Computational Water, Energy, and Environmental Engineering, 2014, 3, 152-161 Published Online October 2014 in SciRes. http://www.scirp.org/journal/cweee http://dx.doi.org/10.4236/cweee.2014.34016 How to cite this paper: Makaka, G. (2014) Influence of Fly Ash on Brick Properties and the Impact of Fly Ash Brick Walls on the Indoor Thermal Comfort for Passive Solar Energy Efficient House. Computational Water, Energy, and Environmental En- gineering, 3, 152-161. http://dx.doi.org/10.4236/cweee.2014.34016 Influence of Fly Ash on Brick Properties and the Impact of Fly Ash Brick Walls on the Indoor Thermal Comfort for Passive Solar Energy Efficient House Golden Makaka University of Fort Hare, Alice, South Africa Email: gmakaka@ufh.ac.za Received 3 July 2014; revised 17 August 2014; accepted 7 September 2014 Copyright © 2014 by author and Scientific Research Publishing Inc. This work is licensed under the Creative Commons Attribution International License (CC BY). http://creativecommons.org/licenses/by/4.0/ Abstract In quest for quality and sustainable development, it is necessary to find alternative materials, methods of brick making and house design. Bricks made in open kilns using locally available ma- terials usually do not meet the requirements of the South African Bureau of Standards; hence it needs to add some ingredients such as fly ash to produce better quality bricks. This paper reports the effects of fly ash on properties of clay bricks that can improve the thermal performance of buildings. Bricks of different clay and fly ash mixing proportions were molded. A passive solar house was designed and constructed using fly ash bricks. Results indicate that thermal conductiv- ity and water absorption decrease with increase in fly ash. Compressive strength was found to in- creases with increase in amount of fly ash. A mixing proportion of 50% of fly ash to 50% clay by volume produced a brick with the highest compressive strength, lowest thermal conductivity and minimum water absorption. The bricks were observed to have uniform size as they experience minimal burning shrinkage. These properties were found to have a significant impact on the thermal performance of the house. The mean indoor temperature swing was found to be 11˚C. Keywords Fly Ash, Thermal Performance, Passive Solar 1. Introduction In spite of being cheap, the locally made bricks possess some grave disadvantages, i.e. high water absorption,