Scallop House: A Rammed Earth Effect Exterior in Stoke Newington

At the end of a narrow garden in Stoke Newington, a new extension is taking shape against the back of a Victorian terrace. Its garden elevation curves: a softly scalloped parapet, rounded columns and deep hoods over each opening. Above and around it, the original house is built in yellow London stock brick, with gauged arches over white sash windows.

For the new walls, we have chosen a rammed earth effect exterior finish. It is a hand-applied, lime-based render laid in horizontal bands of sandy colour, so the surface reads like layers of earth. As the light moves across the garden through the day, the bands and their texture will shift, sitting in quiet conversation with the brick above.

Scallop House is now on site, and we are still testing colours with physical samples before the finish is applied. For the wider project story, read Scallop House: From Concept to Developed Design.

Design visualisation of Scallop House’s garden elevation, with a scalloped parapet and layered rammed earth effect render beneath the Victorian brickwork.

Why a rammed earth effect suits Scallop House

The extension is defined by its form. The scalloped parapet, curved columns and deep opening hoods give the garden elevation a sculptural, carved quality, and the finish needed to support that.

Earlier proposals showed these forms in a plain, warm lime render, first in a pink-terracotta tone and later in buff. As the design developed, we wanted a surface with more depth: one that would follow every curve, catch the light differently through the day and make the extension feel rooted in the garden rather than placed in it. A layered finish does that.

Our clients liked the first layered sample we tested, and the rammed earth effect is now the preferred finish.

Rammed earth, clay plaster and lime render

The words are often used loosely, so it helps to separate three materials.

• Structural rammed earth is a wall built by compacting damp soil in layers inside formwork. The wall carries load and has substantial mass.
• Clay plaster is an interior finish made from clay, sand and natural pigments, applied over a wall rather than forming it.
• A rammed earth effect exterior finish is a lime render applied in coloured layers to recreate the look of rammed earth on an outside wall.

Scallop House uses the third outside. The finish recreates the appearance of rammed earth. It does not provide its structural properties or substantial thermal mass.

Inside, we have specified clay plaster to the walls and Bauwerk limewash in the kitchen.

Can clay plaster be used outside?

Generally, not on an exposed external wall. Unfired clay softens when it gets wet. That makes it easy to repair indoors, but leaves it vulnerable to driving rain, which is why most clay plasters are made for interiors.

Indoors, clay plaster is valued because it can help moderate humidity, contains no synthetic binders and can be re-wetted and repaired by hand. Those are qualities of clay.

For outside walls, manufacturers such as Clayworks produce separate lime-based exterior finishes, formulated for walls exposed to the weather. They can be colour-matched to clay plasters inside or built up in bands for a rammed earth effect. The exterior system has its own technical documentation; performance claims and certifications should be checked against the specified product.

Why not build in structural rammed earth?

Structural rammed earth, including insulated rammed earth, can be an excellent choice on the right project. It suits sites with room for formwork and compaction, appropriate foundations, time for the walls to dry and, ideally, suitable soil or aggregate close at hand.

Scallop House is a Victorian terrace extension in Stoke Newington, on a narrow plot close to neighbouring boundaries with limited access. Every centimetre of wall thickness comes out of the room inside or the garden outside. Here, an insulated wall with a thin, hand-applied finish meets our fabric-first performance targets while keeping the footprint tight and the construction manageable on a constrained site.

How the wall behind the finish works

A wall does several jobs at once, and they are easy to blur together.

• Insulation slows the transfer of heat through the wall.
• Airtightness is a continuous layer that stops air leaking through gaps, which matters for energy use and for keeping warm, moist indoor air out of the construction.
• Vapour permeability describes how readily water vapour passes through a material. Whether a wall can actually dry depends on the complete build-up, not on any one layer.
• Rain protection is the outer layer's job of shedding liquid water.
• Drainage and ventilation give any water that gets past the outer layer a route to drain away, with moving air to help it dry.

Breathability alone does not prevent moisture problems. A durable wall depends on all of these working together, and on careful detailing at junctions, openings, copings and the base.

