Letters to lessons: how a sorting office became a school

Rowan Parnell, director at Architecture Initiative, was travelling in a car driven by a project manager from Northampton County Council. ‘We were driving past a large derelict building when he looked at me and said: “Do you reckon you could turn that into a school?”’ Parnell recalls. ‘I turned to him and said “Yes”.’ And so began Architecture Initiative's involvement with Northampton Academy.

That was five years ago.

The large derelict building had originally been a Royal Mail sorting office, but had been unoccupied for almost 15 years. Built in the brutalist style in the late 1970s, its dark, concrete interior was uncompromisingly functional, made up of a 6m high ground floor where mail vans were loaded; a 6m high first floor where the mail was sorted and franked; and a 3m high [ck] top floor, which had housed the management offices and a canteen. But it was the abandoned building’s location, on the perimeter of Northampton town centre, that made it interesting. It sat precisely where a new secondary school was required – hence the project manager’s question.

Now, Architecture Initiative's scheme has turned the forsaken structure into an inspiring centre of learning for 2,220 pupils. The building's mass remains largely unchanged, but a screen of perforated, polished metal now wraps around the front, concealing its brutalist lines and instead reflecting the academy's more sedate Victorian neighbours and a new entrance plaza.

It’s an impressive transformation, one that has required some clever interventions. ‘Originally the building was a big box 100m long and 60m wide, with very few windows,’ says Parnell. ‘The big issue was that there was no daylight entering the box and it was massively deep in plan, so if you were in the middle of the floor slab you could be 30m from an outside wall.’

Architecture Initiative's solution was to punch two rows of openings vertically down from the roof, through the second and first floor slabs to allow daylight penetrate deep into the interior and down to the ground floor.

Two giant circulation corridors now run the length of the interior, either side of the core teaching spaces. Above, the voids slice through the in situ concrete waffle-slab floor plates and roof flood these linear arteries with daylight, encouraging their use as break-out learning spaces and social areas.  Glass screens help maintain the visual links between these light wells and the double-height learning spaces positioned in the heart of the building.

It is an impressive transformation, one that has required some clever interventions. "Originally the building was a big box 100 metres long, 60 metres wide, with very few windows," says Parnell. "The big issue was that there was no daylight entering the box and it was massively deep plan, so if you're In the middle of the floor slab you can be 30m from an outside wall," he explains.

Architecture Initiative's solution was to punch two rows of openings vertically down from the roof, through the second and first floor slabs to allow daylight penetrate deep into the interior and down to the ground floor.

Work on the building's transformation started on site in August 2016. After the building had been stripped-back to its concrete structure, one of the first tasks was for a specialist concrete contractor to form the voids in the building's cast in-situ concrete waffle-slab floor plates.

Before any of the openings could be cut, a forest of props had to be installed to support the floors from the concrete ground slab.

Starting on the second floor slab and working down through the building, the contractor cut out a series of 7m x 9m holes. It then chipped back the concrete from the edges of the new openings by about 1m to expose the floor's steel reinforcement. Lengths of new reinforcement were then placed across the tops of the exposed rebar stubs and tied into place. Finally, the new assembly was encased in concrete to create an edge beam around each opening.

In addition, to maintain the integrity of the building's supporting structure, new beams have had to be installed across the void, spanning between structural columns.

Architecture Initiative's next structural intervention was to insert a mezzanine floor around the perimeter of the double-height ground and first floors. "In order to maximise the number of classrooms with access to natural light and the ability to be naturally ventilated we inserted a mezzanine floor along three sides of the building's perimeter so that we could double-stack the classrooms," explains Parnell.

The structure to support the mezzanine was formed by inserting steel beams between the outer wall and the first row of supporting columns. Unfortunately the building's 12.5m column spacing was not quite wide enough to accommodate a classroom in a single span, so the floor plate had to be extended 4m beyond the column to create the additional floor area and to form an access corridor. Rather than support the floor extension on additional columns, the projecting floor is suspended from the floor above.

