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Wednesday30 July 2014

Tectonics: Timber

Span house comes out of woodwork

Adrian Friend’s 21st Century Span House design.
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Using a modular typology of timber and glass, Friend & Company has reinvented an Eric Lyons Span house in south-east London

What is remarkable about the 21st Century Span House, designed by Adrian Friend of Friend & Company, is the inventive use of timber and structural glass to re-fabricate and transform a 1950s Span house into a home for this century.

Adrian Friend’s 21st Century Span House design (pictured, top) is for the rebuild of this 1959 Span house at Corner Green in Blackheath.

Adrian Friend’s 21st Century Span House design (pictured, top) is for the rebuild of this 1959 Span house at Corner Green in Blackheath.

The refurbishment project at Corner Green in Blackheath, south-east London, which is now on site and set to be finished by the end of the year, uses timber as a soft and forgiving material, mediating between laminated sheets of annealed glass.

STRENGTH IN LAYERS: The stringers comprise two sheets of 15mm float glass with a 1.52mm-thick PVB interlayer.

STRENGTH IN LAYERS: The stringers comprise two sheets of 15mm float glass with a 1.52mm-thick PVB interlayer.

The heart of this home is a timber-and-glass assembly that forms the kitchen, staircase and library. Within the house, all of the horizontal surfaces are made of timber, while all of the vertical components are made of glass. These are topped off by a frameless glass roof light that is opened by a manual winch.

Corner Green is considered to be one of Eric Lyons’ most successful housing developments for Span, comprising 23 T7/8 type terraced houses. Completed in 1959, it included the one millionth private house built since the end of the second world war.

The Span houses have a sparse economy that Friend has retained and built upon for his radical and inventive new interior.

GLASS OF ITS OWN: The laminated annealed single-piece glass stringers of each stair flight were cut by water jet using low iron or “water white” glass to reduce the greenish hue.

GLASS OF ITS OWN: The laminated annealed single-piece glass stringers of each stair flight were cut by water jet using low iron or “water white” glass to reduce the greenish hue.

A 1:40 scale model of the house made from maple and acrylic was exhibited at the 2008 Royal Academy of Arts summer exhibition.

The inspiration for this architecture has its roots in its mathematician client’s desire for a modular interior. In the imagination of Friend this became an ordered stack of timber, making reference to the timber bench designed by Eric Lyons for the public green that serves this housing. The house has been reordered using a 300mm by 40mm Douglas fir timber plank supplied by Danish timber specialist Dinesen.

Friend describes the project as “stripped-down modernism in tune with the original aspirations of the Span houses, creating an economic design where the quality of the finished materials can be fully appreciated”.

SEAL OF APPROVAL: The Douglas fir wood throughout the house will be sealed with Osmo Polyx, a wax and vegetable oil-based treatment.

SEAL OF APPROVAL: The Douglas fir wood throughout the house will be sealed with Osmo Polyx, a wax and vegetable oil-based treatment.

The Span houses showed it was possible to bring good design to the mass market. Continuing this tradition, Friend intends to develop his system of components with Graham Dodd, director of Arup Materials Consulting, to offer it as a customisable mass-market product.

The 21st Century Span House demonstrates both rigour in its detailing and completeness of architectural intent. It is made from a kit of explicit parts, and the result is a calm, restrained interior that gives the impression that nothing could be added nor taken away.

A Reciprocal structure

The kitchen, stairs and library of the 21st Century Span House have been designed as a reciprocal structure with no fixings. The glass supports the timber, which in turn supports the glass in a stacked assembly.

The glass has been mainly detailed as vertical sheets with a consistent dimension.

The exceptions to this are the single-piece glass stringers of each stair flight. Here, the laminated annealed glass has been cut by water jet to receive the timber treads. These are fitted with a snap-fit detail, more often used on small-scale product design. As the assembly has no fixing, tolerances have been very carefully worked out.

This assembly not only characterises the new interior, all setting out is driven by it. Overall lateral stability is ensured by the brick party wall and brick piers of the house.

The glass stringers were cut by water jet in Germany by Oswald using a low iron or “water white” glass. It is the iron oxide in common sand that gives most float glass its greenish hue, which is more pronounced the thicker the glass. The stringers are formed of two sheets of 15mm float glass with a 1.52mm-thick PVB interlayer. A single sheet of 15mm annealed glass is recognised as a safety glass by building regulations. The newel posts are a triple layer sandwich of timber and glass.

In the library, the span of the timber shelves is converted to reasonable measure — 1,050mm — by laminated “glass books”, which sit in notches in the shelves. They also serve as bookends. Most books are still paper products and are typically much denser and thus heavier than softwood.

The relationship and detailing of the timber-to-glass junctions depends on the location — from flush radiused tongues trapped by the stringer and balustrade to square-ended treads that are friction fitted into the stringer.

Friend selected 300mm-wide planks as the basic component for this house, thus worktops and landings are formed by biscuit jointing and gluing on site. Each timber component can still be read in the grain of the planks even when they have been bonded together.

The Douglas fir components of the 21st Century Span House will be sealed simply by being oiled with Osmo Polyx, a wax and vegetable oil-based treatment.

The long story of Douglas fir

Timber that is kept dry within a building stores the carbon dioxide that was absorbed by the trees as they grew.

It continues to store it until the building or its components reach the end of their life through combustion or decay. Each cubic metre of timber stores about 825kg of carbon dioxide. Thus, timber acts as a specifiable form of carbon capture.

Much improvement and innovation within the timber industry in the last 20 years has been based on engineered timber, which involves laminating together small timber sections to form knot-free stable window sections or massive timber panel systems manufactured by KLH or Finnforest Merk.

However, the supplier of the timber cladding for the 21st Century Span House, Dinesen, specialises in large planks of solid timber. The family-run company first supplied 15m long by 450mm-wide planks of Douglas fir in 1965 for the restoration of the 400-year-old Sønderborg Castle in South Jutland, Denmark.

Dinesen carefully manages the sustainability of its Douglas fir forests because these form the core of its industry.

The planks are cut from 90- and 120-year-old trees, thus the timber in the 21st Century Span House came from trees most likely planted at the end of 19th century, when Dinesen was founded.

Owners Heidi and Thomas Dinesen explain that Douglas fir trees “originally come from the west coast of North America, where it grows from California in the south to British Columbia in the north. The Douglas fir was introduced to Europe in 1827 and named after David Douglas, a Scottish botanist”.

Timber grows more slowly in colder, Scandinavian climates and so the trees have closer growth rings and better durability. It is supplied to site with a moisture content of 8-10% to minimise the risk of warping.

Project team

Architect Friend & Company Architects, Structural engineer Timothy George, Materials engineer Arup Materials Consulting, Timber Dinesen, Glass Oswald

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