HAPA Architects restores grade II-listed home with sympathetic flint-faced extension

Tell us about the project

Black Tile House, in heart of the South Downs National Park, was a family home in need of restoration. Having been added to and amended in piecemeal fashion over many years, its plan had become muddled. Our client wanted to open up the interiors and bring in much needed light, and to add a new space that connected with the outside, where she could entertain and have a study. The extension needed to be modern but sympathetic to the existing grade II-listed house, and to its sensitive location.

Like the rear elevation of the house, it is faced in flint, but the material is reinterpreted in more contemporary form, with knapped corners instead of traditional brick quoins. Large sliding doors wrapped around one corner bring in a lot of light, along with rooflights in the flat roof. An oriel window makes a beautiful window seat, and frames views into the garden – which was also landscaped as part of the project, along with renovations to the garage and the pool.

How did the planning context influence the design?

The house is in a conservation area within the historic village of Firle. The Firle Estate owns most of the houses nearby, and has a covenant giving it the right of approval over any planning consent. So a traditional approach was required for the existing building, notably in the replacement of the black mathematical tiles on the front elevation, from which the house gets its name.

Getting consent for the much-needed extension was always going to be difficult. The material palette is shared with the existing house, but our main architectural principle was to make a clear distinction between what is new and what is old. The extension sympathetically and seamlessly connects with the traditional flintwork of the existing building, without overpowering or jarring with it. 

Explain the external treatment of the extension

In contemporary construction, flint is usually applied to the outer leaf of a conventional cavity wall. Here, we have an inner leaf of blockwork, a cavity filled with phenolic board insulation, and then a moulded panel – SureCav 50 – against which the flint is applied. Flint construction tends to be mortar-heavy, with potential for water ingress, but the panel ensures a clean and moisture-free cavity. It saves on space and cost too.

It’s easy to break flints when knapping them on two sides, which was necessary to produce the clean, sharp corners of the extension. I’ve had a go at flint knapping and obliterated the stone in seconds, so it was a joy to watch Flintman’s specialists perform their craft.

It was important that the structure didn’t flex, which might damage the flint work, so it is stiffened with steel near the cantilevered overhang and around the oriel window.

How have the interiors have been designed?

We worked with Louise Wingate-Saul on the specification of products and finishes. As a team we were keen to retain the historic qualities of the house. Renovations that took place before our clients’ occupation were not very sympathetic, so we looked at older parts of the building as reference points. 

What was your approach to sustainability? 

The extension has been built to very high thermal standards, reaching U-values that surpass the 2022 regulations. Walls are 0.15 W/m²K, the floor is 0.13, and the roof 0.12.

It also has underfloor heating and LED lighting. The large areas of glazing are positioned to allow for solar gain in the morning, but are overshadowed at mid-day in summer. That helps to passively heat the room without overheating.

It can be hard to add insulation to listed buildings, but we were able to introduce additional quilt insulation to the roofs of the existing house.  

What were the biggest challenges, and how did you overcome them?

Working on a grade II-listed building certainly brings challenges. Special care and attention was taken throughout; through careful research we sourced coving and architraves to match the originals, for example.

Renewal and re-attachment of the mathematical tiles on the front elevation of the existing house was a true labour of love. They had slipped and were generally in a bad state of repair.

Tiles were carefully removed and set aside for relaying once the battens and wall had been rectified. The next task was to find replacements to match the broken or damaged tiles; although the original manufacturer is no longer around, we were able to find one who used an identical glaze to make new tiles.

We consulted with the council’s conservation team on laying patterns, and mixed new and original tiles across the facade, but with newer tiles towards the top, further away from viewers on the ground. The result is excellent, but the whole process was research-intensive and time-consuming. Approaching a similar situation in future, we’d allocate more time to it at an earlier stage in the project.

Another tricky aspect was building in a quiet village during Covid lockdowns, which caused some local disquiet. We did what we could to ease the situation, for example by installing a sound-proof shed in the garden where materials could be cut.

What is your favourite moment in the project?

Working with master craftsmen was a special process, and the work was exceptional. With any trade that takes a lot of thinking and a lot of hands-on ‘feel’, you get the best results by watching and talking to people, not just issuing instructions.  

Among our highlights is the oriel window facing the garden, which was carefully detailed to be ultra-sleek when viewed from the outside, while being warm and cosy inside.

Externally it is clad in zinc and has an infinity edge to the glazing, hiding the insulation and build-up of the frame. Internally it is a reading nook, lined in oak to complement the floors, and presents a picture window framing views of some of the wonderful plants and features of the garden. Listed buildings often have relatively small windows, but here we have opened up a section of the house to create light and space, while retaining its original character.

Stuart Paine is a director at HAPA Architects

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IN NUMBERS

Total contract cost: £750,000 (whole house alterations, extension, garage, garden, pool and landscaping)
Gross internal floor area: 303m² 
Cost per m²: £2475