The air barrier must be continuous and well sealed. But if the air barrier is too tight, how will fresh air get into the house?

First, most older houses are so loosely built that, even after extensive air-leakage control work, enough air will still come in to provide ventilation. Second, the air barrier is just the first step in the control of airflow.

The other essential steps include providing air for ventilation and air for combustion in a controlled manner. These steps may be necessary in houses where extensive retrofit work has already been done.

Read Chapter 9, "Operating your house," for essential information about ensuring proper ventilation and adequate combustion air for your home.