In this study a novel zinc oxide nano-particulate water repellent emulsion was applied to brick and mortar samples. The treatment used was an aqueous silane/siloxane hybrid emulsion designed to penetrate deep into a substrate. Possible water repellence and thermal insulation for household energy saving was investigated. Tests on brick and mortar assessed; porosity, treatment depth, surface energy, water contact angle, thermal conductivity and visual aesthetics. In addition, two model houses were built with one treated with the emulsion. A heating and monitoring regime was developed to quantitatively evaluate heating energy consumption in different conditions. It was found that the treatment imparted significant water repellence and enhanced thermal insulation to treated samples. The results from contact angle and surface energy measurements showed that the substrates became highly hydrophobic. Experimental results from the model houses showed approximately 5% heating energy reduction in dry conditions and approximately 20% in wet conditions. In addition, the internal humidity was reduced across various temperature scenarios. Negligible aesthetical alteration of substrates and ease of application additionally prove that significant contribution can be made by similar treatments in future nationwide retrofit projects. (c) 2012 Elsevier B.V. All rights reserved.