A learning experience

Major extension to Addey and Stanhope School, London SE14 (design started in February 2000, building occupied May 2003)

The new building for Addey and Stanhope School employs novel strategies to overcome the inherent difficulty in providing new educational facilities to current standards on a tight urban site right next to the A2, a major route out of London.

The design philosophy was to rely on low energy, passive measures, to both ventilate and, where possible, heat the building rather than complex high maintenance plant that would be difficult to maintain and costly to run. The classrooms are orientated to the east and west to ensure adequate levels of daylight while avoiding excessive solar gain. Roof lights provide daylight to the heart of this deep-plan building. The proximity of noise and pollution from heavy traffic suggested the need for a sealed building envelope to create spaces suitable for teaching. To provide the necessary quantities of fresh air – at that time specified as 8 l per person per second – the architect worked closely with Monodraught to develop an attenuated wind-catcher to naturally ventilate all teaching spaces while filtering out excess traffic noise and pollution.

A large window wall to the southern stair allows this “buffer” circulation area to be heated by solar gain. In summer windows can be opened to cool this space. Construction is generally heavy and highly insulated; the inner leaf of dense concrete blocks counters the external noise while good insulation ensures heat from the highly efficient condensing boilers is retained.

Lessons learned

Condensing boilers proved problematic in practice – especially given the low velocity of water flow and the large quantities of vapour produced from the flues – and took a lot of commissioning before they functioned fully as designed.

The under floor heating pipes to the gymnasium were punctured during installation resulting in disruption for the school and a large insurance claim to cover the drying out of the floor screed and full replacement of the sprung timber floor.

The external blinds to the large east-facing windows were omitted during a difficult construction phase. Subsequent overheating during the heatwave of 2003, ensured this omission together with fixed louvres to the shallow pitched roof lights, was rectified. Comfort levels in the affected spaces were much improved this summer following the installation, especially given the regularity of exceptionally hot conditions.

Brunel University is carrying out post-occupancy evaluation of temperature and air quality levels this summer to assess the effectiveness of the Monodraught wind-catcher design and controls.

The building is featured as a case study in Building Bulletin 93, demonstrating how the measures employed (high-performance double-glazed windows, solid dense block walls, attenuation to the wind-catchers) delivered on the design parameters.

Early use of thermographic imaging of the building illustrates the need for further improvements in the design of the external envelope to reduce cold bridging.

The Bishops Justus Secondary School, Bromley, Kent (scheme design started in May 2003, building occupied September 2005)

An alternative strategy for natural ventilation was used on the new-build Bishop Justus secondary school in Bromley. The Passivent system uses electrically operated louvres to the external wall to provide supply air, preheated by perimeter radiators in the winter months, and extracted at high level again through BMS-controlled louvres. In the classroom block, ducts from four rooms are combined in a single chimney relying on the stack effect to exhaust air. In acoustically sensitive locations, such as music and drama rooms, wind-catchers have been employed to draw the air from high level, away from sources of noise, to provide fresh air and exhaust through the same terminal, which is divided into four quadrants internally.

Other static systems include overhanging eaves and banked external louvres to the south-facing elevations to reduce solar gain and reduce glare. However, given the now universal adoption of digital projectors and interactive white-board technology in new classrooms, internal blinds are still required.

The widespread use of sedum roofs improves the level of sound insulation and the interception times for rainwater run-off and provides a beneficial micro-climate that is attractive to wildlife. The significant cost of providing attenuation tanks to reduce the discharge into the now overstretched sewerage infrastructure led to the adoption of a sustainable urban drainage system. All rain and surface water run-off is channelled into a series of holding and filtration ponds prior to their discharge into a nearby river.

Alternative energy sources were considered including biomass boilers and solar power, but there was no allowance in the capital budget.

Lessons learned

The relative positioning of roof terminals has led to unwanted noise in strong winds, known as the Aeolian harp effect. Increasingly designers must consider whether to embark on more sophisticated early modelling of possible wind noise.