At Scallop House, following Clayworks' advice, our proposed detail treats the facade as a rainscreen. The render is a 16mm build-up, applied to two layers of cementitious board that form the scalloped curves. Behind the boards, a drained and ventilated cavity separates them from the insulated wall. This is our design response to a lightweight, curved extension, not a requirement for every natural finish.

Testing colour with physical samples

Published examples of rammed earth effect finishes range from warm pink and terracotta bands to sandy neutrals and darker, almost chocolate layers. Each would change the character of the extension, which is why photographs alone are not enough.

Our first physical sample was a board in Clayworks' Coarse Rustic exterior finish, alternating two colours: BRO-06, a warm sandy brown, and TSN-06, a softer, paler tone. In the hand, the coarse aggregate gives a gritty texture, and the soft, undulating edges between the layered bands read convincingly as strata. This combination is now proposed for the main body of the walls.

The next question is emphasis. We think three elements need a slightly deeper tone:

• The base, where the walls meet the patio
• The hoods framing each opening
• The top of the scalloped parapet

A darker base anchors the building to the ground. Darker hoods suggest thickness and deepen the shadow around each opening. A darker parapet edge draws out the scalloped profile against the sky. The base also sits in the splash zone, where a deeper tone will be more forgiving as the finish weathers.

We have requested three further samples, BRO-02, BRO-03 and BRO-04, to test against the main panel. Exterior samples can take up to two weeks to make, so this is built into the programme.

Sitting alongside Victorian yellow stock brick

The finish does not imitate the brick, and the extension is clearly new. But the two share a visual language: warm yellows and browns, a hand-made texture and natural variation across the surface.

We will review the samples outdoors, beside the existing brick, in morning and evening light. A tone that looks right on a desk can read very differently next to a weathered Victorian wall.

Front and reverse of the Clayworks exterior finish sample, testing sandy tones and layered texture for Scallop House.

Considering a rammed earth effect exterior finish?

If this kind of finish appeals for your own extension or retrofit, these are the practical points we would discuss early.

• Exposure. Consider orientation, exposure to wind-driven rain and how much shelter the design gives. Horizontal ledges, copings, sills and the base need the most care.
• Specification. Treat the finish as part of a system: substrate, render coats and the wall behind. For a bespoke finish, ask the manufacturer to confirm the build-up and substrate in writing.
• Samples. Ask for samples in the exact texture and colours proposed, and judge them outside next to your existing materials.
• Specialist application. Custom finishes depend on the applicator's skill. Clayworks require their custom finishes to be installed by an approved applicator, so check availability and allow for this in the contractor's programme.
• Weathering. A textured mineral finish will change over time. Well-designed drips, copings and overhangs decide whether it weathers evenly or stains.
• Maintenance and repair. Plan for periodic inspection as part of routine facade maintenance. Localised repairs are possible, but matching a banded, multi-colour surface is more demanding than patching a single colour, so keep a record of the finish and colour codes used. Clayworks offer a 10-year manufacturer's warranty on their exterior finishes, subject to correct detailing, application and maintenance.

What affects the cost

A useful figure depends on the specific design, but the main cost drivers are predictable:

• The area of finish and the scaffolding or access needed
• The complexity of the form, as curves, scallops, reveals and hoods take longer than flat walls
• The number of colours and bands, and whether custom colours are needed
• The wall build-up behind, including substrate boards and any ventilated cavity
• Specialist application by an approved applicator
• Sampling and lead times
• Detailing at the base, openings and parapet, including flashings, copings and drips

Involving your architect, contractor and applicator early is the best route to a reliable price.

What happens next

When the new samples arrive, we will test them against the main panel and the existing brick, then confirm the final palette with our clients and the contractor ahead of application. We will share photographs once the extension is complete.

Planning an extension or retrofit?

If you are considering an extension or retrofit and would like to explore lime, clay or other natural finishes, we would be glad to talk it through. Please do get in touch.

→ Email us at architects@risedesignstudio.co.uk
→ Or call the studio on 020 3947 5886

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