1 INTRODUCTION The reduction of greenhouse gases emissions, namely carbon dioxide (CO 2 ), and security have been identified by the European Commission as priority areas for action in order to comply with the Kyoto Protocol. And about 50% of the energy related to CO 2 emissions derive from energy use in buildings. The studies carried out in the nineties concluded that if any action was taken in 2020, Europe would import about 80% of the energy consumed and the energy use in buildings represents 40% of the total energy consumption in Europe, furthermore, implementing a set of economi- cally sustainable efficient measures, the potential of energy savings is more than 30%. To overcome this situation, in 2000, the European Commission identified the need to intro- duce specific measures in the building sector, namely with the Energy Performance Building Directive (EPBD) - 2002/91/EC - was published on 16 December 2002. This Directive propos- es the adoption of common methodologies for calculating energy consumption, quality re- quirements for new and existing buildings, periodic inspection of boilers and central systems air conditioning, as well as the buildings energy certification. Portugal must evaluate, according to the EPBD, the national requirements for energy perfor- mance of new buildings until 2011, which can be an excellent opportunity to draw up a national strategy tightening the minimum energy performance requirements. Reviews of national build- ing regulations should always be seen as an effective instrument for achieving highly energy ef- ficient buildings. The present study aims at analyzing the changes that should be introduced in the Portuguese Regulation, “RCCTE – Regulamento das Características de Comportamento Térmica dos Edifícios” for different scenarios in order to achieve very low energy demands in buildings. Portuguese Thermal Building Legislation and Strategies for the Future H. J. P. Gonçalves, M. J. N. Oliveira Panão & S.M.L. Camelo LNEG, Lisboa, Portugal ABSTRACT: Portugal must evaluate, according to the Energy Performance Building Directive, the national requirements for energy performance of new buildings until 2011, which can be an opportunity to devise a national strategy that tightens the minimum energy performance re- quirements. The present study intends to analyze the changes that should be introduced in the Portuguese Regulation to achieve highly energy efficient buildings. The objective consists on evaluating the relevant improvement of thermal envelope performance such as walls, roofs and floors thermal insulation (maximum U-values), air tightness (ventilation strategies) and win- dows (minimum shading requirements), heating and cooling systems, as well as wider use of in- tegrated renewable energy. The study considers apartments with different shape factors located in different climatic zones. The optimizing methodology makes use of a genetic algorithm for the estimation of primary heating and cooling energy indexes through a simplified calculation methodology established by Portuguese Regulation. Chapter 2: Policies to Low Cost Sustainable Construction 83