An insulating cover provides a easily removed thermal barrier over a hatchway used for access to an attic or other unheated area located above a heated living space. A cap, besides providing thermal insulation, provides an insulated dome or pocket space above the hatch, this space being used to manipulate a hatch cover or folding stairway. The seating surface of the insulating cap interlocks with a deck member on the attic floor sufficiently to hold it in place while allowing seepage of air during closing of the hatch cover or folding stairway. It is well known that such closing of a folding stairway of common design can cause an air movement or air rain into the stairwell opening. Only materials with high thermal "R" value are used.