Project Overview

Insulating your floor with polystyrene panels is a cost-effective way to help reduce your heating and cooling bills. We show you how to trim the panels to size and install them between your floor joists. You will also see how to use brackets to support the panels in place.
Continue to Step-by-step instructions.
Time Required

Done in a Day

Done in a Day

You'll need to set aside a day to comfortably complete this project


Step by Step Instructions

1 Prepare your joists for installing the polystyrene insulation
2 Trim polystyrene insulation panels to size
3 Fit support brackets for the polystyrene insulation
4 Trim special shapes in the polystyrene insulation
  • Step 1. Prepare your joists for installing the polystyrene insulation

    Check to see if there is any plumbing or electrical cable installed on the sides of your joists. If you find electrical cable, cover it with wireguard waxed paper. If you find plumbing, cut a gap in your polystyrene panel that leaves 100mm of clearance to allow for future maintenance.
  • Step 2. Trim polystyrene insulation panels to size

    Polystyrene insulation panels come in different sizes to match the standard widths between floor joists. When you find a smaller width, trim the panels to fit the size required. Each panel has accordion edges, so you can easily trim them on either side with a standard trimming knife
  • Step 3. Fit support brackets for the polystyrene insulation

    Place a bracket once every 600mm on both sides of every joist, approximately 60mm below the top of the joist. This will hold the insulation panels in place just below the top of the joist. Nail the brackets in lightly. Then use a panel offcut to confirm your brackets are in the right position before nailing them in fully. Now put your panels in place.
  • Step 4. Trim special shapes in the polystyrene insulation

    Polystyrene insulation panels are easy to trim. For very thin gaps between joists, it is possible to trim the accordion edges on both sides. When the floor joists have an odd shape or overlap one another, you can simply cut a notch out where you need to.
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Please make sure you use all equipment appropriately and safely when following the advice in these D.I.Y. videos. You need to be familiar with how to use equipment safely and follow the instructions which came with the equipment. If you are unsure, you may feel it is safest to consult an expert, such as the manufacturer or an expert Bunnings team member.

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