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.
save energy

How To Save Energy & Electricity How to save energy around the home We lift the lid on where you can save the most energy in your home, no matter who you are or where you live. These simple changes will help to reduce energy costs and keep your home comfortable all year.

Material for insulating your ceiling 01:31

Heating & Cooling How to insulate a ceiling Keep your home warmer in winter and cooler in summer by insulating your ceilings. We’ll show you all you need to know about installing ceiling insulation.

Woman filling small gaps with insulation 01:18

Heating & Cooling How to insulate walls Installing insulation in your walls is a great way to increase energy efficiency and reduce noise. Learn how easy it is to do yourself.

Person holding an utility knife 03:24

Heating & Cooling How to insulate your home for extreme weather Find out how easy it is to keep your home warm in summer and cool in winter with insulation.

Pet doors 02:54

Heating & Cooling How to create an airtight home To have an airtight home, you’ll need to prevent airflow leaving your home. We’ll show you some places which may leak air and what you’ll need to do to reduce it.

Man installing glass wool insulation batts underfloor into joists 02:55

Heating & Cooling How to install underfloor insulation batts Insulating your home can save you money and energy. Find out how easy it is to fit glass wool insulation batts under your floor.

Man installing pleated foil insulation 05:48

Heating & Cooling How to install underfloor foil insulation Insulating your home is a great way to save money on heating and cooling costs. Learn how easy it is to install foil insulation in your subfloor.

Trim Special Shapes 03:58

Heating & Cooling How to install polystyrene insulation Save money on your energy bills by insulating your home. See how simple it is to do the job yourself.

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.

Top of the content