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KH House by Delvendahl Martin Architects


In this extension to a Grade II-listed farmhouse Delvendahl Martin has used local natural materials, such as flint and oak, at the heart of its design. Photography by Tim Crocker

KH House is a residential project involving the extension of an existing Grade II-listed Berkshire farmhouse in an Area of Outstanding Natural Beauty. The client’s brief was to extend the farmhouse and create a living and dining space from which views of the river and landscape could be enjoyed. 

Delvendahl Martin’s design of the extension emphasises the relationship with the surrounding landscape as well as with the existing building, creating a contemporary reinterpretation of a local vernacular. The introduction of an asymmetrically vaulted roof maximises views towards the river to the south while reducing the visual impact of the building on the approach from the north. The roof form makes reference to the agricultural building typology found in the immediate farm setting and in the wider region. 

A deep flint wall along the north elevation of the extension provides protection and privacy to the living space within. In contrast, the glazed south elevation opens up to views over waterways. A structural framework of precast concrete profiles supports the roof and, in conjunction with the cantilevering roof overhang, provides both weathering protection and passive solar shading to the façade.

Internally, the exposed curved oak beams define the open-plan living area. An oak-clad kitchen with integrated sliding doors can be closed off from the rest of the space.

Eric Martin and Nikolai Delvendahl, partners, Delvendahl Martin Architects

KH House by Delvendahl Martin Architects

Project data 

Start on site January 2018
Completion January 2020
Gross internal floor area 135m²
Construction cost Undisclosed
Architect Delvendahl Martin Architects
Client Private
Structural engineer TZG Partnership
M&E consultant P3R Engineers
Quantity surveyor Romulus Construction
Project manager Tom Woolf
CDM co-ordinator BWA
Approved building inspector AIS
Main contractor Romulus Construction
CAD software used Vectorworks
Predicted design life 25+ years
Embodied/whole-life carbon 55 kgCO2/m² (incl. existing house)
Flint work subcontractor Mark Kennedy
Kitchen joiner Spa Bespoke Joinery
Copper roof subcontractor Eco Roofing

KH House by Delvendahl Martin Architects2

Architect’s choices

The precast concrete, flint and copper were selected following a thorough process of testing samples and 1:1 scale mock-ups.

In order to create a natural appearance, it was important that the flints were differently sized and randomly arranged across the wall, without any visible coursing.

In keeping with the overall desire to show the materials in their natural state, the oak beams and ceiling boards were left without applied finishes. The oak beams were rough-sawn and kiln-dried for several months to minimise deflections after installation.

The Vitrocsa window system was selected mainly for its minimal aluminium profiles and the large glazing areas it could support.

Stephanie Thum-Bonanno, project architect, Delvendahl Martin Architects

KH House by Delvendahl Martin Architects4


The primary materials of flint, precast concrete, oak and copper were selected for their tactility and robustness. 

There was a desire to simplify the construction build-up as far as possible (no plasterboard was used in the project) and to express the primary structure through the exposed oak roof beams and precast concrete framework.

Locally sourced materials and labour were used wherever possible. The use of flint along the north elevation of the extension references the walls of the existing farmhouse and was constructed by a local contractor specialising in this traditional construction method. The exposed oak beams and ceiling boards, as well as the external decking boards, are all sustainably sourced. 

Special attention was given to the detailing of the copper roof, which tapers at both ends in order to minimise the profile of the fascia. Projecting copper spouts direct rainwater away from the building. Over time, these materials will develop a natural patina that will help ground the project within the landscape of this Area of Outstanding Natural Beauty.

The careful selection and detailing of materials allows the extension to be contemporary while also sympathetic to the heritage and character of the listed farmhouse.

Stephanie Thum-Bonanno, project architect, Delvendahl Martin Architects

KH House by Delvendahl Martin Architects3

KH House by Delvendahl Martin Architects3


Selected products

KH House 6646

KH House 6652

KH House 6889

Locally sourced
Random split flints and lime-based mortar
North elevation

Tilt and turn windows
AWS 65 BS, powder-coated aluminium frames, RAL 7021, satin finish
North elevation

Absolute black granite, flamed finish
Kitchen worktop; fireplace surround

Untreated copper, TECU Classic

Engineered oak floorboards
Waxed Floors
Double-fumed oak white engineered boards, planed and oiled, 20 x 245mm

Glazing system with sliding doors
TH+32 system, PPC aluminium frames, RAL 7021, satin finish
South, east and west elevations

Oak beams
Supplied by Carpenter Oak & Woodland
Rough-sawn, kiln-dried, sandblasted French oak. No applied finishes

Precast concrete
Sterling Services
Fair-faced, heavy acid-etched precast concrete
Ground floor deck, below-ground floor structure, south elevation, window sills and lintels, gutters




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