Air tightness results for 40 New Zealand timber frame houses of varying age and construction detail are given. The steady pressure method was used at 6-9 indoor-outdoor pressure differences in the range 10-150 Pa. The data is presented in four ways: 1. air changes per hour at 50 Pa, 2. the coefficient and exponent of a generalized leakage function, 3. the leakage rate per unit shell area at 50 Pa, and 4. the equivalent leakage area at 50 Pa. Houses in the 0-5 and 6-20 year age groups were not significantly different in terms of air tightness. The greater than 20 year age group were less tight. Air leakage around openable doors and windows made up 17% of the total envelope leakage in houses less than 5 years old and 23% in older houses. The air tightness test has only limited application in locating leakage openings for weatherstripping because of the number of leaks.