Roving reporter, Michael Willoughby, talks to experts who provide hints and tips on maximising quality in the envelope.
It’s been a year since the Education Funding Agency (EFA) Large Contractor Framework was launched, and 18 months since ground-breaking took place on the first school to be built using the Priority School Building Programme (PSBP).
The PSBP is the coalition’s replacement for the last government’s Building Schools for the Future (BSF) programme. The £55 billion programme to rebuild or renew all schools was a sitting duck target for the then new education secretary, Michael Gove. The average cost of a new school was between £25-30 million, with some costing over £50 million. The media also focused on controversial projects such as Foster’s £31 million Bexley Business Academy, which was dogged with problems. Sure enough, Gove axed it in 2010.
Yet projected UK population growth and immigration is driving an average 12 per cent increase in schools places required across the UK (23 per cent in London) by 2024. Many buildings of the 1950s and 1960s are still in service, long after they should have been levelled. So the parsimonious government has had no choice but to continue a schools building programme. But there were rules.
Instead of overhauling every school in the land, the coalition prioritised the 261 schools most in need of repair. Costs were circumscribed at £1,113/sq m (versus apparently between £2,000 to £2,900/sq m under BSF). Baseline designs and areas based on pupil intake and number are specified in “baseline designs” and must be complete within six months. Schools were targeted to be 15 per cent smaller and 7 per cent cheaper.
The building envelope is likely to consume the largest cost of a school (19.3 per cent according to the US’ National Institute of Building Sciences). So, for this supplement, Architect’s Datafile sought out expert schools’ architects and suppliers to ask them what they had learnt building with the highly challenging EFA budget so far.
Holly Porter, founding director, Surface-to-Air Architects
Classy facades with simple prefabricated layouts
“We have been creating schools for 10 years, starting under BSF, the buildings were going bonkers. The envelopes were crazy. No expense was spared. Architects were having a great time! But clients weren’t necessarily getting value for money – it wasn’t being spent in the way it should have been. You had problems like the green wall at Paradise Park Children’s Centre in Islington, which could not be maintained and, so, died.
Our method remains to make use of techniques perfected in the office sector – to employ simple layouts with a high- quality finish.
Since the funding was cut, this has been a massive challenge. We have found that the only way to achieve the price point is to use a combination of standardised or prefabricated elements along with buying in bulk.
If you want quality at a low price you are not going to be using on-site building because you are relying on subcontractors. At least with factory finishes you have a chance of getting a high-quality spec.
The main players in prefabrication suitable for schools include Laing O’ Rourke, and its concrete system, cross-laminated timber (CLT) providers, such as B&K Structures, and whole-school solutions like Willmott Dixon’s Sunesis.
We work most often with Yorkon for the system and then employ high-quality finishes. Modular prefab can be highly adaptable if used properly.
Finishes don’t have to be boring, but they must be practical. We are particularly keen on Parklex, a timber-veneer cladding used on George Spicer Primary School in Enfield to create a grained effect. We employed colourful and syncopated Trespa rainscreen cladding for City Farm School, Barking and Dagenham and All Saints, Croydon.
We also use floor-to-ceiling glazing and bricks – although even the latter are becoming expensive.
At the moment, we are investigating Rodeca’s colourful translucent material used on the Laban. But today’s school clients can’t afford to be into innovation in materials – they will only approve something which has been used 10 times before, having learnt from the mistakes of the past.
All in all, I think schools – with the development of pre- fabrication techniques which have been used in Scandinavia for many years – are a very exciting sector to be in. It’s where progress is being made…”
Lee Fordham, Associate Architype Architects
Learning from Passivhaus for air tight envelopes
“Under BSF we built several schools better than Passivhaus (PH) standards, with air tightness levels below 0.3 air changes per hour at 50 Pascals pressure – the PH requirement being 0.6. We started at prices over £2,000 a sq m and managed to reduce costs to £1,800 then £1,700, and we were making further progress. But there is no way we could have got down to £1,100!
Nonetheless, we have managed to learn lessons from our work in order to maintain air tightness at around 3 with a target of 5, while keeping within the EFA funding requirements. That’s better than half Building Regulations’ requirements of 10. We maintain just one airtightness line through the build- ing – in other words, the insulation is continuous. It makes it easier to test and harder to destroy later on by, for example, punching a power point through it.
