Where attic spaces are created, Building Code requires minimum clearance to allow for airflow. In roof truss systems there is often less room at the eaves creating an area where insulation may be compressed. The minimum clearance is maintained at the eaves by installing baffles.

Baffles should to be installed prior to installing a vapour retarder and insulating the attic. Baffles serve two purposes, one is to maintain the required clearance for airflow between insulation and the under side of the roof deck, and the second one is to prevent air from flowing through the insulation product. Baffles increase air circulation within an attic space, therefore, not installing baffles prior to insulating can have a negative impact on the attic space.