Light-weight, thermoplastic polymer-coated woven fabrics are in wide use today as roof covering membranes consisting of a plurality of strips which are electrically heat-welded in the factory to form unitary membranes which fit the contour of what may be termed "minimum pitched" roofs. Frequently, such membranes are installed over old roofing, and provide a roof covering which is reliably sealed, has excellent dimensional stability even with severe humidity and temperature changes, and does not become stiff, inflexible, or cracked when subjected to weathering, ultra violet rays, abrasions, and micro-organism attack.
Particularly on industrial roofs, provision must be made for the protrusion of large air-conditioning units, or make-up air units, which project from the roof surface. It is necessary that the membrane fabricated to fit the roof be provided with a vertically walled enclosure around the opening which is cut in the membrane so that the projecting unit may extend therefrom. The vertical walls which surround the air conditioning unit must then be sealed to the membrane and sealed to the air conditioning, or other unit, to absolutely prevent the entrance of any moisture, and provide an over-all, water-tight membrane which covers the roof.
The problem of enclosing vent pipe members which project from a roof structure has been solved recently for vent pipe enclosures, with the invention of the enclosure described in the present assignee's U.S. Pat. No. 4,652,321. However, it would be impractical to seek to form an enclosure, in the manner indicated in that patent, to surround and seal a housing as large as the casing of an air conditioning unit.