Thermal performance and thermal resistance of fibre cement roof tiles: Experimental study

Abstract

A better understanding of the thermal performance of construction systems may help engineers and architects to select the most suitable materials for the solutions that meet their objectives. In warm-climate countries like Brazil, the thermal performance of roofs is of particular importance. Thus, this study presents an evaluation of the thermal performance of roofs built in reduced scale on an experimental test rig, in Florianópolis, capital of the state of Santa Catarina, southern Brazil. Four roofs were evaluated, all with fibre cement tiles and a polyvinyl chloride (PCV) ceiling: the first was used as a reference, the second had the tiles painted white, the third had a radiant barrier installed and the fourth had conventional thermal insulation based on expanded polystyrene (EPS). All roofs were instrumented with temperature and heat flow sensors and data was collected over a period of eight months. The results show that all of the test roofs had a lower thermal gain than the reference roof, with reductions of 55% for the roof with white tiles, 67% with a radiant barrier and 70% with conventional thermal insulation. The thermal resistance for downward heat flow of the roof with conventional thermal insulation was 1.29m2K/W and that of the roof with the radiant barrier was 1.20 m2K/W, with a difference between the two of only 7%. When comparing the thermal resistance obtained experimentally with values obtained with the international standard ISO 6946 and with the Brazilian standard NBR 15220-2 it was found that the radiant barrier roof presented the greatest differences, of 41% and 30%, respectively. This demonstrates that it is important to review the calculation procedure, especially when a radiant barrier is used for thermal insulation.