Early education of the building users is essential to ensure the optimal performance of the natural ventilation system that has been adopted – as in the absence of ever more sophisticated controls (eg air quality, temperature and wind speed), it is the human response that dictates the outcomes.

Major extension to New Woodlands School, Downham, Bromley (design started in February 2005, due for occupation in May 2007)

The proposed large extension to New Woodlands, a special school catering for pupils with behavioural, emotional and social difficulties, further develops design ideas pioneered on the previous projects while absorbing a number of additional requirements imposed by having to achieve a “very good” BREEAM rating. Full compliance with the new Part M (disabled access) and the unexpected impact of new disproportionate collapse regulations in the new Part A (structure) approved documents also affected the adopted design.

A significant projection of the roof to the south-facing elevations, combined with banked horizontal louvres, allows extensive glazing to the new multi-purpose hall and also the administration offices in the single-storey link block, while providing a non-institutional image to the public face of the building. A distinctive appearance is important as many of the pupils who will attend will have previous negative experience of education, often having being excluded from past schools.

The two-storey classroom block faces west to the outdoor play areas, with vertical energy screens to reduce solar gain. Light shafts allow the ground floor classrooms to be deeper in plan and allow for cross ventilation that utilises the stack effect. Smaller group spaces are positioned in their optimum location between pairs of classrooms. Openable rooflights at first floor level allow these rooms to benefit from natural cross ventilation from the prevailing westerly winds. The section also allows natural light into the generously proportioned main circulation corridor, deliberately wide to minimise the possibility of conflict between pupils.

The resulting deep plan, in excess of 18 m, provides benefits in respect of heat retention, especially when combined with a highly insulated building envelope and “green” palette of materials to give an improved BREEAM score.

Earth ducts were specified to provide comfort cooling to the two spaces that were most likely to overheat, namely the hall and the ICT room. Because of cost constraints
the ducts only extend to the void below the suspended ground floor slab rather than extended underground to a remotely located terminal.

Lessons learned

The impact of both Part A and Part M resulted in additional costs not previously associated with perceived efficiencies of a two-storey building. In this case, due to the limited available site area common to most schools in urban settings, a multistorey solution was required to maintain minimum areas for outdoor play.

BREEAM encourages designers to adopt holistic environmental strategies, including improved provision for cyclists, additional refuse storage space to encourage recycling, conservation of existing wildlife on the site and the adoption of a “green specification”, occasionally tempered by future maintenance costs – acrylic render on insulation, linoleum floors, aluminium framed windows – rather than better rated timber.

Key documents

Building Regulations

• Part A3 Structure Disproportionate Collapse (published 2004)
  
• Part E Resistance to the Passage of Sound (effective July 2004)
  
• Part F1 Means of Ventilation (published 2006)
  
• Part L2A Conservation of Fuel and Power (new build – non-domestic) (effective April 2006)
  
• Part L2B Conservation of Fuel and Power (existing – non-domestic) (effective April 2006)

Other regulations

• The Workplace (Health, Safety and Welfare)Regulations (effective 1992)
  
• The Education (School Premises) Regulations (published 1999)

Building Bulletins

• BB 79 Passive Solar Schools A Design Guide (published 1994)
  
• BB 87 2nd Edition: Guidelines for Environmental Design in Schools (published May 2003)
  
• BB 90 Lighting Design for Schools (published 1999)
  
• BB 93 Acoustic Design of Schools impact on ventilation strategy (published 2003)
  
• BB 98 Briefing Framework for Secondary School Projects (published 2004)
  
• BB 101 Ventilation of School Buildings (published May 2005)

EAM

• BB 83 Schools Environmental Assessment Method [SEAM] (published May 1996)

BREEAM Schools (launched January 2005)

The following must achieve a very good rating

• primary school projects costing £500,000 or more
  
• secondary school projects costing £2m or more
  
• all projects involving remodelling or refurbishment of more than 10% of the total gross internal floor area of a school.