EcoHouse Research

Nathan Fieldsend (MEng, 2012)

 

With urbanisation continuing to occur at a considerable rate in many developing countries the United Nations Human Settlements Program estimates that by 2030 over half the world’s population will live in informal settlements or ‘slums’. Much of this growth is anticipated around urban centres of small to medium size rather than existing conurbations which can sprawl almost unchecked in some countries. The Program’s most recent report (2011) highlights the additional impacts which climate change may have on the stability, both economic and social, and quality of life for the inhabitants of these settlements.

 

Many organisations now exist, both governmental and non-governmental, which try to improve the living conditions in these types of settlements. Programs range from social inclusion activities, improving facilities or infrastructure (installing latrines or water supplies for example) right up to full scale rebuilding of homes or relocating families to new housing. This project examines the activities of a large non-governmental organisation in South America which provides heavily subsidised housing to vulnerable communities. Environmental sustainability of their operations has never previously been considered.

 

This project sets out not just to examine the activities of the organisation but also provide suggestions to improve the sustainability of their work. Whilst the context in which they work and the wider impact of their programs through service learning are of great importance, this project focusses primarily on the design implemented and the issues which arise from this. Significant problems currently exist with the design of the floor and foundations (excessive deflections of the floor under day to day use and differential settlements of the piled foundations) of the structure which have implications for safety, long term durability and adaptability.

 

An in-depth technical analysis of these components of the design was completed in order to ascertain where improvements would be most effective. European design codes were found to be a useful starting point for the analysis of the floor structure but were modified to give a more applicable code to the situation being designed for and avoid ‘over-engineering’ an inherently basic structure.

 

For the analysis of the foundations, recent research into the degradation of the stiffness of clay near to its ultimate strength was employed along with a more crude estimation of the behaviour of the soil to back calculate a set of parameters for the soil to be designed for. These values were then used to design an experiment to test the more basic estimation of the foundation behaviour against physical tests and to trial methods of improving the performance of the design. Poor correlation between the model tests and the approximate behaviour suggested was found but the experiments provided enough data and confirmation of the feasibility of a method to allow a full scale design to be developed.

 

Using fins or batons on the shaft of the pile was found to dramatically reduce the deflection of the pile in the conditions tested. Further work is required to understand fully the effects, if any, of different parameters such as the aspect ratio of the fins and their position on the shaft, on the behaviour of the pile. Moreover full scale testing of the designs will be required to ratify them. The soil conditions used in the laboratory can be changed to better match those where the designs will be implemented.

 

Two alternative designs were explored for the floor and foundations offering significant benefits in terms of performance. All were based upon the design currently implemented since buildability was a critical design parameter with strict limits imposed by the ngo. The financial cost of each suggestion was calculated and the environmental sustainability evaluated using figures for embodied carbon dioxide.

 

Due to the way in which the ngo has minimised the amount of material used in its current design in order to make it as cheap as possible, it was found that any alteration to the design which improved structural performance also increased the cost and environmental impact. Though this was a somewhat disappointing finding for a project which set out to make the activities of the ngo more environmentally sustainable, the figures alone did not encompass the longer term benefits of the alterations and the importance to the occupants of an improvement being made. The proposals would also increase the durability of the house which could offset the rises in cost and environmental impact.

 

Consideration was then given to the lifetime of the design. Three figures were of interest — the expected life of the current design, the actual life of the current design and the expected life of the improvements. The expected lifetimes of the alterations were longer than those of the current designs, and when the costs were normalised by lifetime the proposals represented an overall saving financially and environmentally. This finding highlights, as has been widely acknowledged by many agencies with much experience in the field of environmental sustainability, the need for proper lifetime analyses when considering impact of a project.