NRCan Foundations Practice Exam

Infiltration is air entering a building through openings in the building envelope due to pressure differences. Any place where outside air can slip in—doors, windows, or access points like an attic hatch—can serve as a path for infiltration. Doors and windows are common entry points because they’re large openings that can have imperfect seals, especially under wind or pressure changes. An attic hatch is another practical entry point, since attic spaces are connected to the living space and may be poorly sealed or vented. Since all three can allow outside air to intrude, the best answer is all of the above.