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How to install underfloor insulation batts

A person wearing protective gear placing an insulation batt between floor joists

Overview

Insulating your floor makes your home more comfortable and reduces your heating and cooling costs. We show you how to install the insulation batts yourself. You will learn how to put the batts in between the floor joists and trim them to size. We also show you how to install support strapping under the batts to stop them from sagging.

Steps

1Install strapping to support the glass wool floor insulation

Staple the strapping across the gap under your floor joists. Pull the strapping tight across the gap before stapling it in place. The manufacturer's instructions recommend installing at least three straps under each batt, but it is easier to simply lay a line of strapping every 200mm across the whole floor.
Floor joists with lengths of strapping underneath at regular intervals

2Install the glass wool insulation in the floor

Open the packets of batts one at a time and let the contents expand before you install them. Fluff each batt up and install it between the joists in your subfloor. To get the best results, keep the batts snugly together. If you have any small gaps left, trim the batt to size with you scissors.
A person wearing protective gear placing an insulation batt between floor joists
Health & Safety

Asbestos, lead-based paints and copper chromium arsenic (CCA) treated timber are health hazards you need to look out for when renovating older homes. These substances can easily be disturbed when renovating and exposure to them can cause a range of life-threatening diseases and conditions including cancer. For information on the dangers of asbestos, lead-based paint and CCA treated timber and tips for dealing with these materials contact your local council's Environmental Health Officer or visit our Health & Safety page.

When following our advice in our D.I.Y. videos, make sure you use all equipment, including PPE, safely by following the manufacturer’s instructions. Check that the equipment is suitable for the task and that PPE fits properly. If you are unsure, hire an expert to do the job or talk to a Bunnings Team Member.