photographs of natural mist or cloud. The software package was programmed to draw large holes where the generating image is dark, small holes where it is light.

The resultant drawings were, with a bit of finishing to add margins and holes for bolted connections, sent directly to the specialist metalwork contractor for laser cutting. Every panel they produced is unique and corresponds to one slice of the generating photograph.
Now the panels are installed, we can see how their appearance changes through the day under different conditions of light and weather. The curved profile of the panels picks up light in different ways and their bronze-tinted anodised finish grounds the new volume in a street and a city of light-coloured limestone.

Matt Somerville

Images
1. View down Swallow Street\, with the Roman Baths Clore Learning Centre on the left
2. Archive image of the old boiler house in the 1980s\, before the removal of the Victorian water tank
3. The hot spring at the heart of the Roman Baths site: early design concept
4. A photographic image used to generate the cutting pattern
5. Geometry & parameters of the cutting pattern
6. Cutting pattern & detail for panels of the street elevation
7-9. The installed panels c. Rebecca Noakes