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Tonwell Tower, a Grade II listed water tower in East Hertfordshire, was transformed into a multi-level holiday home by industrial designer Matt Grey, his wife Ali and their daughters. The conversion kept the tower’s concrete silhouette and turned its former water tank into a circular, open-plan living room.
What was Tonwell Tower before the conversion?
Built in 1964 to supply nearby Tonwell and Sacombe Park, the 23-metre (75-foot) tower held 230,000 litres (50,000 gallons) of water, according to Grand Designs Magazine’s 12 February 2026 feature. Its original tank was doughnut-shaped, supported by a central shaft and concrete stays. The tower’s distinctive form was not recreated for the home: it was the structure the family chose to adapt.
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How was the water tower converted into a home?
The self-build conversion took four years. Rather than fill the tower with conventional rooms, the project worked with its unusual geometry: three new floors were inserted below the old tank, between the central shaft and the outer concrete supports. Structural steel supports were added, openings were cut into the concrete, and two spiral staircases link the levels.
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Opening up the tank created a 60-square-metre circular living room, the home’s most striking interior. The tower now has more than 160 square metres of living space across its levels, according to Roca’s project case study. Grand Designs reports four bedrooms, four en-suite bathrooms and capacity for up to eight guests.
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New windows bring light into the concrete shell
Grand Designs reports that 40 triple-glazed windows were designed and specified by Grey for openings cut into the tower walls. Each weighs more than 120 kilograms. The glazing brings daylight and views into the previously enclosed structure while helping insulate the interior. Polished concrete floors with underfloor heating, a black granite and walnut kitchen, and restored Danish and British furniture complete the interiors.
What building systems does the tower use?
The feature reports a Daikin Altherma 3 high-temperature air-source heat pump for heating and hot water, alongside mechanical ventilation with heat recovery. Because the windows do not open, the ventilation system extracts stale air and supplies filtered fresh air while recovering heat. Smart lighting, automatic blinds, HomePod voice control, a projector and audio equipment are also reported as part of the home.
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These systems describe the building’s design, not proof of a particular energy outcome. The available sources do not provide measured energy use or quantified savings, so no reduction in bills or emissions can be established from the reported specifications alone.
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The project’s central design move was to reuse the existing concrete tower and make its original structure legible rather than disguise it. Grey told Grand Designs: “We were really committed to the sustainability of the project. That was really important to us. The concept of reuse has been core to the conversion.”
Roca, whose case study identifies the tower as Grade II listed, says the conversion complies with current environmental standards including BREEAM and reports environmental certifications including BREEAM and WELL standards. The case study does not provide certificate records or ratings, and the project sources do not quantify the environmental benefit of retaining the structure.
Roca’s supplier account also lists bathroom products supplied for the project: a Beyond Totem basin, Beyond wall-hung toilet, Beyond Surfex freestanding bath, W+W wall-hung toilet and basin, Insignia faucets and Tempo accessories. Roca describes the W+W as combining a basin and toilet and reusing basin water for flushing.
What is the main practical limitation?
The house relies on spiral stairs to connect its floors. The owners considered a lift but decided that fitting both a lift and stairs would take too much space. Grey told Grand Designs: “But that does mean, unfortunately, that this will never be an accessible property.” The striking circulation system is therefore a significant access constraint for anyone unable to use spiral stairs.
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Grand Designs reported in its 12 February 2026 feature that the tower was available to book on Airbnb as a holiday home for up to eight guests. Rental availability can change; the report establishes its status at publication, not whether dates are currently available.
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