the factory fabricated expansion joint cover is an assembly of three components as shown in fig1 wherein : a is a single - ply roofing membrane b is a bonding adhesive ; and c is a flexible foam . the unique part of this assembly is two - fold : the bonding b , between the foam c , and the roofing membrane a , is only at the center of the foam leaving portions of the foam un - bonded to the membrane ; and the un - bonded foam extending down into the joint opening is the primary force producing the bellows shape extending above the joint opening as shown in the attached drawings . fig2 shows a typical installation of this invention over a joint opening in a roof - to - roof application wherein : j is the roof deck with an insulation i is the roofing membrane or system n is a vapor barrier m is a compressible insulation l is the un - bonded foam portion of the expansion joint cover bellows extending down into the joint opening d is the bellows portion extending above the adjacent roofs referred to as the “ typical shape of a flexible bellows style expansion joint cover ”. k is a canted area adjacent to the joint opening to shed water away for the joint opening e is the flexible foam bonded to the underside of the single - ply roofing membrane g is the side flange where it is sealed to the roofing system ; ( the style and materials used to effect this seal vary depending on the roofing ; pvc , tpo , bur , and others ) h is the caulking or edge sealant to seal the edge of the flange to the roofing system . when the expansion joint cover is set in place , the un - bonded foam portions “ l ” are placed down into the expansion joint opening while the attached membrane flanges are spread out onto the adjacent roof decks . no metal or rigid nailing strips are needed when installing the expansion joint cover ; the un - bonded foam “ l ” extending into the joint opening , produces a compression seal against the vertical faces of the expansion joint opening helping seal the joint opening ; the un - bonded foam of the bellows extending into the opening holds the expansion joint cover in place and helps free the hands of the installer to make a permanent seavattachment to the roofing system on each side of the joint opening ; the tensioning provided by the un - bonded foam sections extending into the joint opening helps prevent the bellows from dropping inverted ; if the bellows drop inverted , it would form a trough that collects water and debris that can lead to failure of the joint system ; and reduces installation labor . fig3 shows a typical roof - to - wall installation of the expansion joint cover of the present invention . this design comprises a vapor barrier w , attached to the roof deck and the wall forming a support to hold the compressible insulation v . the flexible foam is bonded to the roofing membrane from one edge where it meets the wall p , to a point where the bellows meets the cant on the roof deck . the flange r , extends from this point out onto the roofing membrane where it is welded or sealed in place s . the un - bonded portion of the foam extends down into the joint opening u , forming a compression seal against the vertical surface of the roof deck . the flange on the wall side is sealed to the wall o , by welding the flange . this installation forms the typical flexible bellows shape for a roof - to - wall or curb - to - wall installation . the seals of the flanges to the wall and roof will be based on the roofing systems being used . fig4 shows a curb - to - curb application of the expansion joint cover of the present invention . in this design the un - bonded portion of the foam is installed as in a roof - to - roof installation . the roofing extends to the edge of the opening and the membrane flanges of this invention are welded or bonded to the vertical face of the curb . the flanges of this invention can be varied to allow the flange to extend out onto the roof deck on one or both sides . while there has been shown and described what is considered to be preferred embodiments of the invention , it will be understood that various modifications and changes in form or detail could be readily made without departing from the spirit of the invention . for example the membrane flanges shown could be modified by welding or bonding a ridged nailing strip for particular application needs or the flexible foam could be a round foam tube or rod . it is therefore intended that the invention not be limited to the exact forms described and illustrated , but should be construed to cover all modifications that may fall within the appended claims .