Putting on a show

Anyone familiar with Manchester's Contact Theatre will recognise elements of the recently refurbished Poole arts centre. Now renamed Lighthouse, the oversized H-shaped chimney pots gracing the building's roofline are enough to hint that the team behind Manchester's dramatic theatre have had a hand in renewing the home of the Bournemouth Symphony Orchestra. Architect Short & Associates with engineer Max Fordham LLP have completed a major revamp of the building, transforming its exterior and replacing large parts of the original mechanical ventilation system with a new passive arrangement.

As the largest arts centre outside of London the £8.6 million refurbishment was a chance to put the building on the map. "The architecture wasn't terribly exciting, it looked like an office block, it never looked like an arts centre at all," says Bartholomew Stevens, partner with Max Fordham LLP. "It was very much the Contact Theatre which sold the architects to the client and part of the brief was they wanted some real wow factor."

The original arts centre was completed in the late 1970s by Poole Borough Council. Situated close to Poole's sea front, the building comprised a main concert hall with capacity for audiences of up to 2500, a 670 seat theatre, a 110 seat cinema as well as function rooms, a café and back of house and support areas. In terms of accommodation the scope of the refurbishment encompasses relocating the art gallery on the ground floor, remodelling the three existing foyers, bar and cafe, as well as the provision of a new 110 seat flexible performance auditoria (see figure 2). In addition to this, the roof has been given a major overhaul along with the facades, which alone required around £200 000 of investment replacing corroded cavity wall ties.

Funding for the scheme has come from the Arts Council Lottery Awards, the Borough of Poole and donations. However, the client didn't want to fall into the trap of spending money refurbishing the building only to find that they couldn't afford to run it later on and underlined the need to keep future operating costs and maintenance to a minimum. This was no doubt reinforced by the fact that the gas-fired absorption cooling system previously installed had been shut down 12 years ago largely because the running costs could no longer be afforded.

The project has been undertaken in three phases to enable the arts centre to meet performance and booking commitments, and as a result the refurbishment was procured on a two stage basis with the finalised contract being let on a PC/Works/1 with quantities basis.

Servicing strategy
Getting the best out of the building given the money available was always going to be a challenge. "It was such an enormous building," says Stevens. "Right at the beginning we decided that we would try and leave some areas almost entirely intact because as soon as you started doing anything you get sucked into a lot of work."

This meant work to the main concert hall and theatre were restricted to replacing the main air handling plant (which now incorporates run-around coils) new performance lights, sounds systems and remodelling the walls and ceiling of the theatre to alleviate the acoustic problems. Initially Fordhams planned to reverse the ventilation system in the concert hall. The Wessex Hall can be used in two modes, either with raked seating for 1400 people or in flat floor mode, with no seating, for audiences of up to 2500. To remove the seating the floor is lowered into a void below ground level, the seats are wheeled into storage and the floor returns to its original position. "At the moment air is supplied at high level and extracted at low level," explains Stevens. "But under here is an enormous concrete lined chamber which the floor lowers into. In the summer it is wonderfully cool so we wanted to utilise this and reverse the system to supply at low level. Unfortunately the money wasn't available."

External noise had also been an issue in both the concert hall and theatre due to the primary plant room being sandwiched between the two auditoria. The noise was largely created from the flues for the two mthw boilers – installed to serve the old absorption chillers – which ran up through the theatre auditorum and the edge of the fly towers. The decision to shut-down the cooling system, influenced partly by the noise it generated, meant boiler loads were now dramatically reduced. Despite this replacing the boilers with smaller units and rerouting the flues was not entirely straightforward. The plant room for the main ahus sit directly above the boiler room. The compromise was to install three new boilers; the flues for the lead and second boiler have been taken through the plant space avoiding the theatre altogether, the third flue passes through the theatre but this is expected to only fire-up occasionally.

Although cooling for the theatre and concert hall are not considered essential – the centre is shut throughout July and August – plans for a borehole cooling system were seriously explored at the design stage. The pipework and cooling batteries have been installed should the £70 000 needed to sink the borehole become available in the future.

Close control air conditioning has been installed in the relocated art gallery on the ground floor to meet the criteria set down by Re:source (Council of Museums, Archives and Libraries), with a minimum winter temperature of 21°C and a summer maximum of 24°C, both in the range of 40-55% rh. Similarly the location and arrangement of the cinema necessitated a comfort cooling system. This leaves the three remodelled foyers and the new flexible performance space (fps) which have adopted a natural ventilation strategy.

Natural ventilation
The centre's three foyers run along the front of the building on the ground, first and second floors and have been reconfigured to make more use of the space, particularly the height which was previously constricted by low false ceilings. Floor to ceiling heights vary with 4 m at ground level, 7 m on the first floor and 3·7 m on the second. In some respects the building's concrete frame structure lent itself to the strategy of natural ventilation, "It's quite a heavy weight structure so we tried to maximise on the use of that," recalls Mark Maidment of Fordhams. "But we were peppering the slabs with some large 2 m x 1 m holes for the extract stacks and this has meant some additional reinforcement is required in places."

