Wednesday, 19 March 2014

The wall

The wall has developed greatly, especially in the last 100 years.  This has been to enable improvements in building performance and living conditions, giving us better thermal resistance, air tightness and damp protection.  The development of the wall tells a lot about how the building industry works and how innovation works within it.  In particular, many of the materials used since tudor times (timber, brick, plaster), are used today and innovative developments seem to add layers of processes to the construction of the wall, with every development potentially adding work to the process.

The Tudor timber frame wall is relatively simple but does not perform well in relation to contemporary building standards.  Three site processes to construct included frame, infill panel and external plaster (if required).  Thermal resistance for a wattle and daub wall would typically be 2.2 w/m2k.  It would also be draughty with potential damp issues.

Timber frame wall, pre nineteenth century
1 Timber frame,  
2 External plaster,  
3 Infill panel in stone, brick or wattle and daub

The solid stone wall was similar with a thermal resistance of around 2.1 w/m2k depending upon quality of construction and overall thickness. With internal plaster, it requires two processes with potential drafts and damp still an issue. 

Stone wall, pre nineteenth century
1 Stone blocks,  
2 Mortar,
3 internal plaster

With the introduction of the mass produced brick, the Victorians could build and build. It was also one of the first modular building components which meant less cutting on site compared to stonework, an innovation allowing quicker construction. Typically thermal resistance is about 1.5 w/m2k with air tightness and damp still potential issues. 

Nineteenth century Victorian solid brick wall
1 Brickwork pattern (eg English bond),
2 Internal plaster

The introduction of the insulated cavity brick wall addressed thermal resistance with insulation, and damp with the ventilation cavity and membranes. Thermal resistance might be 0.5 to 0.2 w/m2k depending upon the age of the insulation and Building Regulations at the time of construction. The insulated cavity brick wall represents about 6 processes including damp membranes across the wall. Although the processes increased, these additional steps did not involve heavy building work. The reduction of heavy labour might be considered as an innovation in this development.  Air tightness remained a possible issue. 

Twentieth century insulated cavity brick wall
1 Outer layer of brickwork,  
2 Inner layer of blockwork,  
3 Insulation,  
4 Cavity with ties between masonry layers,  
5 Internal plaster finish

The modern timber frame wall went some way to address air tightness. Large panels in the inner wall construction reduced potential air gaps, with the membranes over the wall surface assisting. Approximately 8 processes with thermal resistance easily able to meet 0.2 w/m2k. 

Modern timber frame wall
1 External facing panel (eg brickwork restrained back to building frame),
2 Timber frame,
3 Insulation,
4 Weatherboard to cavity side of wall,
5 Breather membrane
6 Ties, restraints or supports between outer panel and wall as required,
7 Vapour barrier to inside face of insulation and frame,
8 Internal plasterboard finish

Structural Insulated Panels (SIPs) or engineered panels came as an innovation for introducing more bespoke prefabricated components to the building sequence. This has not necessarily lessened the number of processes to build a wall but does improve the performance of many areas (structural, thermal, air tightness and moisture resistance).  With the panel at the core of the wall system, all other layers need to be added. These panel often need specialised lifting plant and as before, the additional processes involve less heavy building labour. 

Wall with Structural Insulated Panel (SIP) or similar
1 SIP or engineered panel,
2 Breather membrane,
3 Supports to facing panel within cavity,
4 External facing panel, eg brick slips on backing board
5 Vapour barrier to inside face of panel
6 Spacing battens for internal cavity for balance of panel, and to allow location of services,
7 Internal plasterboard finish  

In this example innovation is hidden and the evolution of the wall as a series of layers might shed some light on the workings of the building industry, as traditionalist innovators

Where simpler aesthetics are appropriate and where buildings can work to larger regimented modular spacings (usually industrial units), composite panels offer a solution which can be achieved in 2 site processes (structure and panel). This alternative product is perhaps closer to the industrialised systems of other industrial sectors such as the aircraft industry.  The air cavity is eliminated because the wall panel is a single closed component there moisture levels trapped within the materials can be controlled.

Industrial panel
1 Metal faced insulated composite panel
2 Structural steelwork supports

(It's also worth making a note on the igloo. This simple structure uses only one material, needs no fixings and is completely recyclable and biodegradable. Naive as it might seem, when considering innovation in the building industry, should we keep these values in mind?)

The igloo
1 Blocks cut from ice
2 More ice used to bond blocks together

By comparison, where changes in the fuselage of aircraft take place, it generally involves a complete rethink of the materials, production systems, and assembly methods. Solutions have developed from timber frame and canvas, to aluminium frame and plywood, to aluminium semi-monocoque and stressed skin, to the the full composite monocoque.  The innovative developments are there to read on the product without being hidden.  

History of aircraft at the RAF Museum, North London

How much of this is to do with each aircraft producer being in charge of what their entire product, from design to production including material selection?  Economies of production, material resources and programme are critical, as are the performance criteria of the aircraft.  With one producer overseeing the whole process does this lead to more holistic innovations? Arguably the professional structures and lines of communication in these industries might be less fragmented than those in the building industry, demonstrating continued offensive innovation strategies.


The Boeing production line

Perhaps one day the shape of the british building industry will not look too dissimilar from this, with a single controlling business organisation taking charge of design, fabrication and production of buildings and whole building systems?  Then would we see more radical innovation within buildings as a product?

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