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The hidden box: creating a bespoke prefabricated house

06 np house r hidden box
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Magnus Nilsson tells how his practice, Nilsson Pflugfelder, created the bespoke House R on an inaccessible backland site in Cambridge, using a German prefab system

This two-storey new build house with three bedrooms is built on a backland site in central Cambridge, surrounded by Victorian terraces and their back gardens. The plot is relatively small, with a usable area of only 520m2. A narrow driveway affords the only access to the site. 

Weighing environmental credentials, quality and speed of construction and cost certainty, it was decided from the outset that the house would be built and supplied by the UK branch of the German prefab house manufacturer Baufritz.

Baufritz homes are assembled from prefabricated timber wall and roof panels that are completely finished within a controlled environment at a production plant. The panels are transported to site by lorry and hoisted in place by crane. A weatherproof shell is typically erected within three days. Once the shell is standing, all construction work takes place within, which helps prevent potential damage through rain and moisture. In addition, disturbance to neighbours is kept to a minimum and site wastage is reduced.

Non-standard details and materials tend to be prohibitively expensive

Prefab construction seems to be in a state of transition at the moment. While CNC-milling and automated construction processes are available and indeed used, many prefab manufacturers nevertheless still tend, in various degrees, to favour rectangular footprints with pitched roofs, thus not yet fully realising the potential of such production methods. What is more, within many prefab systems there are built-in orthodoxies, which have to do with the specific history of the various prefab manufacturers. Non-orthogonal geometries, non-standard windows, non-standard details and non-standard materials, as well as set-backs, for example, tend to be penalised, making such items prohibitively expensive. In other words, the various systems tend to be biased towards certain preset solutions and configurations.

The tendency towards relatively simple orthogonal shapes is further enhanced by the fact that prefab construction often tends to be panel-based. A typical timber frame construction is structurally very flexible, because loads, more or less, are distributed throughout the entire frame. A panel-based system, on the other hand, acts structurally like a house of cards: lateral stability is an issue and overhangs are likewise difficult to achieve. The number of openings in the façades and the area of these openings are also limited in order to provide sufficient stability.

11 np house r hidden box

11 np house r hidden box

Source: Joakim Boren

Oriel window detail

Although we think form is important, we also feel that architecture’s obsession with form has run its course. After an era of exorbitant forms, the response was non-form, and currently we see many buildings that return to sombre tectonic façades, often carried out in brick. Architecture is an endless chain of actions and reactions but, unlike in the past, these new movements do not replace the preceding –ism, they all add up, coexisting in a Babylonian cacophony. Such a jumble of styles renders form and expression, to a certain extent, meaningless, as they become pure fashion, signifying nothing beyond their own appearance.

Given this contemporary polyvalent condition, we believe the future of architectural praxis lies not so much in the elaboration of new (or the recycling of old) forms and motifs, but rather in the idea of what architecture really is and how it is formulated at an operative meta-level. This argument is certainly not intended to be some form of fundamentalist position, a return to a singular truth, but rather an attempt to stay operative in a polyvalent condition where meaning has become elusive and interchangeable. Prefab construction, in this sense, provides a new productive platform that side-steps many orthodoxies inherent in architectural thinking and production.

We have, over the years, found it to be unrealistic to challenge the basic premises of the prefab system and have come to accept it as a given mode of praxis that could almost be said to be a form of non-design, an arrangement of ready-made solutions and off-the-shelf elements. Design is, in this view, a strategic application of add-ons where architecture is created through addition and assemblage. 

07 np house r hidden box

07 np house r hidden box

Source: Joakim Boren

View from west

In practical terms, when using prefab systems, we thus tend to pursue orthogonal geometries, concentrating on very basic architectural qualities such as proportion and the relation between open and solid surfaces. The appearance of finished prefabricated façade panels is generally of an exceptionally high quality, whereas the standard detailing between different materials tends to be less attractive and more costly. That means we often refrain from mixing materials, letting the timber cladding speak for itself through large, uninterrupted surfaces. If any further articulation of the otherwise potentially ‘naked’ volume is required, this is, as mentioned above, done by adding accessories such as projecting timber profiles, brise-soleil, pergolas, screens, canopies, balconies, or bay windows to the basic volume. To a certain extent one could say prefab houses designed in this way are more akin to a product, rather than architecture in the traditional sense.

The add-ons evolved organically in response to the requirements of the site

In the case of House R, the site required a compact, orthogonal footprint. Likewise, it was necessary to keep the height of the house as low as possible, which meant that a flat roof was the most favourable option, pragmatically resulting in an unadorned orthogonal box, ideal for prefab construction. 

The add-ons evolved organically in response to the requirements of the site. In order to, for example, ensure that there were no overlooking issues at this backland site, accessories such as visibility fins and an oriel window were added. The most complicated issue to resolve was the choice of cladding material. The context is predominantly clad with buff-coloured brick. Brick, however, is not part of the standard material palette offered by Baufritz. 

As the given construction system is biased towards lighter cladding materials, a standard off-the-shelf cladding product consisting of untreated 28mm solid horizontal timber was chosen. Through strong horizontal striations added to the cladding, and by leaving the timber untreated, it is intended, through eventual weathering and deposits of soot, that the lightweight timber cladding will acquire a materiality and weight more akin to a heavy brick façade. It was the intention, in other words, to make the timber appear brick-like, and thus contextual.

Pflugfelder drawings 1

Pflugfelder drawings 1

Project data

Start on site April 2016
House site assembly 27-30 April 2016
Completion August 2016
Gross internal floor area 249m2 
Form of contract Design and Build
Construction cost £610,900
Construction cost per m² £2,050
Architect Nilsson Pflugfelder
Client Private
Main contractor Baufritz UK
Planning consultant RPS Planning and Development
Landscape Sara Mark
Groundworks Gary Gabriel Associates
Project manager Dominik Boehm
Structural engineer Baufritz
M&E consultant Baufritz
Quantity surveyor Robert Lumme (Baufritz)
Approved building inspector MLM Building Control

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