In Nigeria, there is an estimated deficit of 17 million housing units. Power supply is insufficient, and the electricity supply for about 60 million Nigerians relies on private generators, causing noise, pollution, and high expenditures for mainly imported fuel. Altogether, current challenges clearly demonstrate the need for effective energy efficiency policies targeting also the building sector. The Nigerian Energy Support Program began in 2013, among others, with the objective being to support the Nigerian Government in developing the Nigerian Building Energy Efficiency Code. This paper presents two preparatory activities carried out in order to come up with suggestions for a legal framework well suited for the situation on the ground: the Case Study Building Analysis carried out in collaboration with a Nigerian developer and the Nigerian Building Energy Efficiency Guideline, elaborated together with stakeholders. The results of preparatory activities pointed out that the code must put emphasis on climate adaptive design and must define requirements and procedures in a clear and simple way to allow for effective enforcement. Only then can energy-efficient mass housing be feasible in Nigeria. The paper concludes with a description of the Nigerian Building Energy Efficiency Code (BEEC), officially approved and launched by the Federal Minister of Power, Works and Housing on 29 August 2017.