Church services

The First Church of Christ the Scientist in Belgravia was regularly attracting congregations of over one and a half thousand in its heyday. Completed in 1907 just off London’s Sloane Square, the building’s mix of Byzantine, Romanesque and Indo-Saracenic detailing ensured it a distinct status within the Chelsea townscape. By the late 80s however the once sizeable congregations were dwindling, until in 1990 with just a handful of followers the church closed its doors for the last time.

Now, after a two-year transformation the building has re-emerged as the first major music and arts centre to be launched in the capital for 25 years. What’s more after almost 60 years of nomadic existence the Royal Philharmonic Orchestra will use it as its first permanent home.

The renovation began in 2000 when Cadogan Estates bought the church with the intent of creating a public arts and cultural facility ‘befitting the buildings scale and character’. Architecturally the refurbishment, carried out by London based practice Paul Davis & Partners, was relatively restrained due largely to the church’s listed status. English Heritage has been heavily involved in the scheme all along, keen to preserve much of the original fittings and finishes including the leaded and stained glass windows, the former organ screen and the ceilings with their detailed mouldings.

The building’s transformation however benefited from the existing raked floor installed in the large galleried auditorium. In total this provides seating for audiences of 980, 480 in the stalls, with another 500 in the surrounding balcony. Building services consultant and client advisor Voce Case (now merged with the Environmental Engineering Partnership) drew up a scope of works for Cadogan Estates. This focussed on the fact that the hall would primarily be used by the Royal Philharmonic Orchestra as a rehearsal and recording space: a new stage capable of holding an entire classical orchestra of up to 100 performers was needed, as well as specialist lighting and acoustic treatment. However, it also needed to take into account that the hall would be available as a venue for other events including jazz, classical music, dance and film exhibitions. In addition provision was made within the building for a discrete exhibition space, bar and catering facilities. All of this was to be available on a seven-day-a-week basis for use up until 11 o’clock at night.

Partly because of the complex co-ordination issues that existed, Cadogan Estates decided to tender the project as a contractor designed scheme, with Gratte Manly undertaking the design, installation and commissioning of the all the mechanical and electrical services.

Ventilation and air conditioning

Fitting plant into a building that was never designed for modern mechanical services is a common challenge, and in the case of Cadogan Hall one that was amplified by its listed status – which prevented any major structural alterations. In fact the original church did have a mechanical ventilation system, driven by a large Mather & Platt fan housed in the building’s basement. This forced fresh air into the main hall through grilles set in the Church’s raked floor and the large void that existed beneath this has subsequently governed the way in which the main auditorium space is now ventilated.

The design team were looking at internal design temperatures of 20°C during full house performances and opted for a fully air conditioned, 100% extract system. Colin Stafford, technical director with Gratte Manly points out, that in plant terms it was like fitting a quart into a pint pot. “There was no space for conventional air-cooled plant and even if there had been we had the added problem of strict noise break-out limits due to the surrounding residences.” The design team instead opted for an open water-cooled system, with chillers located in the basement along with the rest of the primary plant. “Then we had to find somewhere for the cooling tower,” says Stafford. “The intention back in 1907 was to fit bells in the belfry, but this never happened. So we looked at whether we could install the cooling tower there.”

After playing around with the sizings a 400 kW Baltimore Aircoil cooling tower was installed within the belfry space – craned over the building in sections and slid into place through the existing openings before being assembled. This runs on a continuous water flow of around 17·5 litres/s with an inlet and outlet temperature of 37°C and 31°C respectively. Noise limits were a particularly sensitive issue given the proximity of surrounding apartments and the likelihood that the cooling tower will be operating late into the evening. Maximum background noise levels could not exceed 2 dB above the existing noise levels of 43 dB on Sloane Terrace and 40 dB along Wilbraham Place, giving an overall target of 45 dB. New louvres have been fitted in the existing openings of the belfry and behind these vertical splitter silencers are installed on the three sides where air is rejected with further sound attenuation on the air inlet of the cooling tower.

In the basement plantroom two 190 kW, R407C chillers pick up the cooling loads. For ease of installation in the tight space, upvc pipework has been used for the condensing water runs. This rises up through a lightwell to the belfry, a total height of around 30 m that required a larger than usual set of condenser water pumps. Vaults underneath the road off to the side of the plantroom have been refurbished to contain the water treatment plant.

Air handling is taken care of by two Holland Heating units, brought flat-packed into the space and built in-situ, one on top of the other. Supply air is drawn in from a lightwell below street level, with the lower unit serving the ancillary and back of house areas, while the upper unit supplies the main theatre, including the stage, auditorium and balcony.

There are four general scenarios for controlling the ventilation. One is purely for the back of house areas, which includes the main function room, exhibition rooms, dressing rooms and back of house accommodation. Two, three and four all encompass the main hall but to varying degrees. Two is for rehearsals and comprises of back of house plus stage; three is for smaller performances and includes, back of house, stage and auditorium; while four is for full performances with back of house, stage, auditorium and gallery.

For the main auditorium fresh air is supplied at 18°C using the plenum beneath the raked concrete floor. The terraced seats are arranged in banks of four with air delivered from the void via a slot cut into the concrete slab. Air enters each box structure forming the terrace and is then introduced into the space through the seat pedestals.