Furthermore, the insulation should wrap the building with the structure inside it unbroken – even if things don’t line up properly. For example, if you are designing a detail at parapet level you try to join the lines of insulation together externally. It’s not the usual, we know, but it helps to avoid thermal and cold bridging. Our approach is to use the minimal budget for robust details.
We would usually use prefabricated timber frame on our schools, insulated after installation. However, under the EFA we work on frameworks and the contractor generally goes with steel frame and poured concrete. We have tried to push them on timber frame, because environmentally we think it’s the best way to go, but they haven’t gone with it. We can only assume it is a cost issue.
Another place we had worked out a cunning timber solu- tion was reducing noise inside the schools by creating acoustic wall panels from off-the-shelf CNC and birch-based plywood. But with these costs, we have little choice but to use ceiling tiles to absorb sound.
For the MVHR we would have used before, the team goes with Breathing Buildings, a low-energy ventilation system that is proving popular among specifiers.
In summary, the EFA schools are certainly basic, and if you are – like us – trying to push the boundaries of PH, you will find experimenting in other sectors is the way to go!”
Mark Allen, head of technical for Saint Gobain
Choose technology for efficiency
“Software can be the key to not only building more efficient schools’ envelopes, but creating a better quality of life for its inhabitants.
DIAL is a German company that has created a free technology that helps designers create suitable artificial versus natural lighting designs in buildings. Using the tool, a school envelope is entered tagged to a particular global location and orientation and the programme will give lux values and relative visual simulations throughout using coloured squares for comparison.
The benefit of this is that you are able to accurately model the best place to put windows to maintain the correct lux values. This helps with energy conservation while providing adequate internal comfort along with correct temperatures to propagate maximum productivity in a learning environment. Many contemporary buildings are poorly designed from a lighting point of view because we use simple 1970 metrics like day-lighting factors. This can result in as-built performance, having in glare on the south side and it being too dark on the north, simply because the metric is too simple.
Better design will lead to efficiencies and savings and correct lux values by choosing the right glazing characteristics and window frames, light fittings – and paint colours!
The other benefit is that by remaining in control of glare, you can reduce the need for blinds, which subsequently then require artificial lighting. This uses excessive energy, but also produces unwanted heat, so you can control the comfort requirements of a building and reduce potential for overheat- ing and thereby remove the desire for mechanical cooling, together with related items which cost to run, maintain etc.
If we do need to design for overheating then we can use Rigidor boards on internal partitions or concrete, and, because we have optimised the solar gains versus internal lighting quality, many of the parameters that increase the overheating scenario are removed. We can therefore also optimise the requirement of heat sink materials to allow a flexibility building solution without the requirement for large thick con- crete structures.
With regard to thermal mass of the envelope, there seems to be a misunderstanding that thicker walls absorb more heat. But in fact it is only the first 100mm of dense materials that forms the heat sink and so thin layers of product can combat overheating without the excessive use of air-conditioning. These matters are not just about sustainability – but are about healthier schools that boost teachers’ well-being and student results.”
Off-the-shelf school envelopes
In light of the changing funding environment, several companies have created schools which can be ordered like an off-the-shelf product with a guaranteed price tag.
Sunesis from Willmott Dixon and Scape (a public- private partnership) delivers a whole-school envelope and interior walls for a defined cost over a fixed timescale. There are 12 different designs to choose from, divided into primary and secondary, and arranged by intake for primary schools and number of pupils for secondary. As an example, £2.8 million will buy you a two-form entry primary school including nursery school measuring 11,100 sq m built over 53-59 weeks, and 30 per cent cheaper than standard-build (although the schools are bricks and mortar).
However, Yorkon and Surface-to-Air are working on a modular product called the Configurator, which offers more flexibility based on the former (a Portakabin company’s) designs. School specifiers can choose the exact dimensions of internal areas, as well as finishes while being sure that they fit the EFA price tag.
Portakabin director, Kevin Jones, of his company’s schools, said:
“We don’t just make grey boxes anymore. They come in a multitude of sizes. We can specify air source heat pumps or mechanical cooling to fit the financial targets as well as a myriad of cladding options.”