Please refer to my previous blog post for some more detailed information on airtightness and SIGA products. Have a look at this article which discusses the importance of airtightness from a Passive House point of view. The Energy Saving Trust in the UK have produced nice guidelines on improving airtightness in dwellings that is worth a look and of course our own Department of the Environment, Local Community and Government has produced a document on air infiltration and thermal bridging as a supplement to the Building Regulations. Gavin O'Shea of GreenBuild has also produced an excellent document on blower door testing for passive houses. See below the video shown in class on how to carry out a blower door test.