As part of a programme to develop measurement methods for determining the ventilation rates of large buildings, we performed two series of tests in a single-celled laboratory with a volume of 600m3. The first series utilised constant concentration, constant emission and rate of decay tracer gas techniques to determine the characteristics of the infiltration pattern in varying winds and external temperatures. We used both discrete and continuous injection and sampling methods. Pressurisation techniques were employed to determine the overall leakage of the building and the spatial distribution of the leaks with flow visualisation methods. The building was then draught proofed with commonly available materials and techniques before further pressurisation tests and thorough ventilation measurements were undertaken. The experiment thus provided detailed comparisons of ventilation measurement methods and detailed performance characteristics of the building envelope in two states of leakiness, The interaction between the changed leakage characteristics and the measurement methods is discussed together with a critical evaluation of the measurement methods themselves.