Modular inflatable cover for buildings, comprising separate coaxial conduits (30) secured together by tensionable link (50) and fluid-connected by coaxial inflatable tube (24). Tube (24) securely embraces sliders (32) that in turn closely but freely embrace conduits (30). Sliders (32) are urged by springs (34) to keep tube (24) taught. Elastic cinctures (26) on tube (24) and springs (34) tensionably cooperate against inflation means to provide reliable control of openings between adjacent modules in an assembly. Conduits (30) are securely torqued to ground anchors (40) by coupling (42). End covers (44) and sliders (32) are provided to compensate for and facilitate length shrinkage of tube (24), upon inflation. The present invention provides a variable cover with integral support that is uniquely capable of exploiting canyons and other ground depressions for an unprecedented scale of environment control. Applications include greenhouses, shutters, insulation and shelters.