Redhill Barn, Devon

Introduction

Redhill Barn was once a large roofless ruin, standing in a Devon field without access, water or electricity. Within its stone walls the architectural practice TYPE has created a new home which is now the hub of an ecological smallholding. The character of the original building has been restored in a legible and original way. As Tom Powell, director of TYPE, explains: ‘Our strategy was to create a new home within the reconstructed barn rather than converting the barn into a house. We wanted to be very clear about what was old and new, retaining the weathered beauty of the monumental stone shell and wild agricultural setting.’ Key to this was the use of timber for new elements in the building; its lightness, variety of colour and its ability to be carefully crafted stand in contrast to the massive stone walls, articulating old from new.

Built in 1810, the barn had been laid out in the traditional way, its north wall built into the hillside to give access to the upper threshing floor and its south wall lined with a series of stone arches leading to the cow byre on the ground floor. This original massive stone envelope has been retained without making any new openings in the walls, the glazing set back within these openings to maximise natural light. A new Douglas fir roof structure supports a gutterless hipped roof covered with milled aluminium sheeting, ‘ghosting’ the original roof form in a light, reflective material.

The more cellular spaces – two bedrooms, a bathroom and kitchen – are on the ground floor, each room taking advantage of light from the south-facing arched doorways, while a staircase and utility rooms line the north wall. The upper floor is a generous light filled space for sitting, dining and relaxing, the main social space of the house. The gable ends of this space are partitioned with ‘floating boxes’ of timber, screening a study bedroom and a shower room.

The design approach to the barn reflected the client and architect’s commitment to sustainability, low-energy construction and its interface with the natural world. TYPE managed the project as a self-build, managing subcontractors and trades without a main contractor. The barn is now the centre of a secluded 25-acre site which is being regenerated and re-wilded by the client. It has a new access track and is equipped with an air-source heat pump, with permission granted for ground-mounted photovoltaics.

The use of timber

In contrast to the original massive stone walls, the new elements created within the walls are of timber, distinguishing old from new. The original timber first floor and roof had been completely lost and have been reinstated with Douglas fir structures designed to evoke the rhythm and simplicity of traditional barn structures. The new first floor structure of exposed joists and boards rests on internal stone columns. The roof structure above is a highly efficient truss which spans the building lengthways, positioned higher than a conventional truss to emphasise the height, form and scale of the first floor living space. To maintain this open volume, reminiscent of the original barn space, the two gable ends are screened with ‘floating’ sycamore-clad boxes 2.7 metres in height, so that the roof structure soars above them in an open and uninterrupted rhythm.

On the ground floor, the individual rooms – kitchen, bathroom and two bedrooms – are partitioned with vertical sycamore boards, with dark stained plywood for storage elements and partition doors. The external stone walls and columns are exposed and pointed with lime mortar. The ground floor rooms are lit by the south-facing arched openings that were originally made for cattle. They are fitted with glazed oak doors set back within the wall, operated with central pivots to accommodate the arch.

The organisation of the whole building is expressed through the different timber species, carefully chosen to suit their application. The Douglas fir structure is light and stiff, the sycamore ‘boxes’ are pale to reflect light, the oak for the doors and windows is durable, and the dark stained plywood for storage elements and partition doors is hardwearing and economic.

The roof structure

Colin Souch, consultant structural engineer to PCA Consulting Engineers, describes the design of the roof structure:

‘The concept for the roof truss arose out of discussions with Tom Powell of TYPE; the building was a derelict barn with no original floor or roof so, rather than reconstructing the original scissor truss, king post or queen post truss arrangement, we had the opportunity to design something slightly different.

PCA suggested a central girder truss based on a Pratt truss or Howe truss configuration which would be capable of spanning the full 18.5 metre length of the barn. As the roof finish was lightweight corrugated aluminium roof sheeting and as the overall roof construction build-up was not too onerous, the loadings would be manageable. The Pratt truss configuration was adopted as this would allow steel rods to be used as diagonal members, as opposed to the Howe truss where diagonal members are in compression. The use of steel rods also made the structure lighter in terms of its overall visual impact.

TYPE and PCA collaborated to enable a number of intricate design parameters to be accommodated in the truss design, with the architect suggesting a design aesthetic to achieve and PCA providing justification by analysis. One of these design parameters was to restrict the overall depth of the truss. Originally, it was proposed to minimise this to 1200mm overall to limit the impact of the truss within the vaulted ceiling, but lateral torsional buckling on a narrow long span truss made this difficult to achieve. The compromise was to limit the depth to 1.35 metres between the top and bottom cord axis.

The truss was designed with 67mm shear plates for all connections but the architect did not favour the use of timber shear plates or timber splice plates as this would make the truss appear bulky when viewed from below. The timber splice plates were replaced with steel plates and the central splice packer between the cords was replaced with a fabricated box section which also doubled to provide the connection for the diagonal tension rods. The most demanding design parameter to accommodate was the innovative splayed ends which had to accommodate the roof hips at the gable ends of the barn. This involved additional discrete splice plates.

Lateral torsion buckling was addressed by incorporating raised collars at 2.4 metre centres with the collars threaded through the compression struts of the truss. The overall stiffness of the roof was enhanced by sheathing the common rafters with fair-faced plywood.

The design solution developed between TYPE Studios and PCA was a good example of a ‘blank canvas’ approach with no preconceived ideas or restrictions. PCA had the experience to suggest distinct options and then adapt them to respond to innovative ideas and enhancements from the architect.’

Sustainability

FSC-certified and UK-grown timbers were used where available and other low embodied energy materials were used where possible. The external walls and first floor are insulated with sheep's wool, wood wool board and finished with lime plaster. The aluminium roof covering was chosen for its extreme longevity and recyclability, but crucially its light weight allowed the timber dimensions in the roof structure to be reduced to sustainable sizes.

Awards

Wood Awards 2020 – Highly Commended
RIBA South West Award 2021
RIBA South West Award for Conservation 2021
RIBA National Award 2021
RIBA Manser Medal 2021 – Shortlisted

Prepared by the publishing team with contributor Susan Dawson.

Completion date:

January 2020

Building type:

House

Location:

Devon

Architect, main contractor and project manager:

TYPE

Structural engineer:

PCA Consulting Engineers

Roof structure:

Carpenter Oak

Door and window joinery:

Bond Joinery Ltd

Timber supplier:

Beach Bros Ltd, Vastern Timber Ltd

Timber elements:

Roof and floor structure, partitions, doors and windows

Timber species:

FSC-certified Douglas fir, European oak, sycamore

Register to download the full case study with images and architectural drawings

Register

Suggested Reading

State of Trade Survey 2021 Q3navigation-arrow

The construction products manufacturing sector expanded for a fifth consecutive quarter in 2021 Q3, according to the latest Construction Products Association’s State of Trade Survey. This is despite escalating cost pressures and ongoing issues on the supply side that have been further exacerbated by a shortage of HGV drivers and...

26/11/2021

Construction Industry Forecasts Autumn 2021navigation-arrow

The Construction Products Association (CPA) has revised construction output growth up for 2021 from 13.7% to 14.3% since its previous Forecasts, but also revised down growth for 2022 from 6.3% to 4.8% in 2022. With more buoyant demand so far in 2021, supply chain constraints are expected to hinder growth...

26/10/2021

Design steps to stair safetynavigation-arrow

Too often design flair can compromise the safety of stairs presenting a risk of injury. Kevin Underwood looks at the four design characteristics that can make all the difference to stair safety, without compromising the aesthetic appeal.

 

Article from Timber 2021 Industry Yearbook

 

08/10/2021