This article illustrates the concept and techniques of the Segal Method of construction. The Segal Method is a construction system employing timber frame lightweight construction used in conjunction with the self-build approach in housing. The first housing development using this method was built in 1977 in Lewisham, London. The scheme comprises eleven single-storey and three double-storey houses (Figure 1). It was followed by Lewisham II, where 13 double-storey units were built (Figure 2).
In 1968, Walter Segal, an architect working in London, needed a temporary residence built in his garden at Highgate while his house was being renovated. To minimise his expenditure on this temporary accommodation, he designed a home constructed of materials based on their uncut market sizes. The result was a four-bedroom timber frame house with infill panels, built in ten weeks at the cost of £800. Segal later applied for permanent planning approval, and the house still stands today.
The simplicity and clarity of the construction have led people to approach Segal to construct similar properties for them. Due to the practicality and simplicity of Segal’s construction method, one of his clients decided to do it himself. Segal saw the potential of developing self-build houses through this construction system. Eventually, the so-called Segal Method was refined and developed for self-build housing development.
The method aims to achieve optimum performance with minimum resources, and the method’s underlying theme is simplifying the whole building process from conception to completion. The idea of simplification is imposed in four areas:
1. Reduction of the number of trades on site
Working with a timber frame with an infill panel system eliminates “wet trades” on site, allowing the whole operation to be dominated by one trade only – carpentry. Other trades, such as roofers, electricians, and plumbers, can only be involved when needed.
2. A rational selection of building materials
The practicality and suitability of timber to the overall concept made it the best choice. Timber can be purchased easily in a large selection of standard sizes. It is relatively lightweight and can be used directly without further processing; hence easier to work with.
3. Simplification of the nature of site operation
Segal emphasised simplicity in all stages of construction because this would increase the buildability of the house by the inexperienced owners and save time and cost. Segal designed all the joints and detailing with the aim of keeping it simple. Double handling of materials on site is inefficient; hence, eliminated by erecting the frame and roof of the house to act as sheltered storage. Materials are ordered in the order of their stages of erection.
The house is raised on stilts, reducing the cost considerably because elaborate foundation work is not required. Paving slabs and concrete are sufficient to provide the necessary foundations. At the same time, stilt construction allows a house to be built on an uneven site. Furthermore, it can do away with a damp-proof membrane for the ground floor, as the raised construction prevents contact with soil and is well-ventilated. The lifted underside of the floor acts as servicing platform with a flexible service distribution configuration, allowing greater freedom in planning. The undercroft provides storage space and allows the accommodation of wind bracings, eliminating them in the wall.
4. Simplification of administrative procedures
Documentations are in A4 sheets made up of drawings (often freehand with minimum annotation), calculations, lists of elements, standard details and installation instructions for the whole building. Segal, acting not only as the architect but also responsible for administration works, achieved further savings in overhead costs. All these savings must be viewed not as a profit maximisation exercise on the part of the architect but rather as a step to minimise the cost to achieve good value for money on the client’s part.
Confirming the project’s available or intended financial resources from the client is necessary to avoid failure or professional incompetence.
Using gridded paper and models, Segal developed the basic plan layout to suit the client’s needs. He worked within the modular grid set from the width of the infill panels (600mm or 450mm) and the structural thickness (50mm). A wall thickness of 100mm or 150mm, either with foam plastic insulation or double layering of studs with horizontal counter battens, is commonly used to achieve a higher level of thermal insulation and avoid the formation of cold bridges through walling. The walls are non-load bearing, allowing space planning and openings flexibility. The vertical dimension is controlled by the height of the panels. The ceiling panels are fixed between structural frames without cutting, or if cut, without waste.
Upon confirmation of the layout, all required drawings are drawn freehand. These drawings are used in conjunction with structural framing, schedule of materials and other documentation.
The architect works out the structural layout based on the agreed basic layout. Columns are spaced six modules apart, allowing up to 3.85m span in either direction. For larger spans, composite beams or trusses can be employed.
