Construction techniques can also influence the performance and effectiveness of space pressurization controls. Loose construction makes it difficult to establish an effective differential pressure in the space and large offsets are necessary to compensate. When large offsets are used, pulling large amounts of secondary air in from adjoining spaces, temperature and humidity control problems may result. Plugging all the holes and bypasses in the laboratory envelope during the renovation or construction process may be required to eliminate this problem. Duct leakage may also effect the accuracy and performance of ÆV systems. Air leaking out of or into the duct system between the flow measurement device and the laboratory envelope can result in significant error. In constant pressure systems this error may be relatively constant, but if the system static pressure floats then the error.