Natural ventilation on the 12th floor: RSHP's new towers for LSE

The Centre Building opened its doors to students at the London School of Economics and Political Science (LSE) for the first time this autumn. Designed by Rogers Stirk Harbour + Partners (RSHP), the 16,000m² scheme consists of two linked steel-framed blocks, of six and 13 storeys. The lower floors house a café, lecture theatres, a basement auditorium and seminar rooms, while the upper floors are home to five academic departments. The blocks look out over a new public square, designed by RSHP to improve connectivity and to give the congested Holborn campus a much needed focus.

RSHP won the RIBA competition to design the £78 million scheme in 2013 with a proposal that set out to encourage academic collaboration and which embraced sustainability in response to the LSE’s requirement for a BREEAM Outstanding building.

Collaboration is encouraged by the Academic Stair, a giant staircase that zig-zags up the main block from level three to 12. Viewed from the square, it appears in the facade as a series of stepped, double-height windows. It is designed to encourage serendipitous dialogue between departments while providing informal places for staff and students to interact. Two further staircases act as circulation and meeting spaces: one ascends from the entrance through the atrium separating the two blocks; the other, which incorporates terraced seating, descends to the main lecture theatre hidden beneath the new square.

To meet the brief’s sustainability requirements, RSHP designed the 10 departmental floors served by the zig-zag stair to be naturally ventilated. It is an ambitious solution for such a congested central London site; one that necessitated RSHP working closely with environmental engineer ChapmanBDSP to develop a holistic solution coupled to a carefully engineered building envelope. ‘The natural ventilation has got to work, there is no plan B; there isn’t even any riser space to add cooling in the future,’ says Tracy Meller, the RSHP partner who led the project.

The natural ventilation design was driven primarily by the need to minimise overheating rather than to meet the fresh air requirements of the occupants. Floor plates are deliberately shallow to encourage the cross-flow of fresh air. ‘The majority of the floors are just 13.5m wide,’ she says.

Thermal mass has been added to the exposed steel-frame through the use of ‘cheap-as-chips’ precast concrete plank floors, which Meller says are ‘more usually used for car parks than academic buildings’. The concrete is exposed as the soffit of the floor below; its thermal mass helps moderate temperatures by absorbing heat during the day.

Solar gain is carefully controlled. The main facades face east and west; lower floors are shaded by the surrounding buildings but the upper floors are exposed to uninterrupted solar radiation. These facades incorporate vertical aluminium fins of various depths to shade the glazing from the oblique sunlight. Parametric modelling by ChapmanBDSP ensured the fins are slimmer on the more sheltered lower floors to maximise daylight. ‘We worked hard to get a system that worked; lower down the building is overshadowed but as you go up the building the louvres get deeper to combat solar gains,’ explains Meller.

These fins are a subtle grey when viewed from Houghton Street, home to some of the LSE’s older buildings, whereas viewed from the square they are accented in bright yellow. ‘We wanted the building to appear more playful when seen from the square,’ she says.

The success of the natural ventilation depends on there being open plan spaces on each side of the floor plate to facilitate air movement across it. Most academic floors are a carefully controlled mix of open plan and cellular accommodation. ‘We have to keep at least three open plan bays, one on one side of the building and two on the other side,’ says Meller. 

 

As might be expected, there was a big debate on the amount of open plan versus cellular. ‘The estates department wanted most spaces to be open plan because it’s a much better use of space, whereas the majority of academics wanted their own offices,’ she says. RSHP’s approach was to create a 3m wide facade module that works regardless of whether a space is open or compartmented, adding future flexibility to the scheme while cleverly shifting the burden of allocating floor spaces to the LSE estates team.

Each module has a large glazed panel to maximise daylight in the space. Above the glazing is a smaller actuator controlled window that is opened and closed by the building management system to moderate the ventilation rate throughout the day and to enable the floors to be purged of residual heat overnight to recharge the thermal mass.

The module also incorporates what Meller describes as a ‘windoor’ – a large, hinged opaque panel adjacent to the glazing that can be opened inwards by the occupants to boost ventilation. When the windoor is open, the BMS turns the heating off. ‘It’s a managed ventilation system that gives users control,’ she explains.

In contrast to the naturally ventilated upper floors, mechanical ventilation supplies fresh air and cooling to the lower floors. The plant room at basement level 1 houses most of the MEP plant including a biofuel-fired combustion CHP engine, which burns waste from the pharmaceutical and cosmetics industries to provide the building’s heat and power. The engineers claim its carbon emissions are significantly lower than they would be for a gas CHP. Other sustainability features include  rainwater attenuation and harvesting tanks and photovoltaic panels on the roof. 

 

The project was constructed by Mace under a design and build contract. In addition to the challenges of such a constrained, central London site, the team also had to deal with additional costs resulting from the fall in the value of sterling after the Brexit referendum. For example, the cost of the aluminium cladding package, which was being fabricated in Germany, increased by £1.5 million. ‘We suffered quite extreme value engineering,’ says Meller. ‘The drop in the value of the pound as a result of the Brexit referendum meant the cost of many packages went up overnight; since the budget was fixed, we had to find the money by value engineering the scheme – we ended up doing four rounds of VE.’

Despite this obviously painful exercise, the team deserves enormous credit for delivering such an impressive scheme that meets the LSE’s brief for encouraging interdepartmental collaboration and sustainability. What’s more, the building is the first on the campus to achieve a BREEAM Outstanding rating. 

---

IN NUMBERS
£78m
total cost
16,000m²
gifa
13
storeys 
3m
width of facade module