Calculating each structural member is essential to ensure its adequacy in strength to support the load. These calculations are then submitted for building regulations approval.
Once the structures have been calculated, the detailed drawings of the frames, which include the foundation layout, roof plans, sections and detail of joints, are to be prepared.
Next, the detailed schedule of materials is arranged in the order of the erection stages. Apart from being the specification list, it also acts as a bill of quantities for the building. This leads to accurate costing, which is obtainable at a very early stage in construction. The final preparation in this process is to complete the description of how the building will be constructed – akin to an on-site working manual.
Holes are excavated, filled with concrete and capped with paving slabs to provide point foundations. The post stands on a piece of lead to prevent it from being affected by moisture rising through the end grains. The topsoil beneath the house is removed and replaced with gravel bordered by perimeter slabs.
b. Structural frame
Cross frames with rigid joints (using galvanised steel bolts) are assembled flat on the ground, then raised and braced into position to form the overall structure. Temporary props are used to achieve accurate positioning of frames.
A flat roof is chosen as it is easy to construct, economical and flexible to fit over any plan. To avoid leakages, the most common failure of traditional flat roofing, Segal laid out a waterproof membrane like a tablecloth instead of fixing it. This allows the membrane to shrink or expand without restraint and is free from stress caused by structural movement. Roof outlets are placed in the overhanging area of the roof, so the joint is fail-safe. The membrane is weighted down by shingles.
The floors use tongue and groove softwood boarding joists, with insulation between joists and panels. The panels are removable to allow access for services.
e. External walls
The completed floor provides the working platform to construct the walls. Originally, Segal designed walls made from non-structural infill panels clamped into the structural frame using bolts. This type of construction has a few deficiencies. Rigid insulation materials are expensive, can be environmentally unsound, and the construction can be draughty. The latest method of construction is to include the use of studs between clamping battens.
Upon completion of the external walls, windows are installed based on the materials available in the market. The preference for a prefabricated system is because modular coordination, tolerance, dependence on a single source of supply and delivery delays are minimal.
Internal partitions are made by clamping panels into frames with timber battens. A panel comprises a structural core, normally with a 50mm woodwool slab with painted plasterboard on both sides. It is held in place by a sole plate at the bottom and structural joists at the top.
These are painted plasterboards, and each panel is 600mm wide, laid between the joists on battens. Cover strips are used to mask the joints. Insulation and services are placed within the void of the structural depth.
i. Stairs and other features
Treads are supported either on hangars, posts or cantilevered beams. The basic structure can produce seats, a porch, a trellis, a verandah and a pergola.
The voids in the floors, roof and walls provide flexible space for service runs. They are accessible by unscrewing a batten or lifting out a panel.
The technical simplicity of the Segal Method could transfer the control of building construction from commercial developers into the hands of prospective owners/occupiers. This alternative approach to housing construction differs from the fabricated system in two ways. Firstly, it utilises basic raw materials in their uncut market sizes. The involvement of advanced intermediate manufacturing is not required due to the simplicity of the construction method. Secondly, the method allows labour with limited skills to construct the house. On the other hand, the fabricated system requires the skills of a trained specialist, which increases the construction cost. These two significant factors allow affordable quality housing in self-build schemes.
A good understanding of regional dynamics should be attained through research and study if the method is to be applied in different contexts. For example, material suitability and availability may differ from one country to another. The climatic requirements might also be an essential parameter in the development of the system.
Another important aspect is the potential of establishing self-help groups or organisations and consequently dealing with issues such as administration, management, funding, and on-site services, to name a few. Eventually, the system may have socio-economic implications that lead to an alternative approach to mass housing development. However, the method’s practicality might depend heavily on the country’s current economic and administrative frameworks.
Suggested readings :
Mc. Kean, John; Learning from Segal, Birkhauser Verlag, Basel Germany. (1989)
Borer P & C Haris; Out Of The Woods, Walter Segal Self Build Trust, London. (1994)
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