Cavendish Avenue, Cambridge, Cambridgeshire

Introduction

Cavendish Avenue is a tree-lined suburban enclave rich in architectural character and domestic diversity. The houses are large yet individual, creating an interestingly disjointed street frontage. The new house - a contemporary ‘villa’ - replaces a 1930s detached house which was a crude amalgamation of modernist and rural cottage aesthetics, uncomfortably small and with a series of unfriendly spaces. The new house is designed to be of exemplary quality in design, scale and construction, reinforcing the existing overall architectural quality of the street. The house was very contentious at planning; however the council planning department are now known to use it as an example of how contemporary design can work in existing historic neighbourhoods. Since occupation, energy use has been monitored and the energy use meets stringent German Passivhaus standards for energy efficiency.

 

Building description

The scale of the house takes its form from the existing street, composed predominantly of large-scale three-storey dwellings set back from the street frontage. The house layout is a direct response to passive solar design and to the advantages of the north-south orientation of the site.

The north-facing façade, facing the street, is clad with a rainscreen of semi-reflective fritted glass. The glass partially reflects the sky above and is divided into small panels which add a delicacy to the façade and avoid a corporate feel. Openings to this street-facing façade are limited to three carefully placed windows which maintain the connection of the house to the street but protect the privacy of its occupants.

The small extension at the front of the house – dubbed ‘The Retreat’ by the client as it is remote from the TV – is clad with cedar shingles. It has a single large window, designed to act as a traditional ‘bay window’, a room to sit and watch passers-by in the street; it also gives personality and scale to the abstraction of the façade behind.

The predominant areas of glazing are on the south façade, at the rear of the house, which looks out over the garden. At first floor level the bedrooms have full-height windows. At ground floor level, the dining and living rooms have full-height sliding glass doors which open out to a paved terrace. Solar shading to the glazing on this façade is provided in the form of external fabric sunshades hung from an exposed timber frame, a series of structural glulam columns and beams bolted at junctions with steel flitch plates, which defines the terrace and which is itself an extension of the internal glulam structure of the house. The external fabric sunshades are adjustable and removable.

 

Use of timber and sustainability

Experience based on the design of three previous houses led Mole Architects to establish several basic principles for low energy use and sustainability:

  • Use of timber as primary structure

  • Highly insulated structure - 94mm thick solid cross-laminated timber and 230mm foamed glass insulation

  • Thermal mass and a weather-tight envelope

  • Restriction of overall sizes of windows, with openings predominantly on south façades

  • External solar sunshades to prevent overheating

  • Heat recovery ventilation for supply air

  • Cross ventilation and stack effect for purging heat.

     

Timber construction

The house is constructed of solid cross-laminated timber panels, making both the embodied energy of the building and the speed of construction very favourable. The architect, together with the structural engineer, the Cambridge office of Ramboll, compared the costs of a solid cross-laminated timber structure from KLH with a prefabricated timber stud structure. Although the KLH system was slightly higher in price, the advantages were clear, as the architect explains. ‘We have tried, over the years, to make a timber-framed building more robust by placing plywood on the inner face, behind the plasterboard. But a solid cross-laminated timber wall is inherently robust. It has fewer joints, so controlling infiltration losses is far easier. The loading capacity of the floor can be easily increased to allow a screed to be laid on the upper floors, increasing thermal capacity. It has also provided some beautiful rooms, with exposed timber ceilings and walls; in this house they have been coated with a translucent white Osma stain.’ The timber structure is a combination of cross-laminated panels and a glulam frame; on the south façade the glulam frame extends to the outside, creating a support frame for the external fabric sunshades.

 

External insulation and cladding

The choice of foamed glass (Foamglas) as an insulation material for external walls was made as the material is completely rigid, is unaffected by moisture and incorporates a high percentage of recycled glass. It is laid with staggered joints and sealed with a bitumen-based adhesive. On the south façade the insulation is overclad with cement fibre rainscreen panels, and on the north façade extension, with cedar shingles, both with a drained rear cavity.

The overall value of the wall/roof construction is calculated at 0.13W/m2K.Windows and doors are timber/aluminium composite construction with glazing to the highest specification available.

 

Other aspects of the sustainability strategy

Ground conditions made a ground slab possible, so that sub-floor ventilation and the associated difficult detailing, was not an issue. The slab was cast with kickers, on which the timber structure sits. The solid slab supports a screed floor with a black basalt stone finish; this acts as a solar heat sink. It also supports an internal dense concrete block ‘tower’ which rises through two floors adjacent to the staircase void and will further stabilise the internal temperature.

A ground source heat pump has been installed; it supplies hot water to a dual coil cylinder and to the underfloor heating within the screed on all floors. The fabric sunshades to the south rear elevation are designed as ‘sails’ to be hoisted up the ‘masts’ of the external exposed timber frame, and pulled in and out as required. They are taken down in winter. Stack effect ventilation is achieved by rooflights set at the top of the stairwell, shaded by external blinds. The house achieves the AECB Passivhaus benchmark for overall energy use.

Completion Date:

2008

Year Published:

May 2011

Building Type:

Private house

Location:

Cavendish Avenue, Cambridge

Architect:

Mole Architects

Structural Engineer:

Ramboll

Timber Structure Supplier:

KLH

Main Contractor:

Cambridge Building Company

Joinery:

Lawrence Smith Joinery

Timber Element(s):

Structure, cladding, staircase, external frame to terrace

Timber Specie(s):

Larch, cedar, oak, walnut

Awards:

RIBA Spirit of Ingenuity Award 2010: Sustainability: Winner Daily Telegraph British Homes Awards 2010: Winner Grand Designs Award: Best New Build: Finalist David Urwin Award: 2010 Winner Civic Trust Awards 2009: Shortlisted

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