Focus House, North London

Introduction

Focus House is something of an anomaly in its traditional Victorian London terrace setting, its zinc envelope contrasting markedly with the beige Victorian brickwork of its environs. The client had acquired the original Victorian house and an adjacent wedge shaped plot of land. He commissioned bere architects to design a low-cost, low energy, low-maintenance dwelling on the wedge shaped plot for his family, financed by the sale of the adjoining property. The new house was designed to be a radical departure from the inflexible and high maintenance Victorian dwelling that the family had previously occupied.

 

Building description

Following the wedge shape of its plot, at the pavement the house is only 2.8m wide and is set back to respect its Victorian neighbour. From this it widens to 7m at the rear – allowing room for a large light-filled living space and dining area furnished with an oak floor and rosewood fittings. Large timber sliding windows span the rear of the building, looking out over the garden and allowing light to flood in. Sufficient space was allowed at the rear to include a paved garden and a second low-level structure to be used as a study and recreation area. The narrow front of the house contains the utility areas and the stairs, which lead to a first floor study jutting out over the front entrance, 2 bedrooms and a bathroom, arranged in a linear sequence with a corridor connecting all rooms. A second flight of stairs connects the first floor to a second bathroom and master bedroom furnished with elegant oak cabinetry and a window which gives commanding views of the surrounding neighbourhood. The top rooms can be closed off from the children’s bedrooms below for privacy.

The whole space, 120 m² in total, is spatially innovative and yields a healthy living environment and a very low carbon footprint.

 

Materials and method of construction

The walls, floors and roof slabs consist of solid cross-laminated timber panels made of spruce from sustainable sources local to the manufacturer in Austria. The panels can span large distances and, as they are delivered in pre-cut sizes, they can be erected in a very short space of time. A concrete upstand was constructed to 150mm above ground level to receive the wall panels, which were generally one storey high and came with pre-cut window apertures and fixing points resin-bolted into the concrete. The thickness of the panels varies depending on loading, upper walls and floor panels being thinner than those at ground level. The first floor was bracketed to the wall panels, followed by the roof panels, and the whole structure was erected in only three days.

The building was completed from start on site to full fit out in only six months. Foamed glass (Foamglas) insulation was applied in pre-shaped blocks over the timber and bedded in bitumen. This created a thick insulation and impermeable vapour barrier. The Foamglas is clad with a zinc skin, (fixed to the insulation without cold bridging), providing a tough, durable exterior which further insulates the structure from the outside (This is a novel construction method which requires careful technical appraisal). High quality triple-glazed timber windows constitute a large percentage of the structure’s facades, particularly at the rear of the building. 

 

Structural engineer's account

The design of Focus House presented a number of structural problems. The constrained site required creative use of space, characterised by the cantilever section at the front of the house, which contained a study on a half landing level. Initial designs examined both steel and reinforced concrete (RC) options for the building structure with RC being the preferred choice to accommodate the large openings and cantilever spans. At the time bi-axial laminated timber was a relatively unknown product in the UK, but as a result of the high cost of the RC frame and a meeting with KLH UK, a timber solution was pursued.

The high strength to weight ratio of timber, together with the fact that the solid bi-axial laminated timber panels could behave as either walls or beams when orientated vertically, meant that the front cantilever section became easier to design efficiently. The side walls of the building could be engineered to behave as cantilever beams and the lighter weight structure meant they were easier to design. The rest of the building was designed as vertical loadbearing walls and horizontally spanning panels with cross walls where required.

The connections between panels are made with a number of screws, allowing the whole building to be brought to the UK on the back of a lorry and erected in a few days, much quicker than an equivalent steel or concrete building. The screws are large diameter and very long to accommodate the thickness of the material and are able to resist very large forces compared to traditional timber fixings. Construction tolerances on the material are considerably tighter than traditional in-situ forms of construction due to the off-site fabrication. This had the unexpected benefit of making window and cladding installation much quicker as there are fewer pieces required to take up the difference in tolerance. Other benefits of the timber structure included a lighter structure requiring smaller foundations and the lack of site waste during construction compared to a concrete scheme.

 

Sustainability

Focus House is designed on sustainable, ecological principles based on the German Passivhaus, the world’s leading standard in energy efficient design. Healthy air and water quality were ensured by the rigorous selection of non-toxic materials, automatic air ventilation and whole-house water filtration for drinking and bathing. CO2emissions are minimised with solar thermal water heating, low energy heat recovery ventilation, airtight construction, solid-core wood construction and excellent insulation.

By using a timber superstructure, the building has negligible levels of embodied energy, in contrast to an equivalent structure constructed from concrete and steel. Those embodied levels that exist are offset by the carbon dioxide contained within the timber during its lifetime.

The house is expected to generate 50-60% of its annual hot water requirements by means of the solar thermal installation. High quality timber windows combined with an efficient heat recovery ventilation system will reduce ventilation heat losses to a minimum. An average of over 200mm of Foamglas insulation on top of 200mm of solid wood will provide good winter insulation and the thermal capacity of Foamglas ensures particularly good summer protection from the heat of the sun. The client has already seen a significant decrease in energy costs over the past year.

Year Published:

March 2009

Building Type:

Private house

Location:

London

Architect:

bere architects

Structural Engineer:

Techniker

Quantity Surveyor:

Andrew Turner Company

Main Contractor:

Vision Build

Solid Timber Structure Sub-Contractor:

KLH UK

Timber Elements:

Solid timber panel floors and walls, windows

Timber Species:

Spruce

Awards:

RIBA London Awards Winner 2007 Grand Designs Awards Eco House of the Year 2007 British Homes Awards Small House of the Year 2007

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