Joists 4x8 at 48" On-Center

There is rarely an excess of headroom in a crawl space. I seek methods where no headroom is lost, and nothing attached to joist under-sides will snag a passerby. Effort is needed to draw batts into contact with the floor, and away from interference with a person wanting to pass under.

Here is a versatile method, corresponding to that in a completed crawl space with joists 4x6 at 32" oc.

This method will work with fiberglass batts. More work is needed to cope with heavy cotton, UltraTouch batts. The work to create intimate contact with flooring, and along batt edges, is very important. With an average 6" gap best effort with twine, the situation is wasteful of a large investment. Drawn close, there is highly desirable mouse habitat, where nest constellations can devour batts, becoming foul.

A Neat R25 Installation, Done Before Increase of Required Insulation, To R30:

Johns Manville R25 kraft batts have consistent, rigid full thickness. There is minimum projection below floor joists. 17 gage steel electric fence wire is wound onto shingle nails about 2" above joist faces. Wires are loaded with lengths of wood lath to retain the insulation There is nothing to snag on in passage under joists and insulation. The second photo shows the installation process, rolling a batt over a wire, and then pressing it up against floor sheathing.