This paper reports the changes in the overall airtightness values of six tall Canadian office buildings. These buildings, which are 10 to 25 stories high, were built between 1964 and 1974 and were previously tested shortly after their construction. The results indicate that as a result of various retrofit measures applied, except for one building, the building envelopes are more airtight now than 20 years ago. The improvement in the overall airtightness value at 50 Pa ranges from 0 to 43% of its original value. Details are discussed in the paper.