Standard Spacing is 36 Inches
When installing batts or rolls of insulation below a floor or in a ceiling above, using insulation supports is a good idea. The standard suggestion is 36 inches apart. The wire supports should be fastened across the batt of insulation and tightly attached to the support beams.
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Steep Roofs Require More
For insulation under an extremely steep roof, 36-inch spacing still may allow sagging of roll insulation. In these cases, experts suggest 24 inches or even closer spacing of insulation supports.
For a standard installation, such as in a crawl space, using supports every 36 inches is fine. Use more supports for steep roofs.