Tonbridge School – Building Conservation and Modernisation

Conservation refurbishment (Grade II listed) and modernisation

Converting the school’s Cawthorne Lecture Theatre into staff facility, with conservation of heritage features

Project Details


Tonbridge, Kent (within conservation area)


Tonbridge School

Project Manager



ADP Architecture

Programme Period

60 weeks

Contract Value

This transformational project not only showcases exceptional craftsmanship but protects the cultural and architectural legacy of the Cawthorn Building, while faithfully adhering to historical accuracy in the restoration work. It also keeps alive - and passes on to future generations of construction professionals – the skills of specialist heritage tradespeople, many of whom are local to the area.

Baxall were engaged by long-term client Tonbridge School on a JCT Standard Building Contract to convert its Grade II-listed Cawthorn Building – originally a chapel built in the 1850s – into a staff common room. Having been converted into a lecture theatre in the early 1990s, the building needed extensive and sympathetic conservation and repair works (both exterior and interior) to retain ecclesiastical features and modernise the services with facilities including showers, separate WCs and a café area.

All works were undertaken within a live/occupied school environment in the north of Tonbridge’s Conservation Area. Early engagement was critical due to the Conservation Officer’s heavy involvement in this project. Baxall’s team started on site in October 2022 by carefully removing the three existing mezzanine floors; internal strip out was complete by Christmas then the team had eight weeks of pre-commencement conditions including regular meetings with the Heritage Officer. A free-standing external scaffolding was erected around the entire building to facilitate cleaning of the sandstone using a high-pressure, non-abrasive 150 degree C steam system to carefully remove the build-up of moss, algae and soot.

Perhaps the most challenging element was the conservation of the fragile Gothic-style tracery windows, undertaken by specialist heritage glass sub-contractor, Easthope Studios. Using an internal scaffold to prop up the traceries, the windows were carefully removed by cutting away the pointing on the exterior face to expose the glazing grooves.

Bespoke stretchers were used to painstakingly remove the stained glass and lead lights – in particular from the west and east elevations where some of the mortar and mullions had fractured, pulling apart the stained glass in situ – and transport the fragments in custom-designed boxes to the studio in Folkestone. With the original glass in the workshop for 16 weeks, the team used polycarbonate sheets to keep out the weather and wildlife.

Once in the studio, all pieces were carefully photographed as part of the conservation record. Graphite pencil rubbings revealed the lead matrix and individual panes of glass from which to rebuild a detailed image of the original artwork. After cleaning and repairing (while salvaging as much of the original glass as possible), the panes were kiln-fired ready for the re-leading process using gas soldering and tallow. Weatherproof cement was applied between the glass and lead before final cleaning, polishing and reattaching the tie wires. The glazing was then fixed in situ with lime mortar.

Peelaway 1 was used to remove existing paint from the stonework and clean the bosses and 32 columns, as well as carefully restoring to its former glory the ornate red Devonshire marble, which had been painted over since the 1990s.

The services in the loft were stripped out and replaced with a fire alarm system, serviceable from the ground floor. A specialist joinery company repaired the missing and damaged mouldings by making new mouldings to match, including the hand-carved tulipwood nature motifs (which can also be found in London’s Houses of Parliament, potentially suggesting the same original artisan).

In addition to installing new electrical and water services the team connected the foul drainage (located on the other side of the building, across manicured lawns) to the local sewer. Installing the showers and WCs under the mezzanine floor meant bringing in new drainage since the existing building had none. At 1.2m depth, the walls measured 1.5m thick, which meant diamond drilling through to eradicate the need for any temporary works before hand digging the steelwork pad foundations. The new mezzanine steel frame and staircase were installed and then concreted to form the spaces below the mezzanine floor for the plant room, changing rooms, shower and WCs.

While stripping up the existing floor boards to install the new services, the team found they needed to replace around 90% of the floor plates and joists, which had rotted away. It was at this point the team discovered the building’s original flooring made from stone substrate with clay tiles running the entire length of the chapel. At the client’s request, this was transformed into a feature and covered with a triple glazed, 2m2 non-slip glass panel complete with LED lighting in front of the bar area. Engineered oak was laid throughout the ground floor and bonded by a moisture-resistant ply substrate.

Baxall’s in-house decorating team carried out all the internal paint stripping and stone cleaning, painstakingly hand-cleaning the internal stone reveals to remove dirt and dust, and replastering the entire interior in lime render. Meanwhile heritage sub-contractors replaced 70m2 of cementitious pointing on the exterior with lime mortar.

Securing the eight, 3m-diameter halo lights 6.5m high in the arched roof proved to be technically demanding and required tower access. Another challenge was how to install the secondary glazing panels (each weighing 60kg) without using mobile access equipment to prevent damage to the flooring. To overcome this, the team laid temporary mats and used a robot vacuum suction system to lift up and accurately install the panels 2.5m high to 12 windows on the north and south elevations.

Accommodating the correct power supply to the re-purposed building meant upgrading the school’s power station, which Baxall fully managed and coordinated with UKPN. Laying the necessary cables required 160m of trenching to be dug through manicured lawns and gardens (the entire school is a conservation area and every tree is classified as protected), hence Baxall worked closely with the local Tree Officer to carefully observe root protection zones.

Baxall is highly adept at working in live/occupied educational environments where the holiday periods – especially the summers – provide opportunities to carry out disruptive programme elements. Tonbridge School however maintains a year-round busy events programme with regular performances at the on-site (public) EM Forster Theatre, sports festivals and shows, with weekly weddings throughout the summer.

The delivery team needed to accelerate (at very short notice) the external works programme by three weeks to accommodate a late-booked wedding. This meant pulling out all the stops to relay turf and tarmac by the Friday night in time for the school grounds to once again look pristine ready for the wedding on Saturday. Regular and open communication between the school and Baxall was therefore essential, as was the team’s accurate weekly forecasting of upcoming site activities.

Accommodating busy exam periods was another challenge which Baxall successfully overcame by holding weekly operational meetings with the school’s H&S Officer and Marshal to fully understand their daily operational requirements. For example, all site operatives maintained strict quiet periods in the summer term to accommodate language exams taking place adjacent to the Cawthorn Building works.

The building’s location on a landlocked site with multiple shared access points (and within an occupied school) in busy Tonbridge meant logistics and safety management were paramount throughout the project. The site perimeter was bordered on three sides by public footpaths, Tonbridge High Street and in close proximity to private houses, commercial facilities and EM Forster Theatre. Baxall worked closely and collaboratively with the school management from the outset to develop robust logistics strategies enabling the school to run uninterrupted in parallel to the works, while mitigating disruption to the general public.

Baxall proudly handed over the building two weeks ahead of schedule ready for the school to complete fit out ahead of the start of their new term in January 2024.

This transformational project not only showcases exceptional craftsmanship but protects the cultural and architectural legacy of the Cawthorn Building, while faithfully adhering to historical accuracy in the restoration work. It also keeps alive – and passes on to future generations of construction professionals – the skills of specialist heritage tradespeople, many of whom are local to the area.

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