The foyers are capable of holding a maximum of 2500 people at any one time but a peak of around 1500 is considered more realistic. A large bar area on the first floor where smoking is allowed means a design air flow rate of around 20 litres/s per person was considered. Stevens says no cfd modelling was carried out during the design phase. "We started off with some simple modelling to get a handle on the numbers and followed it up with Tas calculations." Air enters the foyers on the south (sea facing) facade. On the first and second floors it is brought in at low level and extracted at high level, but for the ground floor this wasn't possible, instead both incoming and extract is at high level. This wasn't considered a major problem as during intervals it was generally anticipated that people would gather at the first and second floor foyers creating less of a load on the ground floor.

Extract air from the three floors is treated separately to avoid any problems of heat contamination and under normal conditions exits through one of the three ventilation stacks. These are incorporated into a section of the building's south facade which comprises of a skin of Reglit glazing, a 1·5 m void and a second, curved Reglit wall (see figure 1). The void has been partitioned to create three air paths that are each connected to single H-pots, also manufactured from Reglit, mounted at roof level.

On the ground floor the façade is inset some 1·5 m from the rest of the building. Fresh air is introduced via high level openable windows through some attenuation and a heater battery into the space. "Spring and autumn days are often the worst case," says Stevens. Because this is south facing you might get a day when it's quite sunny and it gets very hot inside, but by late afternoon it might be 8°C outside and if you bring in air at that temperature people standing next to the inlets will feel cold. So we can heat it to get it to a minimum temperature." The exhaust path is through similar openings further along the facade, which are connected via a bulkhead to the extract stack.

On the first and second floor air is introduced via low level inlets beneath the existing windows. These are concealed in large window sills which incorporate finned tube heaters and a recirculation damper for the heating only mode. The extract air path for the first floor is similar to that of the ground, while the second floor makes use of an existing hole in the roof slab previously used for extract fans.

One of the drawbacks of the structure was the downstand beams supporting the slabs could potentially lead to 'reservoirs' of hot stale air forming at high level, particularly as this would be in contact with the slab hindering night time cooling. To prevent this horizontal holes, around 150 mm diameter, have been drilled through the beams as close to the slab as possible, effectively allowing any build up to drain away.

The designers were slightly concerned that the onshore/offshore breeze might act against them. "We could have the case where the wind was blowing straight at the façade, so it would be coming in without a problem but be prevented from going out of the stack in the same direction," says Stevens. To overcome this the main stairwell at the back of the foyers has been used to create a stack for the ground, first and second floors. In addition to this a redundant riser has been stripped out to serve a dead end section of the ground floor.

The flexible performance auditorium occupies the space vacated by the art gallery and has a finished floor level that is around 1 m below ground level. A large galvanised steel air intake adjacent to the south facing outer wall allows fresh air to enter via an acoustic closure controlled by a damper into the void behind the fixed seating. The air is heated by a series of finned heaters beneath the seats to guarantee a 15°C supply air temperature before entering the space through grilles set into the seating. The concrete roof slab has been exposed in the space and extract air exits via a series of holes drilled in the slab into an extract stack capped with a double H-pot arrangement. Compared to the foyers the noise rating for the flexible performance space was more stringent, the same NR25 as the concert hall, requiring greater sound attenuation particularly given the close proximity to a busy road.

As well as the acoustic splitters and motorised shut-off dampers, the stack also houses an extract fan, "This is for back up in case it should ever get very, very hot," says Maidment. "It shouldn't often need to run."

A Trend bems controls the naturally ventilated areas. This is linked to CO₂ and temperature sensors in the spaces and controls the actuators for the openable windows and the recirculation dampers to the foyers, as well as the inlet and outlet dampers in the flexible performance space.

Further works
In addition to the sloping site, the raked seating in the Wessex Hall complicates the building layout, requiring a number of half-landing levels to tie in exits/entrances particularly when the seating is in place. As part of the refurbishment new lifts have also been installed for the back stage entrances along with a new passenger lift on the front façade. This too is clad in Reglit glazing to tie in with the design of the ventilation stacks.

The external lighting scheme has been carried out by Peter Freeman. Cold cathode fittings have been fitted inside the ventilation stacks, while floodlights with coloured filters wash the Sto rendered walls. The building is brought alive at night with three animation programmes which link the speed at which the lights come on and off with the CO₂ levels within the building, as the building gets busier the animation moves faster.

The Lighthouse has now reopened its doors to the public and visitor numbers will testify if the refurbishment has succeeded in putting the building on the map. Commissioning of the controls is currently taking place. "The real test will come in the summer," says Stevens.