A lack of test data on the pedestal seats convinced the design team to run a mock-up at BSRIA to determine the exact ventilating characteristics of the pedestal set up when used in the hall. Ultimately they were looking to achieve 8 litres/s per person and it was determined that this could be achieved by pressurising the void to between 15 Pa and 25 Pa, depending on occupancy. The mock-up was also used to alleviate concerns about draughts around the feet and legs of the audience. As it is the perforations are restricted to either side of the pedestals, although in practice the incoming air is barely noticeable.

Air from the hall is taken out at high level through extracts installed on either side of the six translucent laylights. Two variable speed axial flow extract fans are located in the loft space above the auditorium. Save for a new copper roof, the loft has been left largely intact, with the original roof timbers and joists. “We were worried about loading too much weight onto the structure,” explains Stafford. “Originally there weren’t any ducts up there so we’ve gone for lightweight ductwork.” Although more expensive, the preinsulated Kingspan KoolDuct is only around 30% the weight of equivalent galvanised ductwork.

There was no space for conventional air-cooled plant and even if there had been there was the added problem of strict noise breakout limits.

The temperature of the main hall is controlled by both space thermostats and air quality sensors. As fresh air is drawn into the auditorium the extract fans work in sympathy with the supply air fan to provide a balanced air input/output.

The speed of the ahu serving the main hall varies depending on the mode of use. For rehearsals that only require the stage to be conditioned it is fixed at 20%. If the auditorium is included the speed is taken up to a minimum of 40%, which can then be varied depending on occupancy up to 60%, while for a full house the speed is increased to 100% to include the gallery.

The auditorium air extract also provides smoke control. These supplement the natural smoke sink created by the roof of the hall and, under its public license, allowed an additional 80 people in the audience above the natural threshold.

Five gas-fired sectional boilers, each of 100 kW, supply the building’s hot water and heating needs. As well as serving the two ahus these also feed the original, reconditioned, Haden cast iron radiators in many of the back of house areas that English Heritage insisted were retained.

Acoustics

Karl Brown of Absolute Audio carried out the acoustic design for Cadogan Hall. He explains that there were two main issues with the existing hall: first the concave ceiling shape, which focused sound into lobes along the halls length that were up to twice as loud as other areas; and second the general issue of the reverberation time just “not being right”.

Modelling of the space with an audience and seating in place showed that the reverberation time was “in the right area” as far as the high frequencies were concerned, all that was needed was to get the other frequencies in ratio with this.

To overcome the concave focusing effect of the semi barrelled ceiling Brown turned to a product he had developed almost 20 years earlier to tackle the design of a home recording studio. Based on the Helmholtz principle, the Resonant Adjustable Trap System (RATS) comprises tubes with a construction similar to that of a toilet roll tube – though with a specific number and type of paper elements wound on a forming tool that ensures dimensional stability. These can be adjusted internally to achieve the desired frequency, while allowing a uniform external look and fixing procedure.

For Cadogan Hall the RATS were scaled up to meet the sound diffusion and low frequency properties of the space, with just under 100 of the 4·3 m long, 100 mm diameter tubes being fitted to the underside of the ceiling. These do two jobs, firstly they provide a convex, sound dispersing surface and secondly they give a precise bass absorption down as far as 20 Hz. The issue of bass is particularly important says Brown. “Without controlling standing waves the bass in any room is all over the place timing wise. Louder than it should be at various points in the room and almost non-existent in other areas. Musically, timing, rhythm, and what we call ‘emotionality’ all hangs on the accuracy of bass.”

One other area of concern was the resonant activity of the raked concrete floor. This was monitored and checked regularly during construction. “We wanted this to not conduct vibration, and it doesn’t,” says Brown. “The reasoning here is that vibration in the floor would end up, via bone conduction, in your ear long before the sound reaches you through the air.” Making sure the construction was stable ensures that what the audience hears is sound waves in the air only and not vibrations in their feet, which can be distracting and ruin a performance.

Lighting

Performance lighting for the main hall needed to be flexible to accommodate the variety of events that would be held in the venue. A total of 18, 1200 W Clay Paky Stage Profile fittings are subtly installed in recessed cavities built into the ceiling of the hall. At £18 000 apiece these provide a full range of special features including colour filters and framing effects which can mimic actions such as dropping curtains or running water. These are operated by the control console mounted at balcony level at the rear of the hall, which also controls all the audio visual installations within the space.

Externally the hall is lit using a number of high output, led projector fittings containing 30 red, green and blue 1 W emitters. These self-contained fittings are used to illuminate the arches and tower and are capable of producing white light, subtle hues as well as primary and secondary colours.

Cadogan Hall opened its doors on June the 18 of this year in the opening concert of the 2004 Chelsea Festival, with a performance by Dame Kiri Te Kanawa and the newly resident Royal Philharmonic Orchestra. At a total cost of around £8 million it is debatable whether Cadogan Estates will see its money back on the scheme, but as well as ending 60 years of itinerancy for the RPO it has also reinvented a long neglected church building into a premier concert, rehearsal and arts venue.