Between Floors Insulation: The Complete Australian Guide

For a new build or renovation where the floor cavity is accessible, installing insulation between floor joists is a relatively straightforward process. The insulation batts are cut to size and fitted snugly between each joist, with no gaps left that could compromise performance. For a suspended floor or timber floor system, care should be taken to ensure the batts are held securely in place so they do not sag over time. In a concrete slab construction, mid-floor insulation options are more complex, and professional advice is essential. The floor structure in these cases may require specific insulation products designed to work with concrete rather than timber joists. Building regulations require that insulation is installed to a minimum standard. Homeowners and builders are encouraged to meet or exceed these minimums, as the energy savings and comfort improvements from a well-insulated mid-floor are well worth the additional investment. Follow these steps for the best result:

Step 1: Measure Joist Spacing — Check the spacing between floor joists before ordering. Australian timber framing typically sits at 450mm or 600mm centres. Ordering the wrong width means gaps that hurt both acoustic and thermal performance.

Step 2: Seal All Penetrations — Fill any holes for cables, pipes, or ducting with acoustic sealant first. Unsealed gaps are the number one reason mid-floor insulation underperforms.

Step 3: Cut and Fit Batts Snugly — Cut batts to fit firmly between joists with no gaps and no compression. Compressed insulation loses R-value; gaps let noise and heat through.

Step 4: Insert from Below — With the ceiling cavity exposed, insert batts between floor joists systematically. Do not skip bays — even one uncovered section significantly reduces overall performance.

Step 5: Plasterboard Last — Once insulation is fully installed, fix the plasterboard ceiling. After this point the cavity is permanently sealed, so inspect thoroughly before closing up.

Step 6: Consider Resilient Channels — For superior impact noise reduction, resilient channels between the insulation and plasterboard decouple the ceiling from the floor structure above, reducing footstep vibrations between levels.