A series of vertical windows cut into the perimeter walls allow light and fresh air into the perimeter classrooms. Most classrooms have three windows, one of which is fixed, one openable and one which features a louvred panel behind which is a ventilation unit. The windows are deliberately arranged so that they do not line up vertically in order to break up the uniformity of the huge facades. "The randomisation of windows completely changed the feel of the building while ensuring the right level of daylight for the classrooms," says Parnell.

In addition to inserting the mezzanine levels, the only major structural addition is a new sports hall on the building's roof. "The only bit of new-build is on top because that was the only place we could put the sports hall," Parnell says.

Work started on site in August 2016. After the building had been stripped back to its concrete structure, one of the first tasks was for a specialist concrete contractor to form the voids in its floor plates.

Before any of the openings could be cut, a forest of props had to be installed to support the floors from the concrete ground slab.

Starting on the second floor slab and working down through the building, the contractor cut out a series of 7m by 9m holes. It then chipped back the concrete from the edges of the new openings by about 1m to expose the floor's steel reinforcement. Lengths of new reinforcement were placed across the tops of the exposed rebar stubs and tied into place. Finally, the new assembly was encased in concrete to create an edge beam around each opening.

In addition, to maintain the integrity of the building's supporting structure, new beams have had to be installed across the void, spanning the space between its structural columns.

Architecture Initiative's next structural intervention was to insert a mezzanine floor around the perimeter of the double-height ground and first floors. ‘To maximise the number of classrooms with access to natural light and ventilation, we inserted a mezzanine floor along three sides of the building's perimeter so that we could double-stack the classrooms,’ explains Parnell.

 

The structure to support the mezzanine was formed by inserting steel beams between the outer wall and the first row of supporting columns. Unfortunately the 12.5m column spacing was not quite wide enough to accommodate a classroom in a single span, so the floor plate had to be extended 4m beyond the column to create the additional floor area and to form an access corridor. Rather than support the floor extension on additional columns, the projecting floor is suspended from the floor above.

A series of vertical windows cut into the perimeter walls allows light and fresh air into the perimeter classrooms. Most classrooms have three windows, one of which is fixed, one openable and one which features a louvred panel behind which is a ventilation unit. The windows are deliberately arranged so that they do not line up vertically in order to break up the uniformity of the huge facades. ‘The randomisation of windows completely changed the feel of the building while ensuring the right level of daylight for the classrooms,’ says Parnell.

In addition to inserting the mezzanine levels, the only major structural addition is a new sports hall on the building's roof. ‘The only bit of new build is on top because that was the only place we could put it,’ reports Parnell.

A sunken courtyard on the roof was the perfect size to house the sports hall. However, the roof's supporting structure had very little additional load bearing. To help reduce the loading before the new structure was added, the roof's covering of concrete paving slabs was removed, along with the upper layer of the concrete screed. The hall was then constructed using a lightweight structure of steel trusses mounted on steel columns.

The modest additions of the new sports hall and mezzanine floors emphasise just how much of the existing structure Architecture Initiative's scheme has successfully incorporated into its design for the new school. ‘One of the most sustainable things you can do is to reuse the structure,’ comments Parnell.

Where appropriate, additional insulation has had to be added to the existing building to meet the thermal requirements of the building regulations. ‘It’s about choosing the best, most cost effective elements to upgrade,’ says Parnell. ‘For example, we knew that we had to replace the leaky roof so putting a lot of insulation up there before water proofing it was an easy decision.’

As much as possible, the existing finish of the original building has been respected and reused, with a clear distinction created between old and new. The existing waffle-slab structure remains exposed, as do the new building mechanical and electrical services, and its standardised 0.9m-centred modular grid is used as a basis to inform and set out the spatial arrangement of the entire school.

Five years on from his drive past the derelict structure Parnell is clearly pleased with the building's transformation: ‘As someone who enjoys brutalist architecture its lovely to see the building has a new lease of life, because its previous life doing what it was designed to do was so short,’ he says.