St Paul's Boys School

The entrance elevation of the first phase of St Paul’s School development shows the contrast of  solid masonry construction and fine roof detailing.
The entrance elevation of the first phase of St Paul’s School development shows the contrast of solid masonry construction and fine roof detailing.

Strange for a private school that can lay claim to a history going back over 500 years to find itself parked in bucolic Barnes within a 1960s Modernist CLASP structure. 

But it’s plus ça change at St Paul’s west London site, with the first completed piece of Patel Taylor’s 2002 quincentenary masterplan being designed and built by Nicholas Hare Architects. The school’s science block has just opened, forming two sides of a new courtyard and interfacing with a CLASP block destined to be replaced. The new block’s sense of enduring permanence makes it quite a different animal from its reductive neighbour. 

The four-storey building forms part of a new entrance to the school. Its undercroft, below 18 state-of-the-art teaching laboratories, leads to a cloister of shallow pre-cast concrete arched vaults sitting on broad concrete columns. Materials have been selected for their quality – the entrance area’s 75mm thick blocks of self-supporting English sandstone were supplied by Marshalls and built out by Putney and Wood. Ties hold it back to the concrete frame and infill blockwork of the inner leaf; the buff coloured Das Baksteen brick making up the teaching block façade.

St Paul’s main elevation.
St Paul’s main elevation.

The finer roof profile, explains project architect David Tompson, was driven by the desire to reduce the possibility of an overbearing scale relative to the size of the internal courtyard and, on the south, to respond to the demands of the outline planning permission. ‘We did a lot of studies on the building massing but decided that by setting the levels back, we could create what in effect looks like a rooftop pavilion,’ he explains. This resulted in a thin-edge, tapering anodized aluminium profile cantilevering out 2m from a square galvanized frame, tied back to the concrete slab face but resting on 168mm diameter CHS steel columns, which in turn sit on the trabeated concrete frame. The cantilevers shade the aluminium ribbon windows that run 185mm behind the column centres. 

Curiously, vertical cladding was by Red Architectural, while Cristo Cladding fabricated the horizontal profiles. ‘We were concerned that using two different fabricators would lead to inconsistency in the anodizing process,’ recalls Tompson. ‘But we were aware that reflections of the vertical cladding on the cantilever soffit would darken it, so we specified the soffit anodizing two shades lighter.’ It also meant the two subcontractors would not have to try and match anodising from different batches. Thermal bridging through the slab face by the galvanised tapering I-beams was prevented by a 25mm Sarrat thermal break plate behind the galvanised fascia.

The third floor roof cantilever.
The third floor roof cantilever.

The I-beams attach to a 300mm concrete slab roof with downstand. This forms the edge of an inverted biodiversity roof, formed of a Permatec membrane which is laid to 50mm central falls and drains internally through the science labs’ service risers.

The result is a fine, crisp termination to a solidly built structure. Another sharp component is the south block’s fully glazed north elevation, which counterpoints the formal solidity of the main structure in another way. Housing open study and internet areas with views over the courtyard; its nocturnal crystalline brightness would be enough to dazzle sceptical Saul himself.