The viability of manually producing and using concrete roof tiles for low cost housing in South Africa
Bathke, Robert Michael
The roof is the element of a structure that provides the occupants with the greater part of the shelter they have from the elements. The roof covering is also the most exposed part of the structure and as such it not only has to offer acceptable thermal, acoustic and weather performance in order to provide the occupants with a comfortable living environment but it also has to be durable if the structure is to be considered a success. When considering low cost houses the requirements of the roof covering are the same as those mentioned above, except that they have to be met in the most cost-effective way possible. At present the most frequently usee' roof covering for both formal and informal low cost housing in South Africa is galvanised steel sheeting. This choice in roof covering is a compromise, it provides a durable, easily installed and most importantly a cheap roof while providing the occupants with exceptionally harsh living conditions. A survey conducted on the roof coverings available at this time on the South African market reveals that when selecting a roof covering for a low cost dwelling a compromise will have to be made. This is said due to the fact that none of the roof coverings surveyed satisfied all the requirements for an ideal low cost roof. A South African company, Hydraform, has proposed introducing a system that allows individuals to manually produce low cost concrete roof tiles. This system, namely the Agri- Tile system, utilises technology similar to that used by a number of other commercial companies which have successfully produced large numbers of [ow cost concrete tiles used on roofs in other countries. Case studies of three of these companies revealed that these low cost roof tiles provide acceptable levels of performance while remaining relatlvety cheap. lnltlal research into the strength and strength-gain-over-time characteristics of the Agri- Tiles (as well as the effect on the strength of the tiles when they were produced using five different fine aggregates) revealed that while this system of tile production has potential it also has a number of problems. The potential shown by the low cost concrete tiles, the need for such a roof covering on the South African market and the general lack of information encountered on the topic of low cost concrete tiles indicated that there is a need for a thorough evaluation of this system of tile production and of the tiles themselves. After consulting the South African Bureau of Standards and the Agrement Board of South Africa an evaluation of the tile production system, the tiles themselves and the material used to produce the tiles was undertaken using the Agri-Tile as a case study. The evaluation revealed that only afte" significant modification was the Agri-Tile system capable of producing tiles which, when produced in the controlled environment of the laboratory, consistently met the strength requirements of the South African Bureau of Standards. In addition, the modifications made to the tile production system eliminated the need for prefabricated moulds, which is the most expensive item of equipment needed to produce the tiles. The quality of the tiles was still highly dependent on tile workmanship used to produce them and as such no guarantee of quality will be available if the tiles are manufactured in an uncontrolled environment. Systematically changing the grading profile of the sand used to produce the tiles revealed that the tiles may be produced from a wide range of sands with different grading profiles without compromising the strength of the tiles. It was therefore concluded that in principal the Agri- Tile approach using the proposed moulding system and a very wide range of sands could make a contribution to the supply of low cost roofing material. However, strict control over quality would be necessary and the author doubts whether this cou' j be achieved consistently over a wide range of bui!ding sites.
Dissertation awarded with distinotion on IS May I999 A dissertation submitted to the faculty of Architecture, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree Master of Science in Building Management. Johannesburg 1998