An insulation system for metal buildings, having a roof structure formed by roof panels supported on parallel, relatively narrowly-spaced purlins which are, in turn, supported on parallel, relatively widely-spaced main support beams, comprises a plurality of adjacently positioned strips of insulating material suspended below the roof structure so as to form a relatively flat and continuous surface. The strips of insulating material are supported on a system of insulation support tube strings suspended from and extending in parallel spaced relation to selected purlins. Each insulation support tube string runs the entire length of the building in spaced and transverse relationship to the main support beams.